Enhancing biogas production from co-digestion of organic wastes mixed with cattle manure using rumen fluid and Saccharomyces cerevisiae isolate MUTJ0F

Mulugeta Fentahun; Birhanu Kahsay

doi:10.12688/f1000research.161561.3

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Research Article

Revised

Enhancing biogas production from co-digestion of organic wastes mixed with cattle manure using rumen fluid and Saccharomyces cerevisiae isolate MUTJ0F

[version 3; peer review: 1 approved with reservations, 2 not approved]

Mulugeta Fentahun ¹, Birhanu Kahsay²

PUBLISHED 18 Apr 2026

Author details Author details

¹ College of Natural and Computational Sciences, Department of Biology, Debre Markos University, Debre Markos, Amhara, 269, Ethiopia
² Institute of Biotechnology, Mekelle University, Mek'ele, Tigray, Ethiopia

Mulugeta Fentahun
Roles: Conceptualization, Data Curation, Formal Analysis, Funding Acquisition, Investigation, Project Administration, Resources, Software, Supervision, Validation, Visualization, Writing – Original Draft Preparation, Writing – Review & Editing

Birhanu Kahsay
Roles: Conceptualization, Data Curation, Investigation, Methodology, Resources, Software, Validation, Writing – Review & Editing

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Abstract

Background

Biogas production from various types of biodegradable waste is a cost-effective, environmentally friendly, and sustainable alternative to fossil fuels, and provides a reliable method for handling food waste.

Methods

This study evaluated the effects of rumen fluid and S. cerevisiae isolate MUTJ0F as digestion activators on biogas production from the co-digestion of cattle manure, fruit and vegetable waste, and cafeteria leftover food. Under mesophilic conditions (38°C), 12 treatments with different rumen fluid (0–150 ml/100 g) and S. cerevisiae isolate MUTJ0F inoculum (5–10 ml/100 g) dosages were assessed. Biogas was produced from mixed waste using plastic digesters (0.6 L) after the 60-day retention period.

Result

Rumen fluid with S. cerevisiae isolate MUTJ0F increased biogas generation by more than four times compared to the uninoculated control. The combination of 100 ml rumen fluid and 10 ml S. cerevisiae isolate MUTJ0F per 100 g of mixed waste produced the highest volume of biogas (6900.3 ml). pH variations in digesters revealed normal acidogenesis followed by a gradual return to methanogenesis conditions, while combustibility tests showed the presence of biogas in the digester.

Conclusion

These results suggest that using rumen fluid and the S. cerevisiae isolate MUTJ0F as inoculants in a biogas digester can enhance the efficiency of biogas production.

Keywords

Anaerobic digestion, Biogas production, Inoculum, Rumen fluid

Corresponding author: Mulugeta Fentahun

Competing interests: No competing interests were disclosed.

Grant information: This research was supported by Debre Markos University.
The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Copyright: © 2026 Fentahun M and Kahsay B. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

How to cite: Fentahun M and Kahsay B. Enhancing biogas production from co-digestion of organic wastes mixed with cattle manure using rumen fluid and Saccharomyces cerevisiae isolate MUTJ0F [version 3; peer review: 1 approved with reservations, 2 not approved]. F1000Research 2026, 14:199 (https://doi.org/10.12688/f1000research.161561.3) First published: 13 Feb 2025, 14:199 (https://doi.org/10.12688/f1000research.161561.1) Latest published: 09 Jun 2026, 14:199 (https://doi.org/10.12688/f1000research.161561.4)

Revised Amendments from Version 2

The manuscript has been extensively revised based on the feedback provided by the reviewers. The abstract section of the manuscript has been revised to remove redundant methodology. The introduction of the manuscript has been revised to highlight the urgency and significance of the research hypothesis needs to be justified in terms of the economy and environment. The introduction section of the manuscript has been revised by merging the sentences to enhance the readability of the manuscript. The redundant data presented in the introduction part has been removed to avoid repetition. The materials and methods section of the manuscript has been extensively revised to update the knowledge by revising the experimental method based on the recent literature. The results and discussion section of the manuscript has been revised. Figure 1, Figure 2, and Figure 3 have been included in the manuscript text. The conclusions section of the manuscript has been revised to briefly mention the results of the research and the recommendations. The manuscript has been extensively edited for language usage.

See the authors' detailed response to the review by Dominic Yellezuome
See the authors' detailed response to the review by Jovine Kamuhabwa Emmanuel
See the authors' detailed response to the review by Josef Marousek

1. Introduction

The search for sustainable energy alternatives is increasing owing to growing concerns about the effects of fossil fuel consumption on the environment and the rapid depletion of the world’s petroleum reserves (Akinbami et al., 2001; Imri and Valeria, 2007). To address these challenges, long-term strategies for sustainable development place greater emphasis on switching to renewable energy sources that can lessen reliance on finite fossil fuels and mitigate environmental degradation (Farid, 2022). Among the available options, renewable energy technologies, especially biogas have become practical, economical, and environmentally sustainable for energy generation (Alemayehu, 2014; Arthur and Brew-Hammond, 2010). Anaerobic digestion of biomass or organic waste produces biogas, which is used for various household and commercial purposes, such as cooking, heating, lighting, electricity production, and vehicle fuel (Harris, 2008; Corral et al., 2008; Nasir et al., 2012).

Biogas production depends on the activity of various bacteria and microorganisms that break down organic matter in anaerobic digestion (Membere et al., 2012). An innovative solution to increase anaerobic waste digestion yields is co-digestion, which is an inexpensive and simple technology that enhances the anaerobic digestion rate by creating a better nutrient balance from the materials mixed to feed the digester, provides positive synergism for bacterial growth, and increases biogas production (Huang et al., 2016; Abbas et al., 2021).

Hydrolysis, acidogenesis, acetogenesis, and methanogenesis are the four interdependent microbial stages of anaerobic digestion, which are carried out by fermentative, acidogenic, and methanogenic microbial communities (Jia et al., 2020). Rumen fluid is a waste product from slaughterhouses that is regularly dumped into drainage systems (Zhang et al., 2016). Rumen is an anaerobic microbial habitat found in ruminant animals and harbors a diverse population of microbes, which includes fungi, bacteria, protozoa, and archaea (Sylvester et al., 2004; Yue and Yu, 2009). The rumen could be helpful as an activator in the anaerobic fermentation process that produces biogas. This fermentation process resembles the biogas digester process (Achmad et al., 2011). Saccharomyces cerevisiae is an anaerobic microorganism that can increase fiber degradation, stimulate cellulolytic bacterial and fungal growth, and increase the pH in digesters through organic acid production (Lynd et al., 2002; Achmad et al., 2011).

Debre Markos University is one of Ethiopia’s federal universities, and currently, there are more than 20,000 resident students on the main campus during the regular academic year and summer. For this reason, these students have their meals at the university. We have an enormous amount of organic waste and leftover food, which can be utilized as inputs for the generation of anaerobic biogas. The primary ingredients of the meals provided to students at Debre Markos University include bread, injera, spaghetti, rice, meat, and various stews and sauces. Rumen liquid is a slaughterhouse waste that is frequently disposed in drainage systems. This waste disposal system can create environmental problems and potential health hazards because rumen liquid contains millions of microorganisms. Similarly, most cafeteria leftover food was disposed around the back side of the male student dormitory, which creates a bad smell and a suitable environment for the growth of pathogenic bacteria. Different juice house wastes are also among the municipal wastes that are becoming a problem for management. Usually, this type of waste is disposed in dumping sites along with other types of domestic waste, which greatly pollutes the environment in Debre Markos town. Likewise, the dumping site has limited capacity owing to the scarcity of land. Therefore, there is a need to find other solutions to manage organic waste.

The major inputs required for biogas production in this study, such as rumen fluid, organic waste, and cattle manure, are locally available at minimal cost. Saccharomyces cerevisiae cultures can be propagated using inexpensive substrates. Therefore, the improved biogas production from organic waste mixed with cattle manure using rumen fluid and Saccharomyces cerevisiae isolate MUTJ0F can reduce household energy expenses, making the process economically feasible. Although there is information on biogas production from organic waste using rumen fluid inoculum (Aragaw et al., 2013; Tamirat et al., 2013; Tamrat, 2012; Yue and Yu, 2009; Zhang et al., 2016), but there is limited report on methods for increasing biogas generation, particularly those that use rumen fluid and S. cerevisiae (Achmad et al., 2011). This study aimed to determine the effect of rumen fluid and S. cerevisiae isolate MUTJ0F as digestion activators on the amount of biogas generated from co-digestion of food wastes mixed with cattle manure under anaerobic conditions, and to optimize the volume of rumen fluid and S. cerevisiae isolate MUTJ0F for biogas production. Therefore, the results may help universities, municipalities, and small businesses implement effective waste-to-energy management, encourage renewable energy, and reduce environmental pollution.

2. Methods

2.1 The study area

The research was carried out in the microbiology laboratory of the Department of Biology, Debre Markos University, East Gojjam, Ethiopia. The university is located in Debre Markos. Debre Markos is located at latitude and longitude of 10°20’N 37°43′E/10.330°N 37.717°E, elevation of 2,446 meters above sea level. It is 300 km away from Addis Ababa, the capital city of Ethiopia, and 265 km from Bahir Dar, the capital city of the Amhara region. In Debre Markos, there are 133,810 residents, comprising 67, 606 men and 66, 204 women (ESA, 2021). The average annual rainfall is 380 mm, while the lowest and maximum temperatures are 15°C and 22°C, respectively.

2.2 Yeast strain used in experiments

The strain Saccharomyces cerevisiae isolate MUTJ0F (OR209280.1) with accession number was used in this study. The Saccharomyces cerevisiae strain MUTJ0F (OR209280.1) was acquired from stock cultures from a previous isolated traditional fermented alcoholic beverage (Tej) in Ethiopia. The methods used for their isolation and identification have been described in our previous studies. Sequenced data was deposited in GenBank in the NCBI database, and accession numbers were obtained (Fentahun and Andualem, 2024).

2.3 Substrate collection and preparation

This study aimed to evaluate the effects of ruminant fluids and S. cerevisiae isolate MUTJ0F (OR209280.1) on biogas generation from various mixed organic wastes co-digested with cattle manure. Various wastes of fruits and vegetables were gathered from the town fruit houses, cafeteria leftover food from the Debre Markos University student cafeteria, fresh cattle manure (CM) from Monkorer Agroindustry Enterprise, and rumen fluids (RL) from a nearby slaughterhouse.

Unwanted, non-digestible materials were carefully separated from the substrate. Food scraps from leftovers were gathered daily for a week from the cafeteria of students found in the Main Campus of Debre Markos University. Indigestible waste, such as bones was carefully removed from the substrate of the gathered meal. A mixture of substrates, including peels of papaya, mango, banana, avocado, as well as bread, injera, and spaghetti was used in this study. To improve and maintain the anaerobic digestion process, the organic wastes were manually chopped to a size of 1–4 mm (Leta et al., 2015). The CM was spread to dry for two days in direct sunlight on a plastic tray, then it was shredded to an average particle size of 2 mm and kept in a refrigerator at 4°C (Tamirat et al., 2013). After measuring the total solids (TS) of the samples, the de-sized cattle manure and food waste were mixed separately with distilled water in a 1:5 ratio (w/v) to maintain the total solid in the digester between 8 and 15%, which is the optimum value for wet anaerobic digestion (Ituen et al., 2007).

2.4 Preparation of inoculums

Rumen fluid was filtered through a double-layer sterile cheesecloth to remove coarse feed particles and fibrous impurities. After filtering the rumen fluid, the filtrate was stored in a refrigerator until use. Then, different amounts of the filtrate were added to each digester to initiate the reaction. The S. cerevisiae isolate MUTJ0F inoculum was prepared in Yeast Extract Peptone Dextrose Broth (YEPD) (Sigma-Aldrich (Oxoid Limited, USA) medium containing (g/l): yeast extract 10, peptone 20, and dextrose 20. The medium was sterilized at 121°C for 15 min in an autoclave. A loop full of a chosen 48 h old culture was inoculated into a 250 ml flask with 100 ml of the medium, and it was then shaken at room temperature at 25°C on a rotary shaker (SHKA4450-1 CE) (121 rpm) for 72 h. Each digester received a specific inoculum.

2.5 Analysis of the physicochemical properties of the substrate

Total solids (TS), volatile solids (VS), fixed solids (FS), moisture content, organic carbon, and pH were measured in each sample of cattle manure, cafeteria leftover food, and fruit and vegetable waste using standard methods.

2.5.1 Total solids (TS)

According to APHA (1999), the oven-drying method was used to determine the total solids (TS) content of each sample. An evaporating dish (crucible) was first carefully cleaned, dried for an hour at 105°C in an oven, cooled in a desiccator, and precisely weighed. Using a standard analytical balance (LX200ABL), five grams of each sample of cattle manure, fruit, and vegetable waste was weighed independently and added to a crucible that had already been weighed. Subsequently, the crucibles containing the samples were placed in an oven (Contherm 260 M) set to 105°C for 24 h to dry. The crucibles were dried, cooled to room temperature in a desiccator, and weighed again.

Using the formula stated in APHA (1999), the percentage of the TS was determined as follows.

% TS = \frac{mDS}{mFS} \times 100

Where,

% TS = percentage of total solid

mDS = mass of dry sample

mFS = mass of fresh sample.

2.5.2 Volatile solids (VS)

The previously dried total solids were ignited in a muffle furnace (BiBBY, Stuart) at 550°C for 3 h to determine the volatile solids (VS) and fixed solids (FS). The crucibles were removed after ignition, allowed to cool in a desiccator, and then precisely weighed. The volatile solids were represented by the weight loss during combustion, and the fixed solids were represented by the remaining residue. Then volatile solid content in the sample was determined using the formula: APHA (1999).

% VS = \frac{mDS - m (ash)}{mDS} \times 100

Where, mDS = mass of dry samples whereas m(ash) = mass of ash

2.5.3 Organic carbon (C)

According to Jigar (2015), the organic carbon content of the sample was calculated from volatile solids data using an empirical equation stated below:

% carbon = \frac{% VS}{1.8}

2.5.4 Moisture content determination

The moisture content of each sample was calculated using the oven-drying method, which measures the percentage of water lost relative to the initial wet weight of the sample. After carefully weighing 10 grams of each sample, it was placed in oven (Contherm 260 M) at 105°C for 24 h set to 105°C for an entire day. The samples were weighed again after drying and cooling in a desiccator. Moisture content was then calculated using the formula (Elias et al., 2010):

% MC = \frac{W - D}{W} \times 100

where W is the sample’s initial weight (g), D is the sample’s weight during a 24 h drying period at 105°C, and M is the moisture content.

2.5.5 pH determination

The pH of each sample was determined using a digital pH meter (Hanna ECI pH meter, Hanna Scientific, USA) in accordance with standard procedures. The pH meter was calibrated using standard buffer solutions of pH 4.0 and 7.0 before measurement to ensure accuracy throughout the relevant pH range. After calibration, the electrode was rinsed with distilled water, inserted into the substrate samples, and the pH values were recorded.

2.6 Experimental set up

This study consisted of the anaerobic digestion of substrates in 12 treatments. The 12 treatment types used for anaerobic co-digestion were cattle manure, fruit and vegetable waste, and cafeteria leftover food in mixtures of 1:1 ratio. The first experimental variables was the dosage of rumen liquid i.e. (0 ml/100 g, 25 ml/100 g, 50 ml/100 g, 75 ml/100 g, 100 ml/100 g, and 150 ml/100 g), while the second variables was the dosage of S. cerevisiae isolate MUTJ0F i.e. (5 ml/100 g, and 10 ml/100 g) of the mixed organic waste. Three replicates were used for each treatment. All digesters were kept at 38°C in an oven set to mesophilic conditions. The water content of each digester was calculated according to the suggestion of (Ituen et al., 2007). Feed stock was mixed with distilled water to obtain approximately 8% of TS suspension. The following formula was then used to determine the amount of water to be added:

8 % = \frac{mFTS}{A + B}

where A is the mass of the freshly added sample, B is the amount of water and inoculums to be added in order to achieve an 8% TS suspension in the digester, and mFTS is the mass of the fixed total solid.

2.7 Construction of the anaerobic digesters for batch system

Anaerobic digesters (plastic bottles) were constructed for bench-scale experiments, in which biogas was produced from the degradation of substrates in a 0.6 L digester with a working volume of 450 mL. The three plastic bottles were set up such that the substrate was in the first bottle, the acidified brine solution was in the center, and the last bottle collected the brine solution expelled from the second container. All three containers were interconnected with a plastic tube with a diameter of 1 cm. The lids of all digesters were tightly sealed using superglue to control the entry of oxygen and loss of biogas.

An acidified brine solution was prepared by adding NaCl to water until a saturated solution was obtained. The brine solution was then acidified by adding two to three drops of sulfuric acid, and the solution was placed in the second chamber according to the method of (Elijah et al., 2009). The biogas was moved to the second chamber while it was being produced in the digester chamber. A pressure buildup served as the catalyst for the solution displacement because the biogas is insoluble in it. The amount of gas collected was equal to the amount of water that was pushed from the digester. By looking at the cylinder’s graduation, the displacement of water was measured. According to Budiyono et al. (2010), the “liquid displacement method” was used to measure the amount of biogas produced. Biogas volume was measured daily throughout the experimental period using the water displacement method.

2.8 Burning test

A burning test was performed to qualitatively determine whether the biogas contained methane. After the biogas was collected, a measurement cylinder containing the gas was carefully placed. A lit matchstick was brought close to the mouth of the cylinder while observations were made. If the gas started a fire and created a flame, it was a sign that the biogas contained flammable methane. However, if there was no flame, the gas was considered non-combustible, indicating that there was very little or no methane in the sample.

2.9 Data analysis

Version 23.0 of SPSS (IBM SPSSInc., Chicago, IL, SPSS (RRID:SCR_002865), https://www.ibm.com/support/pages/downloading-ibm-spss-statistics-23) was used to analyze the data. The mean and standard deviations of the triplicates analysis were calculated using analysis of variance (ANOVA).

3. Results and Discussion

3.1 Analysis of the physicochemical properties and composition of the different substrates

The physicochemical properties of the different substrates, such as their moisture content, pH, organic carbon, total solids, fixed solids and volatile solids are shown in Table 1. The pre-digestion of three substrates, including cattle manure, cafeteria leftover food, and vegetable and fruit waste, varied owing to the differences in the composition of the substrates. The pH of the different substrates ranged from 6.8 to 7.6, which is within the ideal range for anaerobic digestion. This near-neutral pH is useful to start microbial activity, which thrive in stable pH environments (Budiyono et al., 2010). The high moisture content of the mixed wastes ranged from 62.5 to 77.6%, which increases microbial accessibility and substrate solubilization for anaerobic digestion (Fernández et al., 2008). The physicochemical characteristics of the different substrates showed a low percentage of volatile solids relative to the total solids. The VS of cafeteria leftover food waste was greater (30.8%) than that of cattle manure and fruit and vegetable wastes, suggesting a comparatively higher energy content that is advantageous for biogas production.

Table 1. Physicochemical properties of different substrates (mean ± SD).

No	Component	Percent by weight (% w/w)	Total solid (TS)	Volatile solids (VS)	Fixed solids (FS)	Organic carbon (C)	Moisture content (MC)	pH	VS/TS (%)
1	Cafeteria leftover food	22.5 ± 0.15	39.4 ± 0.06	30.8 ± 0.12	69.2 ± 0.05	41.6 ± 0.23	62.5 ± 0.21	7.6 ± 0.21	78.3 ± 0.36
2	Vegetable and fruit waste	17.3 ± 0.1	31.5 ± 0.3	25.2 ± 0.06	74.8 ± 0.15	34.4 ± 0.15	66.3 ± 0.06	6.8 ± 0.06	80.2 ± 0.87
3	Cattle manure waste	47.8 ± 0.12	21.3 ± 0.15	19.4 ± 0.1	80.6 ± 0.12	25.3 ± 0.1	77.6 ± 0.12	6.8 ± 0.06	91.2 ± 1
	Total	100	-	-	-	-	-	-	-

The VS/TS ratios of the cafeteria leftovers food, vegetable and fruit wastes, and cattle manure were 78.3%, 80.2%, and 91.2%, respectively. These values indicate sufficient biodegradable volatile solids for effective anaerobic digestion, and the biodegradable organic matter was within the recommended 70–95% range for efficient biogas production (Kawai et al., 2014; Wu et al., 2021).

Among the substrates, cafeteria leftover food had the highest organic carbon content (41.6%), which is indicative of its rich protein, fat, and carbohydrate content. This makes it a high-energy feedstock with significant potential for biogas production (Panahi et al., 2022; Zeng et al., 2022). All of the substrates were considered acceptable for anaerobic digestion because all the different substrate wastes had the highest ratio of VS to TS in Table 1. Cattle dung is used to accelerate biogas production by promoting bacterial growth in the digester (Adeoye, 2024).

3.2 The effect of rumen liquid and S. cerevisiae isolate MUTJ0F on biogas production

The amount of biogas generated from digester using rumen fluids and S. cerevisiae isolate MUTJ0F as a fermentation activator is presented in (Table 2; Figure 1). The 12 methane production treatments varied significantly due to variations in inoculum dosage of rumen fluid and S. cerevisiae isolate MUTJ0F. The combination of mixed waste with rumen fluid and S. cerevisiae isolate MUTJ0F significantly improved anaerobic digestion at mesophilic temperature (38°C) compared to the control (without inoculum). This implies that the high anaerobic bacterial concentration in rumen fluid with S. cerevisiae isolate MUTJ0F efficiently breaks down organic substrates from mixed waste. These findings are consistent with those of other researchers (Achmad et al., 2011; Sakar et al., 2008; Yitayal, 2011; Forster-Carneiro et al., 2008; Abdullahi et al., 2011).

Table 2. The effect biogas production on 12 treatments used in anaerobic digestion of mixed wastes combinations with rumen fluid and S. cerevisiae isolate MUTJ0F doses (ml).

Treatments	Mixed Wastes (MW) 100 g	Rumen fluid	S. cerevisiae isolate MUTJ0F	Biogas (mean ± SD)
T1	MW₁	0 ml RF	5 ml	1600 ± 0.49 ml
T2	MW₂	0 ml RF	10 ml	1600 ± 0.62 ml
T3	MW₃	25 ml RF	5 ml	2100.7 ± 0.67 ml
T4	MW₄	25 ml RF	10 ml	2300.3 ± 0.17 ml
T5	MW₅	50 ml RF	5 ml	3400.4 ± 0.49 ml
T6	MW₆	50 ml RF	10 ml	3800.6 ± 0.56 ml
T7	MW₇	75 ml RF	5 ml	6000.4 ± 0.17 ml
T8	MW₈	75 ml RF	10 ml	6500.5 ± 0.25 ml
T9	MW₉	100 ml RF	5 ml	6800.4 ± 0.12 ml
T10	MW₁₀	100 ml RF	10 ml	6900.3 ± 0.26 ml
T11	MW₁₁	150 ml RF	5 ml	6300.57 ± 0.47 ml
T12	MW₁₂	150 ml RF	10 ml	6350.13 ± 0.06 ml
T control	MW₀	0 ml RF	0 ml	1500.2 ± 0.1 ml

Figure 1. Biogas production.

A. Mix of wastes which was subjected to digesters; B. Experimental setup (a. Digester; b. Gas collector; c. Water collector).

According to the results, the maximum amount of biogas (6900.3 ml) was produced by combining 100 ml of rumen fluids with 10 ml of S. cerevisiae isolate MUTJ0F/100 g mixed waste, followed by 100 ml of rumen fluids and 5 ml of S. cerevisiae isolate MUTJ0F/100 g mixed waste. These results demonstrate that co-inoculation with S. cerevisiae isolate MUTJ0F and rumen fluid significantly increases biogas productivity by enriching the microbial community involved in hydrolysis, acidogenesis, and methanogenesis. The digester with the lowest methane volume (1500.2 ml) was the control digester (without inoculum), which contained only mixed waste without yeast or rumen fluid. This demonstrates that external microbial stimulants significantly increase the efficiency of anaerobic digestion.

As the digester rumen content varies, the results also showed that the amount of biogas generated increases when the dose of S. cerevisiae isolate MUTJ0F is increased from 5 ml to 10 ml. The addition of the S. cerevisiae isolate MUTJ0F culture to the digester enhanced the number of ruminal bacteria and their activity while also improving the digestibility of dry matter, crude protein, and hemicelluloses (Wilson, 2011; Wandera et al., 2018).

3.3 pH variations in digestors during digestion

The pH value was checked every 10 days to examine the effect of change during digestion on bacterial activity (Figure 2). The result showed that the variation of pH values during 80 days of the digestion process in all treatments (T1–T12) and the control. At the beginning of the experiment (day 0), the pH values in all treatments ranged from about 7.2 to 7.6, indicating a neutral environment, which is suitable for the start of anaerobic digestion. The pH values gradually dropped throughout the first phase (days 0–30), with most treatments reaching their lowest levels between pH 4.2 and 5.8. This drop may be likely caused by the formation of organic acids and volatile fatty acids during the hydrolysis and acidogenesis stages of anaerobic digestion (Joyce et al., 2018; Li et al., 2018). On the other hand, after day 30, the values of pH gradually increased in all treatments. This increase may be due to ammonification processes in which the breakdown of proteins releases ammonia, which buffers the system and increases alkalinity (Zhang et al., 2014; Yaichurrozi et al., 2016). All treatments showed pH values ranged from 7.4 to 7.9 at the end of the experiment (day 80). This indicates that the digestion process was stable after the active biogas production period. Methanogenic bacteria the optimum pH values between 6.8 and 7.2 (Anunputtikul and Rodtong, 2004; Budiyono et al., 2010).

Figure 2. pH variation during the digestion process.

3.4 Combustibility of biogas

A lit matchstick was brought near the digester gas outlet to evaluate the biogas combustibility after the 60^th day of the digestion period in a 0.6 L digester. Flammable gas was observed at the digester gas outlet, confirming the presence of biogas in the digester (Figure 3).

Figure 3. Combustibility of biogas.

A. 0.6 L plastic bottle digesters; B. Combustibility of biogas test.

4. Conclusion

This study showed that the co-digestion of mixed organic waste with S. cerevisiae isolate MUTJ0F and rumen fluid is a feasible method for significantly improving biogas production in anaerobic environments. Among all treatments, a mixture of 100 ml rumen fluid and 10 ml S. cerevisiae isolate MUTJ0F/100 g of mixed waste produced the highest volume of biogas (6900.3 ml). pH variations in the digesters showed a typical anaerobic digestion pattern, with an initial decline due to active acidogenesis, followed by a gradual return to methanogenesis conditions. Using rumen fluid and S. cerevisiae as bioactivators provides a valuable, affordable, and effective way to increase the production of biogas from readily accessible organic wastes, such as fruit and vegetable waste, cattle manure, and cafeteria leftover food. The sludge (digestate) produced from biogas production can be used as organic fertilizer to enhance the fertility of the soil. Future research should focus on scaling up the experiment to a pilot scale to determine its commercial feasibility. Institutions such as universities, agro-industries, and municipalities that produce large amounts of leftover food and fruit-vegetable waste should implement co-digestion systems using these inoculants for better waste management, improvement of public health, reduction of environmental pollution, and production of renewable energy.

Author contribution statement

Conceptualization, M.F. and B.K; Methodology, B.K.; Data analysis, M.F.; Investigation, M.F. and B.K.; Resources, M.F. and B.K.; Writing – original draft, M.F.; Writing – review and editing, M.F. and B.K.; Visualization, M.F.; Funding acquisition, M.F. All authors have read and agreed to the published the manuscript.

Consent for publication

Not applicable.

Ethical approval

Not applicable.

Data availability statement

Underlying data

Figshare: The effect biogas production on 12 treatments used in anaerobic digestion of mixed wastes combinations with rumen fluid and S. cerevisiae isolate MUTJ0F doses (ml) of data analysis. https://doi.org/10.6084/m9.figshare.28284806 (Fentahun and Kashay, 2025).

This project contains the following underlying data:

- Raw data. Physico chemical properties of mixed wastes of data analysis.

Data are available under the terms of the Creative Commons Attribution 4.0 International license (CC-BY 4.0).

Acknowledgments

We want to express our gratitude to Debre Markos University for financial support.

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Version 4

VERSION 4 PUBLISHED 13 Feb 2025

Author details Author details

Birhanu Kahsay
Roles: Conceptualization, Data Curation, Investigation, Methodology, Resources, Software, Validation, Writing – Review & Editing

Competing interests

No competing interests were disclosed.

Grant information

This research was supported by Debre Markos University.
The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Article Versions (4)

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Published: 18 Apr 2026, 14:199

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Fentahun M and Kahsay B. Enhancing biogas production from co-digestion of organic wastes mixed with cattle manure using rumen fluid and Saccharomyces cerevisiae isolate MUTJ0F [version 3; peer review: 1 approved with reservations, 2 not approved]. F1000Research 2026, 14:199 (https://doi.org/10.12688/f1000research.161561.3)

NOTE: If applicable, it is important to ensure the information in square brackets after the title is included in all citations of this article.

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ApprovedThe paper is scientifically sound in its current form and only minor, if any, improvements are suggested

Approved with reservations A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.

Not approvedFundamental flaws in the paper seriously undermine the findings and conclusions

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Reviewer Report 29 Apr 2026

Dominic Yellezuome, University of Mines and Technology, Tarkwa, Western Region, Ghana

Approved with Reservations

https://doi.org/10.5256/f1000research.197955.r476295

The manuscript requires a thorough revision before it can be considered for acceptance.

The final sentence in the Methods section of the abstract should either be removed or integrated with the preceding sentence for better flow

The manuscript requires a thorough revision before it can be considered for acceptance.

The final sentence in the Methods section of the abstract should either be removed or integrated with the preceding sentence for better flow and clarity.
Several statements are supported by multiple references (three or more) without clearly justifying the relevance of each, and some cited works appear outdated. For example, the last sentence of the first paragraph of the Introduction.
The manuscript does not clearly articulate its scientific novelty in comparison to existing studies. This should be strengthened.
A proper reference should be provided for the rainfall and temperature data reported for Debre Markos.
In Subsection 2.5.1, the formula does not clearly indicate how the empty crucible is accounted for. Additionally, the explanation of variables should be formatted horizontally for consistency with the rest of the manuscript.
The authors indicated that subsection 2.5.4 has been deleted; however, this subsection still remains, which describes the same procedure as subsection 2.5.1.
In Section 2.6, “The 12 treatment types used for anaerobic co-digestion were cattle manure, fruit and vegetable waste, and cafeteria leftover food in mixtures of 1:1 ratio.” How do the three substrates have a mixing ratio of 1:1?
How is the information provided in Section 2.3 “After measuring the total solids (TS) of the samples, the de-sized cattle manure and food waste were mixed separately with distilled water in a 1:5 ratio (w/v) to maintain the total solid in the digester between 8 and 15%, which is the optimum value for wet anaerobic digestion (Ituen et al., 2007).” and Section 2.6 “Feed stock was mixed with distilled water to obtain approximately 8% of TS suspension.” different.
Section 2.7 “Anaerobic digesters (plastic bottles) were constructed for bench-scale experiments, in which biogas was produced from the degradation of substrates in a 0.6 L digester with a working volume of 450 mL.” Why use a different unit?
The retention time (duration) of anaerobic digestion is not specified in Section 2.7, despite being mentioned in the authors’ response. This information should be clearly included.
The control test was not described in the methodology section.
Figure 1 should be referenced in Section 2.7. Additionally, the experimental setup shown does not indicate that the digesters were maintained in an oven, which should be clarified. It is also recommended that Section 2.7 be presented before Section 2.6 for better logical flow.
Referencing Figure 1 again in Section 3.2 is unnecessary and can be removed.
Biogas production should be reported in terms of specific yield (e.g., mL/gVS or mL/gTS) to allow comparison with existing literature. The total solids or volatile solids before digestion are used for this assessment.
The response to the comment regarding the exclusion of rumen fluid (Table 2) is insufficient. The rationale for evaluating only the Saccharomyces cerevisiae isolate (MUTJ0F) instead of including rumen fluid should be clearly justified.
In Table 2, how relevant is the column containing MW₀ – MW₁₂?
Although the authors state that pH was monitored for 80 days to assess post-digestion stabilization, this was not included in the study objectives nor discussed in the Results and Discussion section. This inconsistency should be addressed.
What is the difference between Figure 1b and Figure 3a?
Some responses to reviewer comments lack clarity, making it difficult to understand the revisions made (e.g., Comments 31, 32 and 33). These responses should be improved for transparency.

Competing Interests: No competing interests were disclosed.

Reviewer Expertise: Anaerobic digestion, pyrolysis and gasification

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.

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Author Response 09 Jun 2026

Mulugeta Fentahun, College of Natural and Computational Sciences, Department of Biology, Debre Markos University, Debre Markos, 269, Ethiopia

09 Jun 2026

Author Response
Mulugeta Fentahun
Thanks to Dr. Dominic Yellezuome for your insightful comments and the time you dedicated to review our article.
I greatly appreciate your feedback and suggestions. Please find ... Continue reading
Mulugeta Fentahun
Thanks to Dr. Dominic Yellezuome for your insightful comments and the time you dedicated to review our article.
I greatly appreciate your feedback and suggestions. Please find our responses to your comments below:

Comment 1: The final sentence in the Methods section of the abstract should either be removed or integrated with the preceding sentence for better flow and clarity.

Response: Thank you for this valuable comment. We have revised the final sentence in the methods section of the abstract by integrating it with the preceding sentence to improve the flow, readability, and clarity of the abstract.

Comment 2: Several statements are supported by multiple references (three or more) without clearly justifying the relevance of each, and some cited works appear outdated. For example, the last sentence of the first paragraph of the Introduction.

Response: Thank you for this important observation. We have carefully reviewed the cited references throughout the manuscript. Redundant citations were reduced, and only the most relevant and recent references were retained to better support each statement.

Comment 3: The manuscript does not clearly articulate its scientific novelty in comparison to existing studies. This should be strengthened.

Response: Thank you for this constructive comment. We have strengthened the manuscript by clearly highlighting the scientific novelty and contribution of the study in the Introduction sections.

Comment 4: A proper reference should be provided for the rainfall and temperature data reported for Debre Markos.

Response: Thank you for this helpful comment. We have revised the manuscript to include appropriate references for the rainfall and temperature data reported for Debre Markos. Please refer to the materials and methods section under the study area description.

Comment 5: In Subsection 2.5.1, the formula does not clearly indicate how the empty crucible is accounted for. Additionally, the explanation of variables should be formatted horizontally for consistency with the rest of the manuscript.

Response: Thank you for this valuable comment. We have revised Subsection 2.5.1 to clearly indicate how the empty crucible weight was accounted for in the formula. In addition, the explanations of the variables used in the equation were reformatted horizontally to ensure consistency with the formatting style used throughout the manuscript.

Comment 6: The authors indicated that subsection 2.5.4 has been deleted; however, this subsection still remains, which describes the same procedure as subsection 2.5.1.

Response: Thank you for this important observation. We apologize for the oversight in the previous revision. The moisture content of each sample was determined using the oven-drying method, and the calculation was carried out using the formula provided in Subsection 2.5.4 (Moisture Content Determination).

Comment 7: In Section 2.6, “The 12 treatment types used for anaerobic co-digestion were cattle manure, fruit and vegetable waste, and cafeteria leftover food in mixtures of 1:1 ratio.” How do the three substrates have a mixing ratio of 1:1?

Response: Thank you for this important clarification. The correct mixing ratio for the three substrates is cafeteria leftover food, fruit and vegetable waste, and cattle manure in a 1:1:2 proportion, respectively. Section 2.6 has been revised to accurately reflect the three-substrate ratio.

Comment 8: How is the information provided in Section 2.3 “After measuring the total solids (TS) of the samples, the de-sized cattle manure and food waste were mixed separately with distilled water in a 1:5 ratio (w/v) to maintain the total solid in the digester between 8 and 15%, which is the optimum value for wet anaerobic digestion (Ituen et al., 2007).” and Section 2.6 “Feed stock was mixed with distilled water to obtain approximately 8% of TS suspension.” different.

Response: Thank you for this important observation. We acknowledge the inconsistency between the two sections of the methods. The manuscript has been revised by removing the repeated and overlapping content to ensure clarity and consistency between sections 2.3 and 2.7.

Comment 9: Section 2.7 “Anaerobic digesters (plastic bottles) were constructed for bench-scale experiments, in which biogas was produced from the degradation of substrates in a 0.6 L digester with a working volume of 450 mL.” Why use a different unit?

Response: Thank you for this important observation. The manuscript has been revised to ensure consistency in unit measurement.

Comment 10: The retention time (duration) of anaerobic digestion is not specified in Section 2.7, despite being mentioned in the authors’ response. This information should be clearly included.

Response: Thank you for this important observation. The manuscript has been revised to include the anaerobic digestion retention time in Section 2.6.

Comment 11: The control test was not described in the methodology section.

Response: Thank you for this important observation. The manuscript has been revised to include the control test in the methodology section. Please refer to the 2.7 experimental setup subsection in the methods section.

Comment 12: Figure 1 should be referenced in Section 2.7. Additionally, the experimental setup shown does not indicate that the digesters were maintained in an oven, which should be clarified. It is also recommended that Section 2.7 be presented before Section 2.6 for better logical flow.

Response: Thank you for this important observation. The manuscript has been revised accordingly. Figure 1 is now properly cited in the method section 2.6 Construction of the anaerobic digesters for batch system according to your comment. In addition, the experimental setup has been clarified to indicate that the digesters were maintained under controlled temperature conditions using an oven. Furthermore, the structure of the Methods section has been reorganized, with Section 2.7 now presented before Section 2.6 to improve the logical flow of the experimental description.

Comment 13: Referencing Figure 1 again in Section 3.2 is unnecessary and can be removed.

Response: Thank you for this helpful suggestion. We agree that repeating the reference to Figure 1 in Section 3.2 is unnecessary. The manuscript has been revised accordingly by removing the redundant citation to Figure 1 to avoid repetition.

Comment 14: Biogas production should be reported in terms of specific yield (e.g., mL/gVS or mL/gTS) to allow comparison with existing literature. The total solids or volatile solids before digestion are used for this assessment.

Response: Thank you for this important suggestion. We agree that reporting biogas production in terms of specific yield is essential for meaningful comparison with existing literature. The manuscript has been revised to present biogas production as biogas yield (mL/gVS), using the initial volatile solids (VS) content of the substrates prior to digestion as the basis for calculation. This improves the comparability and scientific rigor of the results. The Discussion section has also been revised accordingly. The comparison of the findings is mainly based on previous studies on enhancing biogas production from the co-digestion of organic wastes using rumen fluid as an inoculum only. However, studies combining both rumen fluid and Saccharomyces cerevisiae are limited in the literature, and therefore such combined inoculum effects were not discussed. The only relevant available study identified is Achmad KT, Gani SA, Sunarto SI, et al. (2011), The use of rumen liquid and Saccharomyces cerevisiae as activators in biogas production from fresh market garbage, Lucrări Ştiințifice, 56.

Comment 15: The response to the comment regarding the exclusion of rumen fluid (Table 2) is insufficient. The rationale for evaluating only the Saccharomyces cerevisiae isolate (MUTJ0F) instead of including rumen fluid should be clearly justified.

Response: Thank you for this important comment. The primary objective of the study was to evaluate the combined synergistic effect of the locally isolated Saccharomyces cerevisiae MUTJ0F strain in enhancing biogas production from mixed organic wastes under different rumen fluid supplementation levels. For this reason, all experimental treatments were designed to include the yeast strain while varying the amount of rumen fluid.

Comment 16: In Table 2, how relevant is the column containing MW0 – MW12?

Response: Thank you for this important comment. The manuscript has been revised by removing the column section from the Table 2 to avoid redundancy and improve clarity.

Comment 17: Although the authors state that pH was monitored for 80 days to assess post-digestion stabilization, this was not included in the study objectives nor discussed in the Results and Discussion section. This inconsistency should be addressed.

Response: Thank you for this important observation. We agree that the pH monitoring over 80 days was not clearly aligned with the stated objectives and was not sufficiently discussed in the Results and Discussion section. The manuscript has now been revised to address this inconsistency in the study objectives, methodology, and discussion section. The discussion has been expanded to explain pH variations in process stability and post-digestion stabilization in the digesters.

Comment 18: What is the difference between Figure 1b and Figure 3a?

Response: Figure 1b illustrates the complete experimental setup, including all functional components arranged for the anaerobic digestion process. In contrast, Figure 3a shows the digester bottles during the combustibility test, representing the practical application stage in which biogas production was evaluated through flame ignition. This figure was included to clearly demonstrate the combustibility of the biogas in a visible and understandable way for readers.

Comment 19: Some responses to reviewer comments lack clarity, making it difficult to understand the revisions made (e.g., Comments 31, 32 and 33). These responses should be improved for transparency.

Response: Thank you for this observation. We have carefully considered and addressed your comments. The revised version of the manuscript clearly describes the specific changes made, including the relevant sections.

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors
Mulugeta Fentahun
Thanks to Dr. Dominic Yellezuome for your insightful comments and the time you dedicated to review our article.
I greatly appreciate your feedback and suggestions. Please find our responses to your comments below:

Comment 1: The final sentence in the Methods section of the abstract should either be removed or integrated with the preceding sentence for better flow and clarity.

Response: Thank you for this valuable comment. We have revised the final sentence in the methods section of the abstract by integrating it with the preceding sentence to improve the flow, readability, and clarity of the abstract.

Comment 2: Several statements are supported by multiple references (three or more) without clearly justifying the relevance of each, and some cited works appear outdated. For example, the last sentence of the first paragraph of the Introduction.

Response: Thank you for this important observation. We have carefully reviewed the cited references throughout the manuscript. Redundant citations were reduced, and only the most relevant and recent references were retained to better support each statement.

Comment 3: The manuscript does not clearly articulate its scientific novelty in comparison to existing studies. This should be strengthened.

Response: Thank you for this constructive comment. We have strengthened the manuscript by clearly highlighting the scientific novelty and contribution of the study in the Introduction sections.

Comment 4: A proper reference should be provided for the rainfall and temperature data reported for Debre Markos.

Response: Thank you for this helpful comment. We have revised the manuscript to include appropriate references for the rainfall and temperature data reported for Debre Markos. Please refer to the materials and methods section under the study area description.

Comment 5: In Subsection 2.5.1, the formula does not clearly indicate how the empty crucible is accounted for. Additionally, the explanation of variables should be formatted horizontally for consistency with the rest of the manuscript.

Response: Thank you for this valuable comment. We have revised Subsection 2.5.1 to clearly indicate how the empty crucible weight was accounted for in the formula. In addition, the explanations of the variables used in the equation were reformatted horizontally to ensure consistency with the formatting style used throughout the manuscript.

Comment 6: The authors indicated that subsection 2.5.4 has been deleted; however, this subsection still remains, which describes the same procedure as subsection 2.5.1.

Response: Thank you for this important observation. We apologize for the oversight in the previous revision. The moisture content of each sample was determined using the oven-drying method, and the calculation was carried out using the formula provided in Subsection 2.5.4 (Moisture Content Determination).

Comment 7: In Section 2.6, “The 12 treatment types used for anaerobic co-digestion were cattle manure, fruit and vegetable waste, and cafeteria leftover food in mixtures of 1:1 ratio.” How do the three substrates have a mixing ratio of 1:1?

Response: Thank you for this important clarification. The correct mixing ratio for the three substrates is cafeteria leftover food, fruit and vegetable waste, and cattle manure in a 1:1:2 proportion, respectively. Section 2.6 has been revised to accurately reflect the three-substrate ratio.

Comment 8: How is the information provided in Section 2.3 “After measuring the total solids (TS) of the samples, the de-sized cattle manure and food waste were mixed separately with distilled water in a 1:5 ratio (w/v) to maintain the total solid in the digester between 8 and 15%, which is the optimum value for wet anaerobic digestion (Ituen et al., 2007).” and Section 2.6 “Feed stock was mixed with distilled water to obtain approximately 8% of TS suspension.” different.

Response: Thank you for this important observation. We acknowledge the inconsistency between the two sections of the methods. The manuscript has been revised by removing the repeated and overlapping content to ensure clarity and consistency between sections 2.3 and 2.7.

Comment 9: Section 2.7 “Anaerobic digesters (plastic bottles) were constructed for bench-scale experiments, in which biogas was produced from the degradation of substrates in a 0.6 L digester with a working volume of 450 mL.” Why use a different unit?

Response: Thank you for this important observation. The manuscript has been revised to ensure consistency in unit measurement.

Comment 10: The retention time (duration) of anaerobic digestion is not specified in Section 2.7, despite being mentioned in the authors’ response. This information should be clearly included.

Response: Thank you for this important observation. The manuscript has been revised to include the anaerobic digestion retention time in Section 2.6.

Comment 11: The control test was not described in the methodology section.

Response: Thank you for this important observation. The manuscript has been revised to include the control test in the methodology section. Please refer to the 2.7 experimental setup subsection in the methods section.

Comment 12: Figure 1 should be referenced in Section 2.7. Additionally, the experimental setup shown does not indicate that the digesters were maintained in an oven, which should be clarified. It is also recommended that Section 2.7 be presented before Section 2.6 for better logical flow.

Response: Thank you for this important observation. The manuscript has been revised accordingly. Figure 1 is now properly cited in the method section 2.6 Construction of the anaerobic digesters for batch system according to your comment. In addition, the experimental setup has been clarified to indicate that the digesters were maintained under controlled temperature conditions using an oven. Furthermore, the structure of the Methods section has been reorganized, with Section 2.7 now presented before Section 2.6 to improve the logical flow of the experimental description.

Comment 13: Referencing Figure 1 again in Section 3.2 is unnecessary and can be removed.

Response: Thank you for this helpful suggestion. We agree that repeating the reference to Figure 1 in Section 3.2 is unnecessary. The manuscript has been revised accordingly by removing the redundant citation to Figure 1 to avoid repetition.

Comment 14: Biogas production should be reported in terms of specific yield (e.g., mL/gVS or mL/gTS) to allow comparison with existing literature. The total solids or volatile solids before digestion are used for this assessment.

Response: Thank you for this important suggestion. We agree that reporting biogas production in terms of specific yield is essential for meaningful comparison with existing literature. The manuscript has been revised to present biogas production as biogas yield (mL/gVS), using the initial volatile solids (VS) content of the substrates prior to digestion as the basis for calculation. This improves the comparability and scientific rigor of the results. The Discussion section has also been revised accordingly. The comparison of the findings is mainly based on previous studies on enhancing biogas production from the co-digestion of organic wastes using rumen fluid as an inoculum only. However, studies combining both rumen fluid and Saccharomyces cerevisiae are limited in the literature, and therefore such combined inoculum effects were not discussed. The only relevant available study identified is Achmad KT, Gani SA, Sunarto SI, et al. (2011), The use of rumen liquid and Saccharomyces cerevisiae as activators in biogas production from fresh market garbage, Lucrări Ştiințifice, 56.

Comment 15: The response to the comment regarding the exclusion of rumen fluid (Table 2) is insufficient. The rationale for evaluating only the Saccharomyces cerevisiae isolate (MUTJ0F) instead of including rumen fluid should be clearly justified.

Response: Thank you for this important comment. The primary objective of the study was to evaluate the combined synergistic effect of the locally isolated Saccharomyces cerevisiae MUTJ0F strain in enhancing biogas production from mixed organic wastes under different rumen fluid supplementation levels. For this reason, all experimental treatments were designed to include the yeast strain while varying the amount of rumen fluid.

Comment 16: In Table 2, how relevant is the column containing MW0 – MW12?

Response: Thank you for this important comment. The manuscript has been revised by removing the column section from the Table 2 to avoid redundancy and improve clarity.

Comment 17: Although the authors state that pH was monitored for 80 days to assess post-digestion stabilization, this was not included in the study objectives nor discussed in the Results and Discussion section. This inconsistency should be addressed.

Response: Thank you for this important observation. We agree that the pH monitoring over 80 days was not clearly aligned with the stated objectives and was not sufficiently discussed in the Results and Discussion section. The manuscript has now been revised to address this inconsistency in the study objectives, methodology, and discussion section. The discussion has been expanded to explain pH variations in process stability and post-digestion stabilization in the digesters.

Comment 18: What is the difference between Figure 1b and Figure 3a?

Response: Figure 1b illustrates the complete experimental setup, including all functional components arranged for the anaerobic digestion process. In contrast, Figure 3a shows the digester bottles during the combustibility test, representing the practical application stage in which biogas production was evaluated through flame ignition. This figure was included to clearly demonstrate the combustibility of the biogas in a visible and understandable way for readers.

Comment 19: Some responses to reviewer comments lack clarity, making it difficult to understand the revisions made (e.g., Comments 31, 32 and 33). These responses should be improved for transparency.

Response: Thank you for this observation. We have carefully considered and addressed your comments. The revised version of the manuscript clearly describes the specific changes made, including the relevant sections.

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors
Competing Interests: No competing interests were disclosed. Close
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COMMENTS ON THIS REPORT

Author Response 09 Jun 2026

Mulugeta Fentahun, College of Natural and Computational Sciences, Department of Biology, Debre Markos University, Debre Markos, 269, Ethiopia

09 Jun 2026

Author Response
Mulugeta Fentahun
Thanks to Dr. Dominic Yellezuome for your insightful comments and the time you dedicated to review our article.
I greatly appreciate your feedback and suggestions. Please find ... Continue reading
Mulugeta Fentahun
Thanks to Dr. Dominic Yellezuome for your insightful comments and the time you dedicated to review our article.
I greatly appreciate your feedback and suggestions. Please find our responses to your comments below:

Comment 1: The final sentence in the Methods section of the abstract should either be removed or integrated with the preceding sentence for better flow and clarity.

Response: Thank you for this valuable comment. We have revised the final sentence in the methods section of the abstract by integrating it with the preceding sentence to improve the flow, readability, and clarity of the abstract.

Comment 2: Several statements are supported by multiple references (three or more) without clearly justifying the relevance of each, and some cited works appear outdated. For example, the last sentence of the first paragraph of the Introduction.

Response: Thank you for this important observation. We have carefully reviewed the cited references throughout the manuscript. Redundant citations were reduced, and only the most relevant and recent references were retained to better support each statement.

Comment 3: The manuscript does not clearly articulate its scientific novelty in comparison to existing studies. This should be strengthened.

Response: Thank you for this constructive comment. We have strengthened the manuscript by clearly highlighting the scientific novelty and contribution of the study in the Introduction sections.

Comment 4: A proper reference should be provided for the rainfall and temperature data reported for Debre Markos.

Response: Thank you for this helpful comment. We have revised the manuscript to include appropriate references for the rainfall and temperature data reported for Debre Markos. Please refer to the materials and methods section under the study area description.

Comment 5: In Subsection 2.5.1, the formula does not clearly indicate how the empty crucible is accounted for. Additionally, the explanation of variables should be formatted horizontally for consistency with the rest of the manuscript.

Response: Thank you for this valuable comment. We have revised Subsection 2.5.1 to clearly indicate how the empty crucible weight was accounted for in the formula. In addition, the explanations of the variables used in the equation were reformatted horizontally to ensure consistency with the formatting style used throughout the manuscript.

Comment 6: The authors indicated that subsection 2.5.4 has been deleted; however, this subsection still remains, which describes the same procedure as subsection 2.5.1.

Response: Thank you for this important observation. We apologize for the oversight in the previous revision. The moisture content of each sample was determined using the oven-drying method, and the calculation was carried out using the formula provided in Subsection 2.5.4 (Moisture Content Determination).

Comment 7: In Section 2.6, “The 12 treatment types used for anaerobic co-digestion were cattle manure, fruit and vegetable waste, and cafeteria leftover food in mixtures of 1:1 ratio.” How do the three substrates have a mixing ratio of 1:1?

Response: Thank you for this important clarification. The correct mixing ratio for the three substrates is cafeteria leftover food, fruit and vegetable waste, and cattle manure in a 1:1:2 proportion, respectively. Section 2.6 has been revised to accurately reflect the three-substrate ratio.

Comment 8: How is the information provided in Section 2.3 “After measuring the total solids (TS) of the samples, the de-sized cattle manure and food waste were mixed separately with distilled water in a 1:5 ratio (w/v) to maintain the total solid in the digester between 8 and 15%, which is the optimum value for wet anaerobic digestion (Ituen et al., 2007).” and Section 2.6 “Feed stock was mixed with distilled water to obtain approximately 8% of TS suspension.” different.

Response: Thank you for this important observation. We acknowledge the inconsistency between the two sections of the methods. The manuscript has been revised by removing the repeated and overlapping content to ensure clarity and consistency between sections 2.3 and 2.7.

Comment 9: Section 2.7 “Anaerobic digesters (plastic bottles) were constructed for bench-scale experiments, in which biogas was produced from the degradation of substrates in a 0.6 L digester with a working volume of 450 mL.” Why use a different unit?

Response: Thank you for this important observation. The manuscript has been revised to ensure consistency in unit measurement.

Comment 10: The retention time (duration) of anaerobic digestion is not specified in Section 2.7, despite being mentioned in the authors’ response. This information should be clearly included.

Response: Thank you for this important observation. The manuscript has been revised to include the anaerobic digestion retention time in Section 2.6.

Comment 11: The control test was not described in the methodology section.

Response: Thank you for this important observation. The manuscript has been revised to include the control test in the methodology section. Please refer to the 2.7 experimental setup subsection in the methods section.

Comment 12: Figure 1 should be referenced in Section 2.7. Additionally, the experimental setup shown does not indicate that the digesters were maintained in an oven, which should be clarified. It is also recommended that Section 2.7 be presented before Section 2.6 for better logical flow.

Response: Thank you for this important observation. The manuscript has been revised accordingly. Figure 1 is now properly cited in the method section 2.6 Construction of the anaerobic digesters for batch system according to your comment. In addition, the experimental setup has been clarified to indicate that the digesters were maintained under controlled temperature conditions using an oven. Furthermore, the structure of the Methods section has been reorganized, with Section 2.7 now presented before Section 2.6 to improve the logical flow of the experimental description.

Comment 13: Referencing Figure 1 again in Section 3.2 is unnecessary and can be removed.

Response: Thank you for this helpful suggestion. We agree that repeating the reference to Figure 1 in Section 3.2 is unnecessary. The manuscript has been revised accordingly by removing the redundant citation to Figure 1 to avoid repetition.

Comment 14: Biogas production should be reported in terms of specific yield (e.g., mL/gVS or mL/gTS) to allow comparison with existing literature. The total solids or volatile solids before digestion are used for this assessment.

Response: Thank you for this important suggestion. We agree that reporting biogas production in terms of specific yield is essential for meaningful comparison with existing literature. The manuscript has been revised to present biogas production as biogas yield (mL/gVS), using the initial volatile solids (VS) content of the substrates prior to digestion as the basis for calculation. This improves the comparability and scientific rigor of the results. The Discussion section has also been revised accordingly. The comparison of the findings is mainly based on previous studies on enhancing biogas production from the co-digestion of organic wastes using rumen fluid as an inoculum only. However, studies combining both rumen fluid and Saccharomyces cerevisiae are limited in the literature, and therefore such combined inoculum effects were not discussed. The only relevant available study identified is Achmad KT, Gani SA, Sunarto SI, et al. (2011), The use of rumen liquid and Saccharomyces cerevisiae as activators in biogas production from fresh market garbage, Lucrări Ştiințifice, 56.

Comment 15: The response to the comment regarding the exclusion of rumen fluid (Table 2) is insufficient. The rationale for evaluating only the Saccharomyces cerevisiae isolate (MUTJ0F) instead of including rumen fluid should be clearly justified.

Response: Thank you for this important comment. The primary objective of the study was to evaluate the combined synergistic effect of the locally isolated Saccharomyces cerevisiae MUTJ0F strain in enhancing biogas production from mixed organic wastes under different rumen fluid supplementation levels. For this reason, all experimental treatments were designed to include the yeast strain while varying the amount of rumen fluid.

Comment 16: In Table 2, how relevant is the column containing MW0 – MW12?

Response: Thank you for this important comment. The manuscript has been revised by removing the column section from the Table 2 to avoid redundancy and improve clarity.

Comment 17: Although the authors state that pH was monitored for 80 days to assess post-digestion stabilization, this was not included in the study objectives nor discussed in the Results and Discussion section. This inconsistency should be addressed.

Response: Thank you for this important observation. We agree that the pH monitoring over 80 days was not clearly aligned with the stated objectives and was not sufficiently discussed in the Results and Discussion section. The manuscript has now been revised to address this inconsistency in the study objectives, methodology, and discussion section. The discussion has been expanded to explain pH variations in process stability and post-digestion stabilization in the digesters.

Comment 18: What is the difference between Figure 1b and Figure 3a?

Response: Figure 1b illustrates the complete experimental setup, including all functional components arranged for the anaerobic digestion process. In contrast, Figure 3a shows the digester bottles during the combustibility test, representing the practical application stage in which biogas production was evaluated through flame ignition. This figure was included to clearly demonstrate the combustibility of the biogas in a visible and understandable way for readers.

Comment 19: Some responses to reviewer comments lack clarity, making it difficult to understand the revisions made (e.g., Comments 31, 32 and 33). These responses should be improved for transparency.

Response: Thank you for this observation. We have carefully considered and addressed your comments. The revised version of the manuscript clearly describes the specific changes made, including the relevant sections.

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors
Mulugeta Fentahun
Thanks to Dr. Dominic Yellezuome for your insightful comments and the time you dedicated to review our article.
I greatly appreciate your feedback and suggestions. Please find our responses to your comments below:

Comment 1: The final sentence in the Methods section of the abstract should either be removed or integrated with the preceding sentence for better flow and clarity.

Response: Thank you for this valuable comment. We have revised the final sentence in the methods section of the abstract by integrating it with the preceding sentence to improve the flow, readability, and clarity of the abstract.

Comment 2: Several statements are supported by multiple references (three or more) without clearly justifying the relevance of each, and some cited works appear outdated. For example, the last sentence of the first paragraph of the Introduction.

Response: Thank you for this important observation. We have carefully reviewed the cited references throughout the manuscript. Redundant citations were reduced, and only the most relevant and recent references were retained to better support each statement.

Comment 3: The manuscript does not clearly articulate its scientific novelty in comparison to existing studies. This should be strengthened.

Response: Thank you for this constructive comment. We have strengthened the manuscript by clearly highlighting the scientific novelty and contribution of the study in the Introduction sections.

Comment 4: A proper reference should be provided for the rainfall and temperature data reported for Debre Markos.

Response: Thank you for this helpful comment. We have revised the manuscript to include appropriate references for the rainfall and temperature data reported for Debre Markos. Please refer to the materials and methods section under the study area description.

Comment 5: In Subsection 2.5.1, the formula does not clearly indicate how the empty crucible is accounted for. Additionally, the explanation of variables should be formatted horizontally for consistency with the rest of the manuscript.

Response: Thank you for this valuable comment. We have revised Subsection 2.5.1 to clearly indicate how the empty crucible weight was accounted for in the formula. In addition, the explanations of the variables used in the equation were reformatted horizontally to ensure consistency with the formatting style used throughout the manuscript.

Comment 6: The authors indicated that subsection 2.5.4 has been deleted; however, this subsection still remains, which describes the same procedure as subsection 2.5.1.

Response: Thank you for this important observation. We apologize for the oversight in the previous revision. The moisture content of each sample was determined using the oven-drying method, and the calculation was carried out using the formula provided in Subsection 2.5.4 (Moisture Content Determination).

Comment 7: In Section 2.6, “The 12 treatment types used for anaerobic co-digestion were cattle manure, fruit and vegetable waste, and cafeteria leftover food in mixtures of 1:1 ratio.” How do the three substrates have a mixing ratio of 1:1?

Response: Thank you for this important clarification. The correct mixing ratio for the three substrates is cafeteria leftover food, fruit and vegetable waste, and cattle manure in a 1:1:2 proportion, respectively. Section 2.6 has been revised to accurately reflect the three-substrate ratio.

Comment 8: How is the information provided in Section 2.3 “After measuring the total solids (TS) of the samples, the de-sized cattle manure and food waste were mixed separately with distilled water in a 1:5 ratio (w/v) to maintain the total solid in the digester between 8 and 15%, which is the optimum value for wet anaerobic digestion (Ituen et al., 2007).” and Section 2.6 “Feed stock was mixed with distilled water to obtain approximately 8% of TS suspension.” different.

Response: Thank you for this important observation. We acknowledge the inconsistency between the two sections of the methods. The manuscript has been revised by removing the repeated and overlapping content to ensure clarity and consistency between sections 2.3 and 2.7.

Comment 9: Section 2.7 “Anaerobic digesters (plastic bottles) were constructed for bench-scale experiments, in which biogas was produced from the degradation of substrates in a 0.6 L digester with a working volume of 450 mL.” Why use a different unit?

Response: Thank you for this important observation. The manuscript has been revised to ensure consistency in unit measurement.

Comment 10: The retention time (duration) of anaerobic digestion is not specified in Section 2.7, despite being mentioned in the authors’ response. This information should be clearly included.

Response: Thank you for this important observation. The manuscript has been revised to include the anaerobic digestion retention time in Section 2.6.

Comment 11: The control test was not described in the methodology section.

Response: Thank you for this important observation. The manuscript has been revised to include the control test in the methodology section. Please refer to the 2.7 experimental setup subsection in the methods section.

Comment 12: Figure 1 should be referenced in Section 2.7. Additionally, the experimental setup shown does not indicate that the digesters were maintained in an oven, which should be clarified. It is also recommended that Section 2.7 be presented before Section 2.6 for better logical flow.

Response: Thank you for this important observation. The manuscript has been revised accordingly. Figure 1 is now properly cited in the method section 2.6 Construction of the anaerobic digesters for batch system according to your comment. In addition, the experimental setup has been clarified to indicate that the digesters were maintained under controlled temperature conditions using an oven. Furthermore, the structure of the Methods section has been reorganized, with Section 2.7 now presented before Section 2.6 to improve the logical flow of the experimental description.

Comment 13: Referencing Figure 1 again in Section 3.2 is unnecessary and can be removed.

Response: Thank you for this helpful suggestion. We agree that repeating the reference to Figure 1 in Section 3.2 is unnecessary. The manuscript has been revised accordingly by removing the redundant citation to Figure 1 to avoid repetition.

Comment 14: Biogas production should be reported in terms of specific yield (e.g., mL/gVS or mL/gTS) to allow comparison with existing literature. The total solids or volatile solids before digestion are used for this assessment.

Response: Thank you for this important suggestion. We agree that reporting biogas production in terms of specific yield is essential for meaningful comparison with existing literature. The manuscript has been revised to present biogas production as biogas yield (mL/gVS), using the initial volatile solids (VS) content of the substrates prior to digestion as the basis for calculation. This improves the comparability and scientific rigor of the results. The Discussion section has also been revised accordingly. The comparison of the findings is mainly based on previous studies on enhancing biogas production from the co-digestion of organic wastes using rumen fluid as an inoculum only. However, studies combining both rumen fluid and Saccharomyces cerevisiae are limited in the literature, and therefore such combined inoculum effects were not discussed. The only relevant available study identified is Achmad KT, Gani SA, Sunarto SI, et al. (2011), The use of rumen liquid and Saccharomyces cerevisiae as activators in biogas production from fresh market garbage, Lucrări Ştiințifice, 56.

Comment 15: The response to the comment regarding the exclusion of rumen fluid (Table 2) is insufficient. The rationale for evaluating only the Saccharomyces cerevisiae isolate (MUTJ0F) instead of including rumen fluid should be clearly justified.

Response: Thank you for this important comment. The primary objective of the study was to evaluate the combined synergistic effect of the locally isolated Saccharomyces cerevisiae MUTJ0F strain in enhancing biogas production from mixed organic wastes under different rumen fluid supplementation levels. For this reason, all experimental treatments were designed to include the yeast strain while varying the amount of rumen fluid.

Comment 16: In Table 2, how relevant is the column containing MW0 – MW12?

Response: Thank you for this important comment. The manuscript has been revised by removing the column section from the Table 2 to avoid redundancy and improve clarity.

Comment 17: Although the authors state that pH was monitored for 80 days to assess post-digestion stabilization, this was not included in the study objectives nor discussed in the Results and Discussion section. This inconsistency should be addressed.

Response: Thank you for this important observation. We agree that the pH monitoring over 80 days was not clearly aligned with the stated objectives and was not sufficiently discussed in the Results and Discussion section. The manuscript has now been revised to address this inconsistency in the study objectives, methodology, and discussion section. The discussion has been expanded to explain pH variations in process stability and post-digestion stabilization in the digesters.

Comment 18: What is the difference between Figure 1b and Figure 3a?

Response: Figure 1b illustrates the complete experimental setup, including all functional components arranged for the anaerobic digestion process. In contrast, Figure 3a shows the digester bottles during the combustibility test, representing the practical application stage in which biogas production was evaluated through flame ignition. This figure was included to clearly demonstrate the combustibility of the biogas in a visible and understandable way for readers.

Comment 19: Some responses to reviewer comments lack clarity, making it difficult to understand the revisions made (e.g., Comments 31, 32 and 33). These responses should be improved for transparency.

Response: Thank you for this observation. We have carefully considered and addressed your comments. The revised version of the manuscript clearly describes the specific changes made, including the relevant sections.

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors
Competing Interests: No competing interests were disclosed. Close
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Version 2

VERSION 2

PUBLISHED 19 Dec 2025

Revised

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Reviewer Report 13 Jan 2026

Josef Marousek, Technical University of Košice, Košice–Sever, Slovakia

Not Approved

https://doi.org/10.5256/f1000research.193404.r449755

The urgency and significance of the research hypothesis needs to be better justified and placed into [economic/industrial/environmental] context. It is appropriate to adapt he methodology to the current state of knowledge. The applicability needs to be strenghtened [cost breakdown and ... Continue reading

Is the work clearly and accurately presented and does it cite the current literature?

No
Is the study design appropriate and is the work technically sound?

Partly
Are sufficient details of methods and analysis provided to allow replication by others?

Partly
If applicable, is the statistical analysis and its interpretation appropriate?

Partly
Are all the source data underlying the results available to ensure full reproducibility?

No
Are the conclusions drawn adequately supported by the results?

No

Competing Interests: No competing interests were disclosed.

Reviewer Expertise: phytotechnology, commercialization

I confirm that I have read this submission and believe that I have an appropriate level of expertise to state that I do not consider it to be of an acceptable scientific standard, for reasons outlined above.

CITE

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Author Response 18 Apr 2026

Mulugeta Fentahun, College of Natural and Computational Sciences, Department of Biology, Debre Markos University, Debre Markos, 269, Ethiopia

18 Apr 2026

Author Response
Mulugeta Fentahun
Professor Josef Marousek thank you very much for your insightful comments and the time you dedicated to review our article.
I greatly appreciate your feedback and suggestions. ... Continue reading
Mulugeta Fentahun
Professor Josef Marousek thank you very much for your insightful comments and the time you dedicated to review our article.
I greatly appreciate your feedback and suggestions. Please find my responses to your comments below:

Comment1: The urgency and significance of the research hypothesis needs to be better justified and placed into [economic/industrial/environmental] context.

Response: Thank you for this valuable comment. We have revised the manuscript to better clarify the urgency and significance of the research hypothesis within economic, industrial, and environmental contexts. Refer to the introduction part of the updated manuscript.

Comment2: It is appropriate to adapt the methodology to the current state of knowledge

Response: Thank you for this helpful comment. We have revised the methodology to align with the current state of knowledge by updating the experimental method based on recent literature. Refer to the method section of the updated manuscript.

Comment3: The applicability needs to be strengthened [cost breakdown and corresponding financial analyses are hard to find].

Response: Thank you for this important comment. We have strengthened the applicability of the study by considering the economic feasibility and practical potential of the study.

Comment4: It is advisable to improve the conclusions in terms of synthesis and fertilization.

Response: Thank you for this valuable suggestion. We have revised the conclusion section (refer to the revised manuscript).

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors
Mulugeta Fentahun
Professor Josef Marousek thank you very much for your insightful comments and the time you dedicated to review our article.
I greatly appreciate your feedback and suggestions. Please find my responses to your comments below:

Comment1: The urgency and significance of the research hypothesis needs to be better justified and placed into [economic/industrial/environmental] context.

Response: Thank you for this valuable comment. We have revised the manuscript to better clarify the urgency and significance of the research hypothesis within economic, industrial, and environmental contexts. Refer to the introduction part of the updated manuscript.

Comment2: It is appropriate to adapt the methodology to the current state of knowledge

Response: Thank you for this helpful comment. We have revised the methodology to align with the current state of knowledge by updating the experimental method based on recent literature. Refer to the method section of the updated manuscript.

Comment3: The applicability needs to be strengthened [cost breakdown and corresponding financial analyses are hard to find].

Response: Thank you for this important comment. We have strengthened the applicability of the study by considering the economic feasibility and practical potential of the study.

Comment4: It is advisable to improve the conclusions in terms of synthesis and fertilization.

Response: Thank you for this valuable suggestion. We have revised the conclusion section (refer to the revised manuscript).

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors
Competing Interests: No competing interests were disclosed. Close
Report a concern
Respond or Comment

COMMENTS ON THIS REPORT

Author Response 18 Apr 2026

Mulugeta Fentahun, College of Natural and Computational Sciences, Department of Biology, Debre Markos University, Debre Markos, 269, Ethiopia

18 Apr 2026

Author Response
Mulugeta Fentahun
Professor Josef Marousek thank you very much for your insightful comments and the time you dedicated to review our article.
I greatly appreciate your feedback and suggestions. ... Continue reading
Mulugeta Fentahun
Professor Josef Marousek thank you very much for your insightful comments and the time you dedicated to review our article.
I greatly appreciate your feedback and suggestions. Please find my responses to your comments below:

Comment1: The urgency and significance of the research hypothesis needs to be better justified and placed into [economic/industrial/environmental] context.

Response: Thank you for this valuable comment. We have revised the manuscript to better clarify the urgency and significance of the research hypothesis within economic, industrial, and environmental contexts. Refer to the introduction part of the updated manuscript.

Comment2: It is appropriate to adapt the methodology to the current state of knowledge

Response: Thank you for this helpful comment. We have revised the methodology to align with the current state of knowledge by updating the experimental method based on recent literature. Refer to the method section of the updated manuscript.

Comment3: The applicability needs to be strengthened [cost breakdown and corresponding financial analyses are hard to find].

Response: Thank you for this important comment. We have strengthened the applicability of the study by considering the economic feasibility and practical potential of the study.

Comment4: It is advisable to improve the conclusions in terms of synthesis and fertilization.

Response: Thank you for this valuable suggestion. We have revised the conclusion section (refer to the revised manuscript).

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors
Mulugeta Fentahun
Professor Josef Marousek thank you very much for your insightful comments and the time you dedicated to review our article.
I greatly appreciate your feedback and suggestions. Please find my responses to your comments below:

Comment1: The urgency and significance of the research hypothesis needs to be better justified and placed into [economic/industrial/environmental] context.

Response: Thank you for this valuable comment. We have revised the manuscript to better clarify the urgency and significance of the research hypothesis within economic, industrial, and environmental contexts. Refer to the introduction part of the updated manuscript.

Comment2: It is appropriate to adapt the methodology to the current state of knowledge

Response: Thank you for this helpful comment. We have revised the methodology to align with the current state of knowledge by updating the experimental method based on recent literature. Refer to the method section of the updated manuscript.

Comment3: The applicability needs to be strengthened [cost breakdown and corresponding financial analyses are hard to find].

Response: Thank you for this important comment. We have strengthened the applicability of the study by considering the economic feasibility and practical potential of the study.

Comment4: It is advisable to improve the conclusions in terms of synthesis and fertilization.

Response: Thank you for this valuable suggestion. We have revised the conclusion section (refer to the revised manuscript).

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors
Competing Interests: No competing interests were disclosed. Close
Report a concern

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Reviewer Report 09 Jan 2026

Dominic Yellezuome, University of Mines and Technology, Tarkwa, Western Region, Ghana

Approved with Reservations

https://doi.org/10.5256/f1000research.193404.r445154

This manuscript aimed at enhancing biogas production from a co-digestion of various organic wastes using rumen fluid and Saccharomyces cerevisiae isolate MUTJ0F as activators. The manuscript requires a careful major revision before it could possibly be accepted.
... Continue reading

There is too much information in the methods paragraph in the Abstract Section, in which some of it can not be found in the Methods Section, such as “This study was conducted experimentally using factorial patterns and a completely randomized 6 × 2 design.”
And some of them are not important to be in the Abstract Section. Such as “Standard techniques were used to measure the physicochemical characteristics of the mixed waste, such as pH, total solids, volatile solids, organic carbon, and moisture. This study was conducted experimentally using factorial patterns and a completely randomized 6 × 2 design. The water displacement method was used to estimate the average amount of biogas generated by a 0.6 L digester.”
These sentences are similar; hence should be merged.

“Biogas production from different types of biodegradable waste is an alternative to fossil fuels for energy consumption and biodegradable waste management. Biogas is a cost-effective, environmentally friendly, and sustainable energy source that provides a reliable method for handling food waste.”
“An innovative solution to increase anaerobic waste digestion yields is codigestion, which is an inexpensive and simple technology that enhances the anaerobic digestion rate by creating a better nutrient balance from the materials mixed to feed the digester, provides positive synergism for bacterial growth, and increases biogas production (Sosnowski et al., 2003; Mata-Alvarez et al., 2000; Mshandete et al., 2004; Leta et al., 2015). Several studies have used co-digestion to increase the rate at which organic matter is converted biologically in the biogas system to improve biogas performance (Huang et al., 2016; Alemayehu, 2014; Mata-Alvarez et al., 2014; Abbas et al., 2021).”
“A diverse range of fungi, bacteria, protozoa, and archaea inhabit the rumen, an anaerobic microbial habitat (Sylvester et al., 2004; Sonakya et al., 2003). The rumen contains a variety of microorganisms, including cellulolytic and methanogenic bacteria (Lopes et al., 2004; Yue and Yu, 2009).”
“Institutions such as universities, agro-industries, and municipalities that produce large amounts of food and fruit-vegetable waste should implement co-digestion systems using these inoculants to improve waste management, lower environmental pollution, and produce renewable energy. Additionally, by offering a cleaner, sustainable alternative for household and industrial energy, expanding this strategy could improve public health, reduce reliance on firewood, and mitigate deforestation.”

Authors cited lists of 3 or more references without proper justification of the relevance of each one. Hence, avoid citing more than two references and outdated references.
“Although there is information on biogas production from organic waste or single inoculums (Alemayehu, 2014; Abayneh et al., 2014; Hammad et al., 2018; Earnest and Singh, 2013) but there is limited reports on methods for increasing biogas generation, particularly those that use rumen fluid and S. cerevisiae.” This paper is not clear in the description of the scientific novelty in comparison to related previously published and referenced in your work below:

Achmad KT, Gani SA, Sunarto SI, et al.: The use of rumen liquid and Saccharomyces cerevisiae as activators in biogas production from fresh market garbage. Lucrări Ştiinţifice. 2011; 56.

Aragaw T, Mebeaselassie A, Amare G: Co-digestion of cattle manure with organic kitchen waste to increase biogas production using rumen fluid as inoculums. International Journal of the Physical Sciences. 2013; 8: 443–450.

Tamirat A, Mebeaselassie A, Amare G: Co-digestion of cattle manure with organic kitchen waste to increase biogas production using rumen fluid as inoculums. International Journal of Physical Sciences. 2013; 8: 443–450.

Tamrat A: Effects of Co-Digestion of Cattle Manure with Organic Kitchen Waste Using Rumen Fluid as Inoculums on the Rate and Amount of Biogas Yield. Haramaya university; 2012. Master’s thesis

Yue ZB, Yu HQ: Anaerobic batch degradation of cattail by rumen cultures. International Journal of Environmental Pollution. 2009; 38: 299–308.

Zhang H, Zhang P, Ye J, et al.: Improvement of methane production from rice straw with rumen fluid pretreatment: A feasibility study. International Biodeterioration & Biodegradation. 2016; 113: 9–16.

“…there are 107,684 residents, comprising 49,893 men and 57,791 women (Aynalem et al., 2014).” These statistics are outdated.
“This study aimed to evaluate the effects of ruminant fluids and S. cerevisiae isolate MUTJ0F (OR209280.1) on biogas generation from various mixed organic wastes co-digested with cattle manure. Various wastes from fruits and vegetables were gathered from the town fruit houses, leftover food from the Debre Markos University student cafeteria, fresh cattle manure (CM) from Monkorer Agroindustry Enterprise, and rumen fluids (RL) from a nearby slaughterhouse and used as activators for biogas production.” These sentences contains repititions in the next paragraph, hence should be avoided.
“… the de-sized cattle manure and food waste were mixed separately with distilled water in a 1:5 (solid waste: distilled water) volume ratio …” What is the ratio between cafeteria leftovers, cattle manure, and fruit and vegetable waste? How was the solid waste measured in volume?
What is the size of the filter used in filtering the rumen fluid?
Some of the citations are not necessary, such as

“Then, different amounts of the filtrate were added to each digester to initiate the reaction (Aurora, 1983; Genet et al., 2018).”
“After calibration, the electrode was submerged in the substrate samples, rinsed with distilled water, and the pH values were recorded (Arogo et al., 2009).”

In subsection 2.5.1, how was the measured empty crucible used in the formula?
In subsection 2.5.2, the authors indicated the measurement of fixed solids, but it was not presented in Table 1.
Authors should be consistent with the way they explain parameters in an equation, whether horizontal or vertical.
The procedure for moisture content determination is the same as that of total solids, so you can indicate the formula of MC there and delete subsection 2.5.4
“After calibration, the electrode was submerged in the substrate samples, rinsed with distilled water, and the pH values were recorded (Arogo et al., 2009).” Are the authors sure this was the sequence used in measuring the pH value?
“The first factor was the dosage of rumen liquid i.e. 0 ml/100 g, 25 ml/100 g, 50 ml/100 g, 75 ml/100 g, and 100 ml/100 g), …” Why is the 150 ml rumen fluid not stated here but in Table 2?
“The study was conducted at room temperature (30°C).” How did the authors maintain this temperature in the room?
“Feed stock was mixed with distilled water to obtain approximately 8% of TS suspension.” Is this information similar to the “1:5 (solid waste: distilled water) volume ratio” indicated in Section 2.3?
In section 2.6, the retention time or duration of the anaerobic digestion was not mentioned.
Section 2.7 should come before Section 2.6. Also, the authors need to provide an image of the three plastic bottles set up for anaerobic digestion, since it was constructed for this study. What is the working volume of the digester?
Sections 2.8 and 2.7 can be merged. Was the biogas measured daily or at what interval?
In Section 3.1, what does the use of “mixed wastes” mean? For example: “The pH of the mixed waste ranged from 6.8 to 7.6, …” Does it mean the mixture of the various feedstock or the individual feedstock?
“The VS/TS ratios of the cafeteria food waste and cattle manure were 78.3% and 91.2%, respectively.” What about fruit and vegetable waste?
“Cattle dung is used to accelerate biogas production by promoting bacterial growth in the digester.” Provide a reference.
“Co-digestion has a positive synergistic effect by neutralizing pH, increasing buffering capacity, reducing the effects of harmful compounds, and supplying more balanced nutrients, such as vitamins, trace metals, and other substances required for microbial growth (Fang, 2010; Aragaw et al., 2013; Jianzheng et al., 2011).” The relevance of this information in the Results and Discussion Section is not clear since it has already been stated in the Introduction Section with different references cited.
“The 12 methane production treatments varied significantly, reflecting variations in the mixed-waste composition and inoculum dosage.” Are the authors sure that the variations in the mixed-waste composition may have caused the significant difference in biogas production?
“This implies that the high anaerobic bacterial concentration in rumen fluid efficiently breaks down organic substrates from mixed waste.” Is it only the rumen fluid that increased biogas production?
“According to the results, the maximum amount of biogas (6900.3 ml) …” Normally, biogas production is evaluated using methane yield (mL/gVS or mL/gTS) to enable comparison with other published studies.
In Table 2, why was only rumen fluid not investigated? The heading “Methane (mean ± SD)”, did the authors measure methane or biogas?
In Figure 1, please plot pH on the y-axis and days on the x-axis. Why plot only T10? It is better to plot all the treatments. Why was the pH measured up to 80 days, but the anaerobic digestion was observed for 60 days, as indicated in Figure 2, the Abstract and Section 3.4?
Figure 2A and B should come before Figure 1.
These sentences could have been verified by plotting the daily biogas production.

“This low pH value was permitted very little methanogenic bacterial activity …”
“This also brings the pH closer to neutral, which makes it easier for methanogenic microbes to multiply and produce methane. Methanogenic bacteria the optimum pH values between 6.8 and 7.2 (Anunputtikul and Rodtong, 2004; Budiyono et al., 2010).”

The authors should clarify which equipment was used for the combustion test, either “a lit matchstick” as indicated in Section 2.9 or “a Bunsen burner” as indicated in Section 3.4. Also, Figure 2C was not well captured to help identify which equipment was used. In section 3.4, it is better use “Figure 2C” rather than “Figure 2”.
“Biodegradation, microbial strength, and biogas generation can all be enhanced by using …” How were biodegradation and microbial strength measured in this study?
Future perspectives or studies could be added to the Conclusion section.
The language must be checked thoroughly.

Some statements are not clear or too long and should be revised. For examples:

“However, various juice house wastes are among the municipal wastes that are becoming difficult to manage.” Also, indicate why they are difficult to manage.

“… food waste co-digestion under anaerobic conditions and cattle manure, …”

“The strain Saccharomyces cerevisiae isolate MUTJ0F (OR209280.1) with accession number was used in this study.”

“A mixture of substrates, including peels of bread, injera, spaghetti, papaya, mango, banana, and avocado was used in this study.” Which substrates?

“The CM was separated …” Should it be “separated” or “spread”?

“The inoculum was specific to each digester.”

“The crucibles were dried, cooled to room temperature in a desiccator, and weighed again.” Should it be “dried” or “removed”?

“According to Haug (1993), using data from volatile solids and an empirical equation, the organic carbon was calculated, and the organic carbon content of the sample was calculated by taking into account the volatile solids content, which was expressed as a percentage:”

“The first factor was the dosage of rumen liquid i.e. 0 ml/100 g, 25 ml/100 g, 50 ml/100 g, 75 ml/100 g, and 100 ml/100 g), while the second factor was the dosage of S. cerevisiae isolate MUTJ0F i.e. 5 ml/100 g, and 10 ml/100 g) of the mixed organic waste.” What does the “factor” stands for?

“… until a solution that was supersaturated formed.”

“After the biogas was collected, a measurement cylinder containing the gas was carefully placed.”

“… varied in the amount of composition owing to the variability in the
composition of the samples of the different substrates.”

“Among with significant potential for biogas production (Panahi et al., 2022; Zeng et al., 2022). All the substrates, cafeteria leftover food had the highest organic carbon content (41.6%), …”

“This makes it a high-energy feedstock substrates were considered acceptable for anaerobic digestion because all the mixed wastes had the highest ratio of VS to TS in Table 1.”

“This low pH value was permitted very little methanogenic bacterial activity …”

Avoid stating the mesophilic condition twice in the abstract section.
"physic-chemical properties" = "physicochemical properties"
Use SI units. For example “hrs” = “h”
These sentences should be merged to improve clarity.

“The brine solution was then acidified by adding two to three drops of sulfuric acid by the method of (Elijah et al., 2009). Finally, this formed solution was contained in the second chamber.”
“These values indicated that there were sufficient biodegradable volatile solids in each substrate to enable effective anaerobic digestion (Li et al., 2013; Pagliacci et al., 2016; Kawai et al., 2014). The amount of biodegradable organic matter in the dry matter content should be between 70 and 95% for efficient biogas production (Wu et al., 2021; Buffiere et al., 2006).”

“This increase is due to ammonification processes …” Since this sentence was not verified by measurement, it would be better to express it as “This increase may be due to ammonification processes …”

Is the work clearly and accurately presented and does it cite the current literature?

Partly
Is the study design appropriate and is the work technically sound?

Partly
Are sufficient details of methods and analysis provided to allow replication by others?

Partly
If applicable, is the statistical analysis and its interpretation appropriate?

Not applicable
Are all the source data underlying the results available to ensure full reproducibility?

Partly
Are the conclusions drawn adequately supported by the results?

Partly

Competing Interests: No competing interests were disclosed.

Reviewer Expertise: Anaerobic digestion, pyrolysis and gasification

CITE

Report a concern

Author Response 18 Apr 2026

Mulugeta Fentahun, College of Natural and Computational Sciences, Department of Biology, Debre Markos University, Debre Markos, 269, Ethiopia

18 Apr 2026

Author Response
Mulugeta Fentahun
Thanks to Dr. Dominic Yellezuome for your constructive comments. We conducted a number of changes.
I greatly appreciate your feedback and suggestions. Please find my responses to ... Continue reading
Mulugeta Fentahun
Thanks to Dr. Dominic Yellezuome for your constructive comments. We conducted a number of changes.
I greatly appreciate your feedback and suggestions. Please find my responses to your comments below:

Comment 1: There is too much information in the methods paragraph in the Abstract Section, in which some of it can not be found in the Methods Section. Some of them are not important to be in the Abstract Section.

Response: Thank you for this helpful comment. We have revised the abstract according to your feedback. Refer to the abstract part in the updated manuscript

Comment 2: These sentences are similar; hence should be merged.

Response: Thank you for this observation. We have revised the manuscript by merging similar sentences to improve readability and eliminate redundancy (Refer to the revised manuscript).

Comment 3: Authors cited lists of 3 or more references without proper justification of the relevance of each one. Hence, avoid citing more than two references and outdated references (Refer to the revised manuscript).

Response: Thank you for this constructive comment. We have revised the manuscript by limiting citations and avoiding outdated references (Refer to the revised manuscript).

Comment 4: Although there is information on biogas production from organic waste or single inoculums (Alemayehu, 2014; Abayneh et al., 2014; Hammad et al., 2018; Earnest and Singh, 2013) but there is limited reports on methods for increasing biogas generation, particularly those that use rumen fluid and S. cerevisiae.” This paper is not clear in the description of the scientific novelty in comparison to related previously published and referenced in your work below:

Response: Thank you for this important comment. We have revised the manuscript based on your comments (Refer to the revised manuscript).

Comment 5: There are 107,684 residents, comprising 49,893 men and 57,791 women (Aynalem et al., 2014).” These statistics are outdated.

Response: Thank you for pointing this out. We have updated the demographic information using the most recent and reliable data sources to ensure accuracy and relevance in the manuscript.

Comment 6: This study aimed to evaluate the effects of ruminant fluids and S. cerevisiae isolate MUTJ0F (OR209280.1) on biogas generation from various mixed organic wastes co-digested with cattle manure. Various wastes from fruits and vegetables were gathered from the town fruit houses, leftover food from the Debre Markos University student cafeteria, fresh cattle manure (CM) from Monkorer Agroindustry Enterprise, and rumen fluids (RL) from a nearby slaughterhouse and used as activators for biogas production.” These sentences contains repititions in the next paragraph, hence should be avoided.

Response: Thank you for this comment. We have revised the manuscript to remove the repetitive sentences.

Comment 7: The de-sized cattle manure and food waste were mixed separately with distilled water in a 1:5 (solid waste: distilled water) volume ratio …” What is the ratio between cafeteria leftovers, cattle manure, and fruit and vegetable waste? How was the solid waste measured in volume?.

Response: Thank you for this insightful comment. We have revised the manuscript to clarify the mixing ratios and measurement procedures (Refer to the revised manuscript).

Comment 8: What is the size of the filter used in filtering the rumen fluid?

Response: Thank you for this comment. We have revised the manuscript based on your comments (Refer to the revised manuscript).

Comment 9: Some of the citations are not necessary, such as ○ “Then, different amounts of the filtrate were added to each digester to initiate the reaction (Aurora, 1983; Genet et al., 2018).” “After calibration, the electrode was submerged in the substrate samples, rinsed with distilled water, and the pH values were recorded (Arogo et al., 2009).

Response: Thank you for this comment. We have revised the manuscript by removing unnecessary citations.

Comment 10: In subsection 2.5.1, how was the measured empty crucible used in the formula?

Response: Thank you for this comment. We have revised and clarified the method in subsection 2.5.1 based on your feedback (Refer to the updated manuscript).

Comment 11: In subsection 2.5.2, the authors indicated the measurement of fixed solids, but it was not presented in Table 1.

Response: Thank you for this comment. We have revised the manuscript by include the measured fixed solids in Table 1 or clarified in the manuscript.

Comment 12: Authors should be consistent with the way they explain parameters in an equation, whether horizontal or vertical.

Response: Thank you for this comment. We have revised the manuscript to present all equation parameters consistently in a horizontal format (Refer to the updated manuscript).

Comment 13: The procedure for moisture content determination is the same as that of total solids, so you can indicate the formula of MC there and delete subsection 2.5.4.

Response: Thank you for this suggestion. We have removed subsection 2.5.4 and included the formula for moisture content within the total solids section, streamlining the methods and avoiding redundancy.

Comment 14: After calibration, the electrode was submerged in the substrate samples, rinsed with distilled water, and the pH values were recorded (Arogo et al., 2009).” Are the authors sure this was the sequence used in measuring the pH value?

Response: Thank you for this comment. We have revised the correct sequence and refer to the updated the manuscript.

Comment 15: The first factor was the dosage of rumen liquid i.e. 0 ml/100 g, 25 ml/100 g, 50 ml/100 g, 75 ml/100 g, and 100 ml/100 g), …” Why is the 150 ml rumen fluid not stated here but in Table 2?

Response: Thank you for this comment. We have revised the manuscript to include the 150 ml/100 g rumen fluid level in the text for consistency with Table 2.

Comment 16: The study was conducted at room temperature (30°C).” How did the authors maintain this temperature in the room?

Response: Thank you for this comment. We have clarified in the manuscript that the study was conducted under mesophilic conditions at 38 °C using an oven, and the text has been corrected to fix the typographical error.

Comment 17: Feed stock was mixed with distilled water to obtain approximately 8% of TS suspension.” Is this information similar to the “1:5 (solid waste: distilled water) volume ratio” indicated in section 2.3?

Response: Thank you for this comment. We have clarified in the manuscript that the 8% TS suspension is distinct from the 1:5 ratio described in section 2.3.

Comment 18: In section 2.6, the retention time or duration of the anaerobic digestion was not mentioned.

Response: Thank you for this comment. We have revised section 2.7 based on your comment.

Comment 19: Section 2.7 should come before Section 2.6. Also, the authors need to provide an image of the three plastic bottles set up for anaerobic digestion, since it was constructed for this study. What is the working volume of the digester?

Response: Thank you for this comment. We have revised the manuscript and we have added an image of the three plastic bottle digesters used in this study and the working volume of digester.

Comment 20: Sections 2.8 and 2.7 can be merged. Was the biogas measured daily or at what interval?

Response: Thank you for this comment. We have merged sections 2.7 and 2.8 for clarity and streamlined the methods. We also clarified that biogas production was measured at regular daily intervals throughout the experiment.

Comment 21: In section 3.1, what does the use of “mixed wastes” mean? For example: “The pH of the mixed waste ranged from 6.8 to 7.6, …” Does it mean the mixture of the various feedstock or the individual feedstock?

Response: Thank you for this comment. We have clarified in section 3.1 based on your comments. Refer to the results and discussion parts in the updated manuscript.

Comment 22: The VS/TS ratios of the cafeteria food waste and cattle manure were 78.3% and 91.2%, respectively.” What about fruit and vegetable waste?

Response: Thank you for this comment. We have revised the manuscript based on your comments.

Comment 23: Cattle dung is used to accelerate biogas production by promoting bacterial growth in the digester.” Provide a reference.

Response: Thank you for this comment. We have added a relevant reference. Refer to the updated manuscript.

Comment 24: Co-digestion has a positive synergistic effect by neutralizing pH, increasing buffering capacity, reducing the effects of harmful compounds, and supplying more balanced nutrients, such as vitamins, trace metals, and other substances required for microbial growth (Fang, 2010; Aragaw et al., 2013; Jianzheng et al., 2011).” The relevance of this information in the Results and Discussion Section is not clear since it has already been stated in the Introduction Section with different references cited.

Response: Thank you for this comment. We have revised the results and discussion section and remove the redundant statement.

Comment 25: The 12 methane production treatments varied significantly, reflecting variations in the mixed waste composition and inoculum dosage.” Are the authors sure that the variations in the mixed-waste composition may have caused the significant difference in biogas production?

Response: Thank you for this comment. We have revised the manuscript based on your comments.

Comment 26: This implies that the high anaerobic bacterial concentration in rumen fluid efficiently breaks down organic substrates from mixed waste.” Is it only the rumen fluid that increased biogas production?

Response: Thank you for this comment. We have revised the manuscript based on your comments.

Comment 27: According to the results, the maximum amount of biogas (6900.3 ml) …” Normally, biogas production is evaluated using methane yield (mL/gVS or mL/gTS) to enable comparison with other published studies.

Response: Thank you for this comment. We clarify that our results were reported based on the total biogas volume (mL), and we did not measure total solids or volatile solids after digestion (methane yield (mL/gVS or mL/gTS) in this experiment.

Comment 28: In Table 2, why was only rumen fluid not investigated? The heading “Methane (mean ± SD)”, did the authors measure methane or biogas?

Response: Thank you for this comment. We have clarified that Table 2 presents biogas production and not methane specifically; the heading has been corrected accordingly. Additionally, rumen fluid alone was not included as a treatment because the study focused on co-digestion with mixed wastes to evaluate the synergistic effect of dual inoculants.

Comment 29: In Figure 1, please plot pH on the y-axis and days on the x-axis. Why plot only T10? It is better to plot all the treatments. Why was the pH measured up to 80 days, but the anaerobic digestion was observed for 60 days, as indicated in Figure 2, the Abstract and Section 3.4?

Response: Thank you for this comment. We have revised Figure 1 to plot pH on the y-axis against days on the x-axis and included all treatments for clarity. Additionally, we clarified that pH measurements were continued up to 80 days to monitor post-digestion stabilization, even though the main anaerobic digestion period lasted 60 days.

Comment 30: Figure 2A and B should come before Figure 1.

Response: Thank you for this comment. We have revised the manuscript so that Figures 2A and 2B now appear before Figure 1.

Comment 31: These sentences could have been verified by plotting the daily biogas production.

Response: Thank you for this comment. We have revised the sentences in the updated manuscript.

Comment 32: The authors should clarify which equipment was used for the combustion test, either “a lit matchstick” as indicated in Section 2.9 or “a Bunsen burner” as indicated in Section 3.4. Also, Figure 2C was not well captured to help identify which equipment was used. In section 3.4, it is better use “Figure 2C” rather than “Figure 2”

Response: Thank you for this comment. We have revised the manuscript in the method section and the results and discussion sections.

Comment 33: Biodegradation, microbial strength, and biogas generation can all be enhanced by using” How were biodegradation and microbial strength measured in this study

Response: Thank you for this comment. We have revised the manuscript based on your comments.

Comment 34: Future perspectives or studies could be added to the Conclusion section.

Response: Thank you for this comment. We have revised the conclusion section to include future perspectives.

Comment 35: The language must be checked thoroughly.

Response: Thank you for this comment. We have carefully reviewed and revised the manuscript to improve language, grammar, and clarity throughout the text.

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors
Mulugeta Fentahun
Thanks to Dr. Dominic Yellezuome for your constructive comments. We conducted a number of changes.
I greatly appreciate your feedback and suggestions. Please find my responses to your comments below:

Comment 1: There is too much information in the methods paragraph in the Abstract Section, in which some of it can not be found in the Methods Section. Some of them are not important to be in the Abstract Section.

Response: Thank you for this helpful comment. We have revised the abstract according to your feedback. Refer to the abstract part in the updated manuscript

Comment 2: These sentences are similar; hence should be merged.

Response: Thank you for this observation. We have revised the manuscript by merging similar sentences to improve readability and eliminate redundancy (Refer to the revised manuscript).

Comment 3: Authors cited lists of 3 or more references without proper justification of the relevance of each one. Hence, avoid citing more than two references and outdated references (Refer to the revised manuscript).

Response: Thank you for this constructive comment. We have revised the manuscript by limiting citations and avoiding outdated references (Refer to the revised manuscript).

Comment 4: Although there is information on biogas production from organic waste or single inoculums (Alemayehu, 2014; Abayneh et al., 2014; Hammad et al., 2018; Earnest and Singh, 2013) but there is limited reports on methods for increasing biogas generation, particularly those that use rumen fluid and S. cerevisiae.” This paper is not clear in the description of the scientific novelty in comparison to related previously published and referenced in your work below:

Response: Thank you for this important comment. We have revised the manuscript based on your comments (Refer to the revised manuscript).

Comment 5: There are 107,684 residents, comprising 49,893 men and 57,791 women (Aynalem et al., 2014).” These statistics are outdated.

Response: Thank you for pointing this out. We have updated the demographic information using the most recent and reliable data sources to ensure accuracy and relevance in the manuscript.

Comment 6: This study aimed to evaluate the effects of ruminant fluids and S. cerevisiae isolate MUTJ0F (OR209280.1) on biogas generation from various mixed organic wastes co-digested with cattle manure. Various wastes from fruits and vegetables were gathered from the town fruit houses, leftover food from the Debre Markos University student cafeteria, fresh cattle manure (CM) from Monkorer Agroindustry Enterprise, and rumen fluids (RL) from a nearby slaughterhouse and used as activators for biogas production.” These sentences contains repititions in the next paragraph, hence should be avoided.

Response: Thank you for this comment. We have revised the manuscript to remove the repetitive sentences.

Comment 7: The de-sized cattle manure and food waste were mixed separately with distilled water in a 1:5 (solid waste: distilled water) volume ratio …” What is the ratio between cafeteria leftovers, cattle manure, and fruit and vegetable waste? How was the solid waste measured in volume?.

Response: Thank you for this insightful comment. We have revised the manuscript to clarify the mixing ratios and measurement procedures (Refer to the revised manuscript).

Comment 8: What is the size of the filter used in filtering the rumen fluid?

Response: Thank you for this comment. We have revised the manuscript based on your comments (Refer to the revised manuscript).

Comment 9: Some of the citations are not necessary, such as ○ “Then, different amounts of the filtrate were added to each digester to initiate the reaction (Aurora, 1983; Genet et al., 2018).” “After calibration, the electrode was submerged in the substrate samples, rinsed with distilled water, and the pH values were recorded (Arogo et al., 2009).

Response: Thank you for this comment. We have revised the manuscript by removing unnecessary citations.

Comment 10: In subsection 2.5.1, how was the measured empty crucible used in the formula?

Response: Thank you for this comment. We have revised and clarified the method in subsection 2.5.1 based on your feedback (Refer to the updated manuscript).

Comment 11: In subsection 2.5.2, the authors indicated the measurement of fixed solids, but it was not presented in Table 1.

Response: Thank you for this comment. We have revised the manuscript by include the measured fixed solids in Table 1 or clarified in the manuscript.

Comment 12: Authors should be consistent with the way they explain parameters in an equation, whether horizontal or vertical.

Response: Thank you for this comment. We have revised the manuscript to present all equation parameters consistently in a horizontal format (Refer to the updated manuscript).

Comment 13: The procedure for moisture content determination is the same as that of total solids, so you can indicate the formula of MC there and delete subsection 2.5.4.

Response: Thank you for this suggestion. We have removed subsection 2.5.4 and included the formula for moisture content within the total solids section, streamlining the methods and avoiding redundancy.

Comment 14: After calibration, the electrode was submerged in the substrate samples, rinsed with distilled water, and the pH values were recorded (Arogo et al., 2009).” Are the authors sure this was the sequence used in measuring the pH value?

Response: Thank you for this comment. We have revised the correct sequence and refer to the updated the manuscript.

Comment 15: The first factor was the dosage of rumen liquid i.e. 0 ml/100 g, 25 ml/100 g, 50 ml/100 g, 75 ml/100 g, and 100 ml/100 g), …” Why is the 150 ml rumen fluid not stated here but in Table 2?

Response: Thank you for this comment. We have revised the manuscript to include the 150 ml/100 g rumen fluid level in the text for consistency with Table 2.

Comment 16: The study was conducted at room temperature (30°C).” How did the authors maintain this temperature in the room?

Response: Thank you for this comment. We have clarified in the manuscript that the study was conducted under mesophilic conditions at 38 °C using an oven, and the text has been corrected to fix the typographical error.

Comment 17: Feed stock was mixed with distilled water to obtain approximately 8% of TS suspension.” Is this information similar to the “1:5 (solid waste: distilled water) volume ratio” indicated in section 2.3?

Response: Thank you for this comment. We have clarified in the manuscript that the 8% TS suspension is distinct from the 1:5 ratio described in section 2.3.

Comment 18: In section 2.6, the retention time or duration of the anaerobic digestion was not mentioned.

Response: Thank you for this comment. We have revised section 2.7 based on your comment.

Comment 19: Section 2.7 should come before Section 2.6. Also, the authors need to provide an image of the three plastic bottles set up for anaerobic digestion, since it was constructed for this study. What is the working volume of the digester?

Response: Thank you for this comment. We have revised the manuscript and we have added an image of the three plastic bottle digesters used in this study and the working volume of digester.

Comment 20: Sections 2.8 and 2.7 can be merged. Was the biogas measured daily or at what interval?

Response: Thank you for this comment. We have merged sections 2.7 and 2.8 for clarity and streamlined the methods. We also clarified that biogas production was measured at regular daily intervals throughout the experiment.

Comment 21: In section 3.1, what does the use of “mixed wastes” mean? For example: “The pH of the mixed waste ranged from 6.8 to 7.6, …” Does it mean the mixture of the various feedstock or the individual feedstock?

Response: Thank you for this comment. We have clarified in section 3.1 based on your comments. Refer to the results and discussion parts in the updated manuscript.

Comment 22: The VS/TS ratios of the cafeteria food waste and cattle manure were 78.3% and 91.2%, respectively.” What about fruit and vegetable waste?

Response: Thank you for this comment. We have revised the manuscript based on your comments.

Comment 23: Cattle dung is used to accelerate biogas production by promoting bacterial growth in the digester.” Provide a reference.

Response: Thank you for this comment. We have added a relevant reference. Refer to the updated manuscript.

Comment 24: Co-digestion has a positive synergistic effect by neutralizing pH, increasing buffering capacity, reducing the effects of harmful compounds, and supplying more balanced nutrients, such as vitamins, trace metals, and other substances required for microbial growth (Fang, 2010; Aragaw et al., 2013; Jianzheng et al., 2011).” The relevance of this information in the Results and Discussion Section is not clear since it has already been stated in the Introduction Section with different references cited.

Response: Thank you for this comment. We have revised the results and discussion section and remove the redundant statement.

Comment 25: The 12 methane production treatments varied significantly, reflecting variations in the mixed waste composition and inoculum dosage.” Are the authors sure that the variations in the mixed-waste composition may have caused the significant difference in biogas production?

Response: Thank you for this comment. We have revised the manuscript based on your comments.

Comment 26: This implies that the high anaerobic bacterial concentration in rumen fluid efficiently breaks down organic substrates from mixed waste.” Is it only the rumen fluid that increased biogas production?

Response: Thank you for this comment. We have revised the manuscript based on your comments.

Comment 27: According to the results, the maximum amount of biogas (6900.3 ml) …” Normally, biogas production is evaluated using methane yield (mL/gVS or mL/gTS) to enable comparison with other published studies.

Response: Thank you for this comment. We clarify that our results were reported based on the total biogas volume (mL), and we did not measure total solids or volatile solids after digestion (methane yield (mL/gVS or mL/gTS) in this experiment.

Comment 28: In Table 2, why was only rumen fluid not investigated? The heading “Methane (mean ± SD)”, did the authors measure methane or biogas?

Response: Thank you for this comment. We have clarified that Table 2 presents biogas production and not methane specifically; the heading has been corrected accordingly. Additionally, rumen fluid alone was not included as a treatment because the study focused on co-digestion with mixed wastes to evaluate the synergistic effect of dual inoculants.

Comment 29: In Figure 1, please plot pH on the y-axis and days on the x-axis. Why plot only T10? It is better to plot all the treatments. Why was the pH measured up to 80 days, but the anaerobic digestion was observed for 60 days, as indicated in Figure 2, the Abstract and Section 3.4?

Response: Thank you for this comment. We have revised Figure 1 to plot pH on the y-axis against days on the x-axis and included all treatments for clarity. Additionally, we clarified that pH measurements were continued up to 80 days to monitor post-digestion stabilization, even though the main anaerobic digestion period lasted 60 days.

Comment 30: Figure 2A and B should come before Figure 1.

Response: Thank you for this comment. We have revised the manuscript so that Figures 2A and 2B now appear before Figure 1.

Comment 31: These sentences could have been verified by plotting the daily biogas production.

Response: Thank you for this comment. We have revised the sentences in the updated manuscript.

Comment 32: The authors should clarify which equipment was used for the combustion test, either “a lit matchstick” as indicated in Section 2.9 or “a Bunsen burner” as indicated in Section 3.4. Also, Figure 2C was not well captured to help identify which equipment was used. In section 3.4, it is better use “Figure 2C” rather than “Figure 2”

Response: Thank you for this comment. We have revised the manuscript in the method section and the results and discussion sections.

Comment 33: Biodegradation, microbial strength, and biogas generation can all be enhanced by using” How were biodegradation and microbial strength measured in this study

Response: Thank you for this comment. We have revised the manuscript based on your comments.

Comment 34: Future perspectives or studies could be added to the Conclusion section.

Response: Thank you for this comment. We have revised the conclusion section to include future perspectives.

Comment 35: The language must be checked thoroughly.

Response: Thank you for this comment. We have carefully reviewed and revised the manuscript to improve language, grammar, and clarity throughout the text.

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors
Competing Interests: No competing interests were disclosed. Close
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COMMENTS ON THIS REPORT

Author Response 18 Apr 2026

Mulugeta Fentahun, College of Natural and Computational Sciences, Department of Biology, Debre Markos University, Debre Markos, 269, Ethiopia

18 Apr 2026

Author Response
Mulugeta Fentahun
Thanks to Dr. Dominic Yellezuome for your constructive comments. We conducted a number of changes.
I greatly appreciate your feedback and suggestions. Please find my responses to ... Continue reading
Mulugeta Fentahun
Thanks to Dr. Dominic Yellezuome for your constructive comments. We conducted a number of changes.
I greatly appreciate your feedback and suggestions. Please find my responses to your comments below:

Comment 1: There is too much information in the methods paragraph in the Abstract Section, in which some of it can not be found in the Methods Section. Some of them are not important to be in the Abstract Section.

Response: Thank you for this helpful comment. We have revised the abstract according to your feedback. Refer to the abstract part in the updated manuscript

Comment 2: These sentences are similar; hence should be merged.

Response: Thank you for this observation. We have revised the manuscript by merging similar sentences to improve readability and eliminate redundancy (Refer to the revised manuscript).

Comment 3: Authors cited lists of 3 or more references without proper justification of the relevance of each one. Hence, avoid citing more than two references and outdated references (Refer to the revised manuscript).

Response: Thank you for this constructive comment. We have revised the manuscript by limiting citations and avoiding outdated references (Refer to the revised manuscript).

Comment 4: Although there is information on biogas production from organic waste or single inoculums (Alemayehu, 2014; Abayneh et al., 2014; Hammad et al., 2018; Earnest and Singh, 2013) but there is limited reports on methods for increasing biogas generation, particularly those that use rumen fluid and S. cerevisiae.” This paper is not clear in the description of the scientific novelty in comparison to related previously published and referenced in your work below:

Response: Thank you for this important comment. We have revised the manuscript based on your comments (Refer to the revised manuscript).

Comment 5: There are 107,684 residents, comprising 49,893 men and 57,791 women (Aynalem et al., 2014).” These statistics are outdated.

Response: Thank you for pointing this out. We have updated the demographic information using the most recent and reliable data sources to ensure accuracy and relevance in the manuscript.

Comment 6: This study aimed to evaluate the effects of ruminant fluids and S. cerevisiae isolate MUTJ0F (OR209280.1) on biogas generation from various mixed organic wastes co-digested with cattle manure. Various wastes from fruits and vegetables were gathered from the town fruit houses, leftover food from the Debre Markos University student cafeteria, fresh cattle manure (CM) from Monkorer Agroindustry Enterprise, and rumen fluids (RL) from a nearby slaughterhouse and used as activators for biogas production.” These sentences contains repititions in the next paragraph, hence should be avoided.

Response: Thank you for this comment. We have revised the manuscript to remove the repetitive sentences.

Comment 7: The de-sized cattle manure and food waste were mixed separately with distilled water in a 1:5 (solid waste: distilled water) volume ratio …” What is the ratio between cafeteria leftovers, cattle manure, and fruit and vegetable waste? How was the solid waste measured in volume?.

Response: Thank you for this insightful comment. We have revised the manuscript to clarify the mixing ratios and measurement procedures (Refer to the revised manuscript).

Comment 8: What is the size of the filter used in filtering the rumen fluid?

Response: Thank you for this comment. We have revised the manuscript based on your comments (Refer to the revised manuscript).

Comment 9: Some of the citations are not necessary, such as ○ “Then, different amounts of the filtrate were added to each digester to initiate the reaction (Aurora, 1983; Genet et al., 2018).” “After calibration, the electrode was submerged in the substrate samples, rinsed with distilled water, and the pH values were recorded (Arogo et al., 2009).

Response: Thank you for this comment. We have revised the manuscript by removing unnecessary citations.

Comment 10: In subsection 2.5.1, how was the measured empty crucible used in the formula?

Response: Thank you for this comment. We have revised and clarified the method in subsection 2.5.1 based on your feedback (Refer to the updated manuscript).

Comment 11: In subsection 2.5.2, the authors indicated the measurement of fixed solids, but it was not presented in Table 1.

Response: Thank you for this comment. We have revised the manuscript by include the measured fixed solids in Table 1 or clarified in the manuscript.

Comment 12: Authors should be consistent with the way they explain parameters in an equation, whether horizontal or vertical.

Response: Thank you for this comment. We have revised the manuscript to present all equation parameters consistently in a horizontal format (Refer to the updated manuscript).

Comment 13: The procedure for moisture content determination is the same as that of total solids, so you can indicate the formula of MC there and delete subsection 2.5.4.

Response: Thank you for this suggestion. We have removed subsection 2.5.4 and included the formula for moisture content within the total solids section, streamlining the methods and avoiding redundancy.

Comment 14: After calibration, the electrode was submerged in the substrate samples, rinsed with distilled water, and the pH values were recorded (Arogo et al., 2009).” Are the authors sure this was the sequence used in measuring the pH value?

Response: Thank you for this comment. We have revised the correct sequence and refer to the updated the manuscript.

Comment 15: The first factor was the dosage of rumen liquid i.e. 0 ml/100 g, 25 ml/100 g, 50 ml/100 g, 75 ml/100 g, and 100 ml/100 g), …” Why is the 150 ml rumen fluid not stated here but in Table 2?

Response: Thank you for this comment. We have revised the manuscript to include the 150 ml/100 g rumen fluid level in the text for consistency with Table 2.

Comment 16: The study was conducted at room temperature (30°C).” How did the authors maintain this temperature in the room?

Response: Thank you for this comment. We have clarified in the manuscript that the study was conducted under mesophilic conditions at 38 °C using an oven, and the text has been corrected to fix the typographical error.

Comment 17: Feed stock was mixed with distilled water to obtain approximately 8% of TS suspension.” Is this information similar to the “1:5 (solid waste: distilled water) volume ratio” indicated in section 2.3?

Response: Thank you for this comment. We have clarified in the manuscript that the 8% TS suspension is distinct from the 1:5 ratio described in section 2.3.

Comment 18: In section 2.6, the retention time or duration of the anaerobic digestion was not mentioned.

Response: Thank you for this comment. We have revised section 2.7 based on your comment.

Comment 19: Section 2.7 should come before Section 2.6. Also, the authors need to provide an image of the three plastic bottles set up for anaerobic digestion, since it was constructed for this study. What is the working volume of the digester?

Response: Thank you for this comment. We have revised the manuscript and we have added an image of the three plastic bottle digesters used in this study and the working volume of digester.

Comment 20: Sections 2.8 and 2.7 can be merged. Was the biogas measured daily or at what interval?

Response: Thank you for this comment. We have merged sections 2.7 and 2.8 for clarity and streamlined the methods. We also clarified that biogas production was measured at regular daily intervals throughout the experiment.

Comment 21: In section 3.1, what does the use of “mixed wastes” mean? For example: “The pH of the mixed waste ranged from 6.8 to 7.6, …” Does it mean the mixture of the various feedstock or the individual feedstock?

Response: Thank you for this comment. We have clarified in section 3.1 based on your comments. Refer to the results and discussion parts in the updated manuscript.

Comment 22: The VS/TS ratios of the cafeteria food waste and cattle manure were 78.3% and 91.2%, respectively.” What about fruit and vegetable waste?

Response: Thank you for this comment. We have revised the manuscript based on your comments.

Comment 23: Cattle dung is used to accelerate biogas production by promoting bacterial growth in the digester.” Provide a reference.

Response: Thank you for this comment. We have added a relevant reference. Refer to the updated manuscript.

Comment 24: Co-digestion has a positive synergistic effect by neutralizing pH, increasing buffering capacity, reducing the effects of harmful compounds, and supplying more balanced nutrients, such as vitamins, trace metals, and other substances required for microbial growth (Fang, 2010; Aragaw et al., 2013; Jianzheng et al., 2011).” The relevance of this information in the Results and Discussion Section is not clear since it has already been stated in the Introduction Section with different references cited.

Response: Thank you for this comment. We have revised the results and discussion section and remove the redundant statement.

Comment 25: The 12 methane production treatments varied significantly, reflecting variations in the mixed waste composition and inoculum dosage.” Are the authors sure that the variations in the mixed-waste composition may have caused the significant difference in biogas production?

Response: Thank you for this comment. We have revised the manuscript based on your comments.

Comment 26: This implies that the high anaerobic bacterial concentration in rumen fluid efficiently breaks down organic substrates from mixed waste.” Is it only the rumen fluid that increased biogas production?

Response: Thank you for this comment. We have revised the manuscript based on your comments.

Comment 27: According to the results, the maximum amount of biogas (6900.3 ml) …” Normally, biogas production is evaluated using methane yield (mL/gVS or mL/gTS) to enable comparison with other published studies.

Response: Thank you for this comment. We clarify that our results were reported based on the total biogas volume (mL), and we did not measure total solids or volatile solids after digestion (methane yield (mL/gVS or mL/gTS) in this experiment.

Comment 28: In Table 2, why was only rumen fluid not investigated? The heading “Methane (mean ± SD)”, did the authors measure methane or biogas?

Response: Thank you for this comment. We have clarified that Table 2 presents biogas production and not methane specifically; the heading has been corrected accordingly. Additionally, rumen fluid alone was not included as a treatment because the study focused on co-digestion with mixed wastes to evaluate the synergistic effect of dual inoculants.

Comment 29: In Figure 1, please plot pH on the y-axis and days on the x-axis. Why plot only T10? It is better to plot all the treatments. Why was the pH measured up to 80 days, but the anaerobic digestion was observed for 60 days, as indicated in Figure 2, the Abstract and Section 3.4?

Response: Thank you for this comment. We have revised Figure 1 to plot pH on the y-axis against days on the x-axis and included all treatments for clarity. Additionally, we clarified that pH measurements were continued up to 80 days to monitor post-digestion stabilization, even though the main anaerobic digestion period lasted 60 days.

Comment 30: Figure 2A and B should come before Figure 1.

Response: Thank you for this comment. We have revised the manuscript so that Figures 2A and 2B now appear before Figure 1.

Comment 31: These sentences could have been verified by plotting the daily biogas production.

Response: Thank you for this comment. We have revised the sentences in the updated manuscript.

Comment 32: The authors should clarify which equipment was used for the combustion test, either “a lit matchstick” as indicated in Section 2.9 or “a Bunsen burner” as indicated in Section 3.4. Also, Figure 2C was not well captured to help identify which equipment was used. In section 3.4, it is better use “Figure 2C” rather than “Figure 2”

Response: Thank you for this comment. We have revised the manuscript in the method section and the results and discussion sections.

Comment 33: Biodegradation, microbial strength, and biogas generation can all be enhanced by using” How were biodegradation and microbial strength measured in this study

Response: Thank you for this comment. We have revised the manuscript based on your comments.

Comment 34: Future perspectives or studies could be added to the Conclusion section.

Response: Thank you for this comment. We have revised the conclusion section to include future perspectives.

Comment 35: The language must be checked thoroughly.

Response: Thank you for this comment. We have carefully reviewed and revised the manuscript to improve language, grammar, and clarity throughout the text.

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors
Mulugeta Fentahun
Thanks to Dr. Dominic Yellezuome for your constructive comments. We conducted a number of changes.
I greatly appreciate your feedback and suggestions. Please find my responses to your comments below:

Comment 1: There is too much information in the methods paragraph in the Abstract Section, in which some of it can not be found in the Methods Section. Some of them are not important to be in the Abstract Section.

Response: Thank you for this helpful comment. We have revised the abstract according to your feedback. Refer to the abstract part in the updated manuscript

Comment 2: These sentences are similar; hence should be merged.

Response: Thank you for this observation. We have revised the manuscript by merging similar sentences to improve readability and eliminate redundancy (Refer to the revised manuscript).

Comment 3: Authors cited lists of 3 or more references without proper justification of the relevance of each one. Hence, avoid citing more than two references and outdated references (Refer to the revised manuscript).

Response: Thank you for this constructive comment. We have revised the manuscript by limiting citations and avoiding outdated references (Refer to the revised manuscript).

Comment 4: Although there is information on biogas production from organic waste or single inoculums (Alemayehu, 2014; Abayneh et al., 2014; Hammad et al., 2018; Earnest and Singh, 2013) but there is limited reports on methods for increasing biogas generation, particularly those that use rumen fluid and S. cerevisiae.” This paper is not clear in the description of the scientific novelty in comparison to related previously published and referenced in your work below:

Response: Thank you for this important comment. We have revised the manuscript based on your comments (Refer to the revised manuscript).

Comment 5: There are 107,684 residents, comprising 49,893 men and 57,791 women (Aynalem et al., 2014).” These statistics are outdated.

Response: Thank you for pointing this out. We have updated the demographic information using the most recent and reliable data sources to ensure accuracy and relevance in the manuscript.

Comment 6: This study aimed to evaluate the effects of ruminant fluids and S. cerevisiae isolate MUTJ0F (OR209280.1) on biogas generation from various mixed organic wastes co-digested with cattle manure. Various wastes from fruits and vegetables were gathered from the town fruit houses, leftover food from the Debre Markos University student cafeteria, fresh cattle manure (CM) from Monkorer Agroindustry Enterprise, and rumen fluids (RL) from a nearby slaughterhouse and used as activators for biogas production.” These sentences contains repititions in the next paragraph, hence should be avoided.

Response: Thank you for this comment. We have revised the manuscript to remove the repetitive sentences.

Comment 7: The de-sized cattle manure and food waste were mixed separately with distilled water in a 1:5 (solid waste: distilled water) volume ratio …” What is the ratio between cafeteria leftovers, cattle manure, and fruit and vegetable waste? How was the solid waste measured in volume?.

Response: Thank you for this insightful comment. We have revised the manuscript to clarify the mixing ratios and measurement procedures (Refer to the revised manuscript).

Comment 8: What is the size of the filter used in filtering the rumen fluid?

Response: Thank you for this comment. We have revised the manuscript based on your comments (Refer to the revised manuscript).

Comment 9: Some of the citations are not necessary, such as ○ “Then, different amounts of the filtrate were added to each digester to initiate the reaction (Aurora, 1983; Genet et al., 2018).” “After calibration, the electrode was submerged in the substrate samples, rinsed with distilled water, and the pH values were recorded (Arogo et al., 2009).

Response: Thank you for this comment. We have revised the manuscript by removing unnecessary citations.

Comment 10: In subsection 2.5.1, how was the measured empty crucible used in the formula?

Response: Thank you for this comment. We have revised and clarified the method in subsection 2.5.1 based on your feedback (Refer to the updated manuscript).

Comment 11: In subsection 2.5.2, the authors indicated the measurement of fixed solids, but it was not presented in Table 1.

Response: Thank you for this comment. We have revised the manuscript by include the measured fixed solids in Table 1 or clarified in the manuscript.

Comment 12: Authors should be consistent with the way they explain parameters in an equation, whether horizontal or vertical.

Response: Thank you for this comment. We have revised the manuscript to present all equation parameters consistently in a horizontal format (Refer to the updated manuscript).

Comment 13: The procedure for moisture content determination is the same as that of total solids, so you can indicate the formula of MC there and delete subsection 2.5.4.

Response: Thank you for this suggestion. We have removed subsection 2.5.4 and included the formula for moisture content within the total solids section, streamlining the methods and avoiding redundancy.

Comment 14: After calibration, the electrode was submerged in the substrate samples, rinsed with distilled water, and the pH values were recorded (Arogo et al., 2009).” Are the authors sure this was the sequence used in measuring the pH value?

Response: Thank you for this comment. We have revised the correct sequence and refer to the updated the manuscript.

Comment 15: The first factor was the dosage of rumen liquid i.e. 0 ml/100 g, 25 ml/100 g, 50 ml/100 g, 75 ml/100 g, and 100 ml/100 g), …” Why is the 150 ml rumen fluid not stated here but in Table 2?

Response: Thank you for this comment. We have revised the manuscript to include the 150 ml/100 g rumen fluid level in the text for consistency with Table 2.

Comment 16: The study was conducted at room temperature (30°C).” How did the authors maintain this temperature in the room?

Response: Thank you for this comment. We have clarified in the manuscript that the study was conducted under mesophilic conditions at 38 °C using an oven, and the text has been corrected to fix the typographical error.

Comment 17: Feed stock was mixed with distilled water to obtain approximately 8% of TS suspension.” Is this information similar to the “1:5 (solid waste: distilled water) volume ratio” indicated in section 2.3?

Response: Thank you for this comment. We have clarified in the manuscript that the 8% TS suspension is distinct from the 1:5 ratio described in section 2.3.

Comment 18: In section 2.6, the retention time or duration of the anaerobic digestion was not mentioned.

Response: Thank you for this comment. We have revised section 2.7 based on your comment.

Comment 19: Section 2.7 should come before Section 2.6. Also, the authors need to provide an image of the three plastic bottles set up for anaerobic digestion, since it was constructed for this study. What is the working volume of the digester?

Response: Thank you for this comment. We have revised the manuscript and we have added an image of the three plastic bottle digesters used in this study and the working volume of digester.

Comment 20: Sections 2.8 and 2.7 can be merged. Was the biogas measured daily or at what interval?

Response: Thank you for this comment. We have merged sections 2.7 and 2.8 for clarity and streamlined the methods. We also clarified that biogas production was measured at regular daily intervals throughout the experiment.

Comment 21: In section 3.1, what does the use of “mixed wastes” mean? For example: “The pH of the mixed waste ranged from 6.8 to 7.6, …” Does it mean the mixture of the various feedstock or the individual feedstock?

Response: Thank you for this comment. We have clarified in section 3.1 based on your comments. Refer to the results and discussion parts in the updated manuscript.

Comment 22: The VS/TS ratios of the cafeteria food waste and cattle manure were 78.3% and 91.2%, respectively.” What about fruit and vegetable waste?

Response: Thank you for this comment. We have revised the manuscript based on your comments.

Comment 23: Cattle dung is used to accelerate biogas production by promoting bacterial growth in the digester.” Provide a reference.

Response: Thank you for this comment. We have added a relevant reference. Refer to the updated manuscript.

Comment 24: Co-digestion has a positive synergistic effect by neutralizing pH, increasing buffering capacity, reducing the effects of harmful compounds, and supplying more balanced nutrients, such as vitamins, trace metals, and other substances required for microbial growth (Fang, 2010; Aragaw et al., 2013; Jianzheng et al., 2011).” The relevance of this information in the Results and Discussion Section is not clear since it has already been stated in the Introduction Section with different references cited.

Response: Thank you for this comment. We have revised the results and discussion section and remove the redundant statement.

Comment 25: The 12 methane production treatments varied significantly, reflecting variations in the mixed waste composition and inoculum dosage.” Are the authors sure that the variations in the mixed-waste composition may have caused the significant difference in biogas production?

Response: Thank you for this comment. We have revised the manuscript based on your comments.

Comment 26: This implies that the high anaerobic bacterial concentration in rumen fluid efficiently breaks down organic substrates from mixed waste.” Is it only the rumen fluid that increased biogas production?

Response: Thank you for this comment. We have revised the manuscript based on your comments.

Comment 27: According to the results, the maximum amount of biogas (6900.3 ml) …” Normally, biogas production is evaluated using methane yield (mL/gVS or mL/gTS) to enable comparison with other published studies.

Response: Thank you for this comment. We clarify that our results were reported based on the total biogas volume (mL), and we did not measure total solids or volatile solids after digestion (methane yield (mL/gVS or mL/gTS) in this experiment.

Comment 28: In Table 2, why was only rumen fluid not investigated? The heading “Methane (mean ± SD)”, did the authors measure methane or biogas?

Response: Thank you for this comment. We have clarified that Table 2 presents biogas production and not methane specifically; the heading has been corrected accordingly. Additionally, rumen fluid alone was not included as a treatment because the study focused on co-digestion with mixed wastes to evaluate the synergistic effect of dual inoculants.

Comment 29: In Figure 1, please plot pH on the y-axis and days on the x-axis. Why plot only T10? It is better to plot all the treatments. Why was the pH measured up to 80 days, but the anaerobic digestion was observed for 60 days, as indicated in Figure 2, the Abstract and Section 3.4?

Response: Thank you for this comment. We have revised Figure 1 to plot pH on the y-axis against days on the x-axis and included all treatments for clarity. Additionally, we clarified that pH measurements were continued up to 80 days to monitor post-digestion stabilization, even though the main anaerobic digestion period lasted 60 days.

Comment 30: Figure 2A and B should come before Figure 1.

Response: Thank you for this comment. We have revised the manuscript so that Figures 2A and 2B now appear before Figure 1.

Comment 31: These sentences could have been verified by plotting the daily biogas production.

Response: Thank you for this comment. We have revised the sentences in the updated manuscript.

Comment 32: The authors should clarify which equipment was used for the combustion test, either “a lit matchstick” as indicated in Section 2.9 or “a Bunsen burner” as indicated in Section 3.4. Also, Figure 2C was not well captured to help identify which equipment was used. In section 3.4, it is better use “Figure 2C” rather than “Figure 2”

Response: Thank you for this comment. We have revised the manuscript in the method section and the results and discussion sections.

Comment 33: Biodegradation, microbial strength, and biogas generation can all be enhanced by using” How were biodegradation and microbial strength measured in this study

Response: Thank you for this comment. We have revised the manuscript based on your comments.

Comment 34: Future perspectives or studies could be added to the Conclusion section.

Response: Thank you for this comment. We have revised the conclusion section to include future perspectives.

Comment 35: The language must be checked thoroughly.

Response: Thank you for this comment. We have carefully reviewed and revised the manuscript to improve language, grammar, and clarity throughout the text.

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors
Competing Interests: No competing interests were disclosed. Close
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Version 1

VERSION 1

PUBLISHED 13 Feb 2025

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Reviewer Report 19 Aug 2025

Jovine Kamuhabwa Emmanuel, Chemistry, University of Dar es Salaam, Dar es Salaam, Dar es Salaam, Tanzania

Not Approved

https://doi.org/10.5256/f1000research.177603.r401840

Title

The title captures the content of the current work.

Abstract

The abstract has no information on the study, methodology used and key findings ... Continue reading

Title

The title captures the content of the current work.

Abstract

The abstract has no information on the study, methodology used and key findings and recommendation based on findings. Authors must re-write this to reflect the current work. Other comments are found in the main document.

Introduction

The section has not been written properly and not easy to follow and understand. Authors must write this in a scholarly manner to reflect an article for publication. The novelty is not well feature thus, authors must reveal the novelty of the work. Other comments are found in the main document.

Materials and methods

Proper details and step after step must be provided for readers to follow. Authors need to take time and re-do it properly. Other comments are found in the main document.

Results and discussion

Results are not well organized and discussed with previous work. Authors need to re-think on how they can organize these data for publication. Other comments are found in the main document.

Conclusions and recommendations

This section is not well written thus, must be re-written for clarity. Only key findings and recommendation must be presented and not otherwise. Other comments are found in the main document.

General comment

The manuscript must benefit from a serious English Language editing before being indexed.
The manuscript must be enriched with up-to-date citations which are available in the literature. Other comments are found in the main document.

Is the work clearly and accurately presented and does it cite the current literature?

No
Is the study design appropriate and is the work technically sound?

Yes
Are sufficient details of methods and analysis provided to allow replication by others?

Partly
If applicable, is the statistical analysis and its interpretation appropriate?

Not applicable
Are all the source data underlying the results available to ensure full reproducibility?

Partly
Are the conclusions drawn adequately supported by the results?

Partly

Competing Interests: No competing interests were disclosed.

Reviewer Expertise: Catalysis, materials science and bioenergy

CITE

Report a concern

Author Response 29 Dec 2025

Mulugeta Fentahun, College of Natural and Computational Sciences, Department of Biology, Debre Markos University, Debre Markos, 269, Ethiopia

29 Dec 2025

Author Response
Mulugeta Fentahun
Dr. Jovine Kamuhabwa Emmanuel thank you very much for your insightful comments and the time you dedicated to review.
We greatly appreciate your feedback and suggestions. We ... Continue reading
Mulugeta Fentahun
Dr. Jovine Kamuhabwa Emmanuel thank you very much for your insightful comments and the time you dedicated to review.
We greatly appreciate your feedback and suggestions. We provide a detailed response to each comment, along with the corresponding changes made in the revised manuscript below:

Title:

Comment: The title captures the content of the current work.

Response: Thank you for your positive feedback.

Abstract Revision:

Comment: The abstract has no information on the study, methodology used, and key findings and recommendations based on the findings. Authors must re-write this to reflect the current work.

Response: Thank you for your insightful comment. We have thoroughly revised the abstract part in response to your suggestions (see the revised manuscript).

Introduction Revision:

Comment: The section has not been written properly and is not easy to follow and understand. Authors must write this in a scholarly manner to reflect an article for publication. The novelty is not well featured; thus, authors must reveal the novelty of the work.

Response: We sincerely thank the reviewer for your constructive feedback. We have thoroughly revised the introduction section to improve clarity, coherence, and scholarly manner. Additionally, we have clearly highlighted the novelty of the study by emphasizing its unique contributions in the revised manuscript (refer to the revised manuscript).

Methodology Revision:

Comment: Proper details and step after step must be provided for readers to follow. Authors need to take time and re-do it properly.

Response: Thank you for this valuable observation. We have substantially revised the materials and methods section to improve clarity, completeness, and reproducibility. The updated version now provides detailed, step-by-step procedures for the experimental work, enabling readers to follow the methodology accurately and enhancing the scientific rigor of the manuscript (see the revised manuscript).

Results and Discussion Revision:

Comment: Results are not well organized and discussed with previous work. Authors need to re-think on how they can organize these data for publication.

Response: We sincerely thank the reviewer for your constructive feedback. We have carefully revised the results and discussion section to enhance clarity and coherence. The revised version enriched with up-to-date citations (recent literature) and emphasizes the key findings. Please refer to the updated section in the revised manuscript.

Conclusions and recommendations Revision:

Comment: This section is not well written thus, must be re-written for clarity. Only key findings and recommendation must be presented and not otherwise.

Response: Thank you for your insightful comment. We have revised the conclusions section to clearly highlight the study’s key findings and recommendation. Please see the updated section in the revised manuscript.

General comment:

Comment: The manuscript must benefit from a serious English Language editing before being indexed.

Response: We sincerely thank the reviewer for the valuable suggestion regarding the language quality of our manuscript. We have thoroughly revised the manuscript to improve English clarity, grammar, and readability.

Comment: The manuscript must be enriched with up-to-date citations which are available in the literature.

Response: Thank you for your comments. We have updated the manuscript by incorporating recent literature, as suggested (see the revised manuscript).

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors
Mulugeta Fentahun
Dr. Jovine Kamuhabwa Emmanuel thank you very much for your insightful comments and the time you dedicated to review.
We greatly appreciate your feedback and suggestions. We provide a detailed response to each comment, along with the corresponding changes made in the revised manuscript below:

Title:

Comment: The title captures the content of the current work.

Response: Thank you for your positive feedback.

Abstract Revision:

Comment: The abstract has no information on the study, methodology used, and key findings and recommendations based on the findings. Authors must re-write this to reflect the current work.

Response: Thank you for your insightful comment. We have thoroughly revised the abstract part in response to your suggestions (see the revised manuscript).

Introduction Revision:

Comment: The section has not been written properly and is not easy to follow and understand. Authors must write this in a scholarly manner to reflect an article for publication. The novelty is not well featured; thus, authors must reveal the novelty of the work.

Response: We sincerely thank the reviewer for your constructive feedback. We have thoroughly revised the introduction section to improve clarity, coherence, and scholarly manner. Additionally, we have clearly highlighted the novelty of the study by emphasizing its unique contributions in the revised manuscript (refer to the revised manuscript).

Methodology Revision:

Comment: Proper details and step after step must be provided for readers to follow. Authors need to take time and re-do it properly.

Response: Thank you for this valuable observation. We have substantially revised the materials and methods section to improve clarity, completeness, and reproducibility. The updated version now provides detailed, step-by-step procedures for the experimental work, enabling readers to follow the methodology accurately and enhancing the scientific rigor of the manuscript (see the revised manuscript).

Results and Discussion Revision:

Comment: Results are not well organized and discussed with previous work. Authors need to re-think on how they can organize these data for publication.

Response: We sincerely thank the reviewer for your constructive feedback. We have carefully revised the results and discussion section to enhance clarity and coherence. The revised version enriched with up-to-date citations (recent literature) and emphasizes the key findings. Please refer to the updated section in the revised manuscript.

Conclusions and recommendations Revision:

Comment: This section is not well written thus, must be re-written for clarity. Only key findings and recommendation must be presented and not otherwise.

Response: Thank you for your insightful comment. We have revised the conclusions section to clearly highlight the study’s key findings and recommendation. Please see the updated section in the revised manuscript.

General comment:

Comment: The manuscript must benefit from a serious English Language editing before being indexed.

Response: We sincerely thank the reviewer for the valuable suggestion regarding the language quality of our manuscript. We have thoroughly revised the manuscript to improve English clarity, grammar, and readability.

Comment: The manuscript must be enriched with up-to-date citations which are available in the literature.

Response: Thank you for your comments. We have updated the manuscript by incorporating recent literature, as suggested (see the revised manuscript).

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors
Competing Interests: No competing interests were disclosed. Close
Report a concern
Respond or Comment

COMMENTS ON THIS REPORT

Author Response 29 Dec 2025

Mulugeta Fentahun, College of Natural and Computational Sciences, Department of Biology, Debre Markos University, Debre Markos, 269, Ethiopia

29 Dec 2025

Author Response
Mulugeta Fentahun
Dr. Jovine Kamuhabwa Emmanuel thank you very much for your insightful comments and the time you dedicated to review.
We greatly appreciate your feedback and suggestions. We ... Continue reading
Mulugeta Fentahun
Dr. Jovine Kamuhabwa Emmanuel thank you very much for your insightful comments and the time you dedicated to review.
We greatly appreciate your feedback and suggestions. We provide a detailed response to each comment, along with the corresponding changes made in the revised manuscript below:

Title:

Comment: The title captures the content of the current work.

Response: Thank you for your positive feedback.

Abstract Revision:

Comment: The abstract has no information on the study, methodology used, and key findings and recommendations based on the findings. Authors must re-write this to reflect the current work.

Response: Thank you for your insightful comment. We have thoroughly revised the abstract part in response to your suggestions (see the revised manuscript).

Introduction Revision:

Comment: The section has not been written properly and is not easy to follow and understand. Authors must write this in a scholarly manner to reflect an article for publication. The novelty is not well featured; thus, authors must reveal the novelty of the work.

Response: We sincerely thank the reviewer for your constructive feedback. We have thoroughly revised the introduction section to improve clarity, coherence, and scholarly manner. Additionally, we have clearly highlighted the novelty of the study by emphasizing its unique contributions in the revised manuscript (refer to the revised manuscript).

Methodology Revision:

Comment: Proper details and step after step must be provided for readers to follow. Authors need to take time and re-do it properly.

Response: Thank you for this valuable observation. We have substantially revised the materials and methods section to improve clarity, completeness, and reproducibility. The updated version now provides detailed, step-by-step procedures for the experimental work, enabling readers to follow the methodology accurately and enhancing the scientific rigor of the manuscript (see the revised manuscript).

Results and Discussion Revision:

Comment: Results are not well organized and discussed with previous work. Authors need to re-think on how they can organize these data for publication.

Response: We sincerely thank the reviewer for your constructive feedback. We have carefully revised the results and discussion section to enhance clarity and coherence. The revised version enriched with up-to-date citations (recent literature) and emphasizes the key findings. Please refer to the updated section in the revised manuscript.

Conclusions and recommendations Revision:

Comment: This section is not well written thus, must be re-written for clarity. Only key findings and recommendation must be presented and not otherwise.

Response: Thank you for your insightful comment. We have revised the conclusions section to clearly highlight the study’s key findings and recommendation. Please see the updated section in the revised manuscript.

General comment:

Comment: The manuscript must benefit from a serious English Language editing before being indexed.

Response: We sincerely thank the reviewer for the valuable suggestion regarding the language quality of our manuscript. We have thoroughly revised the manuscript to improve English clarity, grammar, and readability.

Comment: The manuscript must be enriched with up-to-date citations which are available in the literature.

Response: Thank you for your comments. We have updated the manuscript by incorporating recent literature, as suggested (see the revised manuscript).

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors
Mulugeta Fentahun
Dr. Jovine Kamuhabwa Emmanuel thank you very much for your insightful comments and the time you dedicated to review.
We greatly appreciate your feedback and suggestions. We provide a detailed response to each comment, along with the corresponding changes made in the revised manuscript below:

Title:

Comment: The title captures the content of the current work.

Response: Thank you for your positive feedback.

Abstract Revision:

Comment: The abstract has no information on the study, methodology used, and key findings and recommendations based on the findings. Authors must re-write this to reflect the current work.

Response: Thank you for your insightful comment. We have thoroughly revised the abstract part in response to your suggestions (see the revised manuscript).

Introduction Revision:

Comment: The section has not been written properly and is not easy to follow and understand. Authors must write this in a scholarly manner to reflect an article for publication. The novelty is not well featured; thus, authors must reveal the novelty of the work.

Response: We sincerely thank the reviewer for your constructive feedback. We have thoroughly revised the introduction section to improve clarity, coherence, and scholarly manner. Additionally, we have clearly highlighted the novelty of the study by emphasizing its unique contributions in the revised manuscript (refer to the revised manuscript).

Methodology Revision:

Comment: Proper details and step after step must be provided for readers to follow. Authors need to take time and re-do it properly.

Response: Thank you for this valuable observation. We have substantially revised the materials and methods section to improve clarity, completeness, and reproducibility. The updated version now provides detailed, step-by-step procedures for the experimental work, enabling readers to follow the methodology accurately and enhancing the scientific rigor of the manuscript (see the revised manuscript).

Results and Discussion Revision:

Comment: Results are not well organized and discussed with previous work. Authors need to re-think on how they can organize these data for publication.

Response: We sincerely thank the reviewer for your constructive feedback. We have carefully revised the results and discussion section to enhance clarity and coherence. The revised version enriched with up-to-date citations (recent literature) and emphasizes the key findings. Please refer to the updated section in the revised manuscript.

Conclusions and recommendations Revision:

Comment: This section is not well written thus, must be re-written for clarity. Only key findings and recommendation must be presented and not otherwise.

Response: Thank you for your insightful comment. We have revised the conclusions section to clearly highlight the study’s key findings and recommendation. Please see the updated section in the revised manuscript.

General comment:

Comment: The manuscript must benefit from a serious English Language editing before being indexed.

Response: We sincerely thank the reviewer for the valuable suggestion regarding the language quality of our manuscript. We have thoroughly revised the manuscript to improve English clarity, grammar, and readability.

Comment: The manuscript must be enriched with up-to-date citations which are available in the literature.

Response: Thank you for your comments. We have updated the manuscript by incorporating recent literature, as suggested (see the revised manuscript).

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors
Competing Interests: No competing interests were disclosed. Close
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Version 4

VERSION 4 PUBLISHED 13 Feb 2025

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Version 3 (revision) 18 Apr 26		read
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Jovine Kamuhabwa Emmanuel, University of Dar es Salaam, Dar es Salaam, Tanzania
Dominic Yellezuome, University of Mines and Technology, Tarkwa, Ghana
Josef Marousek, Technical University of Košice, Košice–Sever, Slovakia

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Reviewer Report

8 Views

29 Apr 2026 | for Version 3

Dominic Yellezuome, University of Mines and Technology, Tarkwa, Western Region, Ghana

8 Views Cite this report Responses(1)

Approved With Reservations

The manuscript requires a thorough revision before it can be considered for acceptance.

The final sentence in the Methods section of the abstract should either be removed or integrated with the preceding sentence for better flow and clarity.
Several statements are supported by multiple references (three or more) without clearly justifying the relevance of each, and some cited works appear outdated. For example, the last sentence of the first paragraph of the Introduction.
The manuscript does not clearly articulate its scientific novelty in comparison to existing studies. This should be strengthened.
A proper reference should be provided for the rainfall and temperature data reported for Debre Markos.
In Subsection 2.5.1, the formula does not clearly indicate how the empty crucible is accounted for. Additionally, the explanation of variables should be formatted horizontally for consistency with the rest of the manuscript.
The authors indicated that subsection 2.5.4 has been deleted; however, this subsection still remains, which describes the same procedure as subsection 2.5.1.
In Section 2.6, “The 12 treatment types used for anaerobic co-digestion were cattle manure, fruit and vegetable waste, and cafeteria leftover food in mixtures of 1:1 ratio.” How do the three substrates have a mixing ratio of 1:1?
How is the information provided in Section 2.3 “After measuring the total solids (TS) of the samples, the de-sized cattle manure and food waste were mixed separately with distilled water in a 1:5 ratio (w/v) to maintain the total solid in the digester between 8 and 15%, which is the optimum value for wet anaerobic digestion (Ituen et al., 2007).” and Section 2.6 “Feed stock was mixed with distilled water to obtain approximately 8% of TS suspension.” different.
Section 2.7 “Anaerobic digesters (plastic bottles) were constructed for bench-scale experiments, in which biogas was produced from the degradation of substrates in a 0.6 L digester with a working volume of 450 mL.” Why use a different unit?
The retention time (duration) of anaerobic digestion is not specified in Section 2.7, despite being mentioned in the authors’ response. This information should be clearly included.
The control test was not described in the methodology section.
Figure 1 should be referenced in Section 2.7. Additionally, the experimental setup shown does not indicate that the digesters were maintained in an oven, which should be clarified. It is also recommended that Section 2.7 be presented before Section 2.6 for better logical flow.
Referencing Figure 1 again in Section 3.2 is unnecessary and can be removed.
Biogas production should be reported in terms of specific yield (e.g., mL/gVS or mL/gTS) to allow comparison with existing literature. The total solids or volatile solids before digestion are used for this assessment.
The response to the comment regarding the exclusion of rumen fluid (Table 2) is insufficient. The rationale for evaluating only the Saccharomyces cerevisiae isolate (MUTJ0F) instead of including rumen fluid should be clearly justified.
In Table 2, how relevant is the column containing MW₀ – MW₁₂?
Although the authors state that pH was monitored for 80 days to assess post-digestion stabilization, this was not included in the study objectives nor discussed in the Results and Discussion section. This inconsistency should be addressed.
What is the difference between Figure 1b and Figure 3a?
Some responses to reviewer comments lack clarity, making it difficult to understand the revisions made (e.g., Comments 31, 32 and 33). These responses should be improved for transparency.

Competing Interests

No competing interests were disclosed.

Reviewer Expertise

Anaerobic digestion, pyrolysis and gasification

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Author Response

09 Jun 2026

Mulugeta Fentahun, College of Natural and Computational Sciences, Department of Biology, Debre Markos University, Debre Markos, 269, Ethiopia

Mulugeta Fentahun
Thanks to Dr. Dominic Yellezuome for your insightful comments and the time you dedicated to review our article.
I greatly appreciate your feedback and suggestions. Please find our responses to your comments below:

Comment 1: The final sentence in the Methods section of the abstract should either be removed or integrated with the preceding sentence for better flow and clarity.
Response: Thank you for this valuable comment. We have revised the final sentence in the methods section of the abstract by integrating it with the preceding sentence to improve the flow, readability, and clarity of the abstract.
Comment 2: Several statements are supported by multiple references (three or more) without clearly justifying the relevance of each, and some cited works appear outdated. For example, the last sentence of the first paragraph of the Introduction.
Response: Thank you for this important observation. We have carefully reviewed the cited references throughout the manuscript. Redundant citations were reduced, and only the most relevant and recent references were retained to better support each statement.
Comment 3: The manuscript does not clearly articulate its scientific novelty in comparison to existing studies. This should be strengthened.
Response: Thank you for this constructive comment. We have strengthened the manuscript by clearly highlighting the scientific novelty and contribution of the study in the Introduction sections.
Comment 4: A proper reference should be provided for the rainfall and temperature data reported for Debre Markos.
Response: Thank you for this helpful comment. We have revised the manuscript to include appropriate references for the rainfall and temperature data reported for Debre Markos. Please refer to the materials and methods section under the study area description.
Comment 5: In Subsection 2.5.1, the formula does not clearly indicate how the empty crucible is accounted for. Additionally, the explanation of variables should be formatted horizontally for consistency with the rest of the manuscript.
Response: Thank you for this valuable comment. We have revised Subsection 2.5.1 to clearly indicate how the empty crucible weight was accounted for in the formula. In addition, the explanations of the variables used in the equation were reformatted horizontally to ensure consistency with the formatting style used throughout the manuscript.
Comment 6: The authors indicated that subsection 2.5.4 has been deleted; however, this subsection still remains, which describes the same procedure as subsection 2.5.1.
Response: Thank you for this important observation. We apologize for the oversight in the previous revision. The moisture content of each sample was determined using the oven-drying method, and the calculation was carried out using the formula provided in Subsection 2.5.4 (Moisture Content Determination).
Comment 7: In Section 2.6, “The 12 treatment types used for anaerobic co-digestion were cattle manure, fruit and vegetable waste, and cafeteria leftover food in mixtures of 1:1 ratio.” How do the three substrates have a mixing ratio of 1:1?
Response: Thank you for this important clarification. The correct mixing ratio for the three substrates is cafeteria leftover food, fruit and vegetable waste, and cattle manure in a 1:1:2 proportion, respectively. Section 2.6 has been revised to accurately reflect the three-substrate ratio.
Comment 8: How is the information provided in Section 2.3 “After measuring the total solids (TS) of the samples, the de-sized cattle manure and food waste were mixed separately with distilled water in a 1:5 ratio (w/v) to maintain the total solid in the digester between 8 and 15%, which is the optimum value for wet anaerobic digestion (Ituen et al., 2007).” and Section 2.6 “Feed stock was mixed with distilled water to obtain approximately 8% of TS suspension.” different.
Response: Thank you for this important observation. We acknowledge the inconsistency between the two sections of the methods. The manuscript has been revised by removing the repeated and overlapping content to ensure clarity and consistency between sections 2.3 and 2.7.
Comment 9: Section 2.7 “Anaerobic digesters (plastic bottles) were constructed for bench-scale experiments, in which biogas was produced from the degradation of substrates in a 0.6 L digester with a working volume of 450 mL.” Why use a different unit?
Response: Thank you for this important observation. The manuscript has been revised to ensure consistency in unit measurement.
Comment 10: The retention time (duration) of anaerobic digestion is not specified in Section 2.7, despite being mentioned in the authors’ response. This information should be clearly included.
Response: Thank you for this important observation. The manuscript has been revised to include the anaerobic digestion retention time in Section 2.6.
Comment 11: The control test was not described in the methodology section.
Response: Thank you for this important observation. The manuscript has been revised to include the control test in the methodology section. Please refer to the 2.7 experimental setup subsection in the methods section.
Comment 12: Figure 1 should be referenced in Section 2.7. Additionally, the experimental setup shown does not indicate that the digesters were maintained in an oven, which should be clarified. It is also recommended that Section 2.7 be presented before Section 2.6 for better logical flow.
Response: Thank you for this important observation. The manuscript has been revised accordingly. Figure 1 is now properly cited in the method section 2.6 Construction of the anaerobic digesters for batch system according to your comment. In addition, the experimental setup has been clarified to indicate that the digesters were maintained under controlled temperature conditions using an oven. Furthermore, the structure of the Methods section has been reorganized, with Section 2.7 now presented before Section 2.6 to improve the logical flow of the experimental description.
Comment 13: Referencing Figure 1 again in Section 3.2 is unnecessary and can be removed.
Response: Thank you for this helpful suggestion. We agree that repeating the reference to Figure 1 in Section 3.2 is unnecessary. The manuscript has been revised accordingly by removing the redundant citation to Figure 1 to avoid repetition.
Comment 14: Biogas production should be reported in terms of specific yield (e.g., mL/gVS or mL/gTS) to allow comparison with existing literature. The total solids or volatile solids before digestion are used for this assessment.
Response: Thank you for this important suggestion. We agree that reporting biogas production in terms of specific yield is essential for meaningful comparison with existing literature. The manuscript has been revised to present biogas production as biogas yield (mL/gVS), using the initial volatile solids (VS) content of the substrates prior to digestion as the basis for calculation. This improves the comparability and scientific rigor of the results. The Discussion section has also been revised accordingly. The comparison of the findings is mainly based on previous studies on enhancing biogas production from the co-digestion of organic wastes using rumen fluid as an inoculum only. However, studies combining both rumen fluid and Saccharomyces cerevisiae are limited in the literature, and therefore such combined inoculum effects were not discussed. The only relevant available study identified is Achmad KT, Gani SA, Sunarto SI, et al. (2011), The use of rumen liquid and Saccharomyces cerevisiae as activators in biogas production from fresh market garbage, Lucrări Ştiințifice, 56.
Comment 15: The response to the comment regarding the exclusion of rumen fluid (Table 2) is insufficient. The rationale for evaluating only the Saccharomyces cerevisiae isolate (MUTJ0F) instead of including rumen fluid should be clearly justified.
Response: Thank you for this important comment. The primary objective of the study was to evaluate the combined synergistic effect of the locally isolated Saccharomyces cerevisiae MUTJ0F strain in enhancing biogas production from mixed organic wastes under different rumen fluid supplementation levels. For this reason, all experimental treatments were designed to include the yeast strain while varying the amount of rumen fluid.
Comment 16: In Table 2, how relevant is the column containing MW0 – MW12?
Response: Thank you for this important comment. The manuscript has been revised by removing the column section from the Table 2 to avoid redundancy and improve clarity.
Comment 17: Although the authors state that pH was monitored for 80 days to assess post-digestion stabilization, this was not included in the study objectives nor discussed in the Results and Discussion section. This inconsistency should be addressed.
Response: Thank you for this important observation. We agree that the pH monitoring over 80 days was not clearly aligned with the stated objectives and was not sufficiently discussed in the Results and Discussion section. The manuscript has now been revised to address this inconsistency in the study objectives, methodology, and discussion section. The discussion has been expanded to explain pH variations in process stability and post-digestion stabilization in the digesters.
Comment 18: What is the difference between Figure 1b and Figure 3a?
Response: Figure 1b illustrates the complete experimental setup, including all functional components arranged for the anaerobic digestion process. In contrast, Figure 3a shows the digester bottles during the combustibility test, representing the practical application stage in which biogas production was evaluated through flame ignition. This figure was included to clearly demonstrate the combustibility of the biogas in a visible and understandable way for readers.
Comment 19: Some responses to reviewer comments lack clarity, making it difficult to understand the revisions made (e.g., Comments 31, 32 and 33). These responses should be improved for transparency.
Response: Thank you for this observation. We have carefully considered and addressed your comments. The revised version of the manuscript clearly describes the specific changes made, including the relevant sections.

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors

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Competing Interests

No competing interests were disclosed.

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Reviewer Report

7 Views

13 Jan 2026 | for Version 2

Josef Marousek, Technical University of Košice, Košice–Sever, Slovakia

7 Views Cite this report Responses(1)

Not Approved

Is the work clearly and accurately presented and does it cite the current literature?

No
Is the study design appropriate and is the work technically sound?

Partly
Are sufficient details of methods and analysis provided to allow replication by others?

Partly
If applicable, is the statistical analysis and its interpretation appropriate?

Partly
Are all the source data underlying the results available to ensure full reproducibility?

No
Are the conclusions drawn adequately supported by the results?

No

Competing Interests

No competing interests were disclosed.

Reviewer Expertise

phytotechnology, commercialization

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Responses (1)

Author Response

18 Apr 2026

Mulugeta Fentahun, College of Natural and Computational Sciences, Department of Biology, Debre Markos University, Debre Markos, 269, Ethiopia

Mulugeta Fentahun
Professor Josef Marousek thank you very much for your insightful comments and the time you dedicated to review our article.
I greatly appreciate your feedback and suggestions. Please find my responses to your comments below:

Comment1: The urgency and significance of the research hypothesis needs to be better justified and placed into [economic/industrial/environmental] context.
Response: Thank you for this valuable comment. We have revised the manuscript to better clarify the urgency and significance of the research hypothesis within economic, industrial, and environmental contexts. Refer to the introduction part of the updated manuscript.
Comment2: It is appropriate to adapt the methodology to the current state of knowledge
Response: Thank you for this helpful comment. We have revised the methodology to align with the current state of knowledge by updating the experimental method based on recent literature. Refer to the method section of the updated manuscript.
Comment3: The applicability needs to be strengthened [cost breakdown and corresponding financial analyses are hard to find].
Response: Thank you for this important comment. We have strengthened the applicability of the study by considering the economic feasibility and practical potential of the study.
Comment4: It is advisable to improve the conclusions in terms of synthesis and fertilization.
Response: Thank you for this valuable suggestion. We have revised the conclusion section (refer to the revised manuscript).

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors

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Competing Interests

No competing interests were disclosed.

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Reviewer Report

6 Views

09 Jan 2026 | for Version 2

Dominic Yellezuome, University of Mines and Technology, Tarkwa, Western Region, Ghana

6 Views Cite this report Responses(1)

Approved With Reservations

There is too much information in the methods paragraph in the Abstract Section, in which some of it can not be found in the Methods Section, such as “This study was conducted experimentally using factorial patterns and a completely randomized 6 × 2 design.”
And some of them are not important to be in the Abstract Section. Such as “Standard techniques were used to measure the physicochemical characteristics of the mixed waste, such as pH, total solids, volatile solids, organic carbon, and moisture. This study was conducted experimentally using factorial patterns and a completely randomized 6 × 2 design. The water displacement method was used to estimate the average amount of biogas generated by a 0.6 L digester.”
These sentences are similar; hence should be merged.

“Biogas production from different types of biodegradable waste is an alternative to fossil fuels for energy consumption and biodegradable waste management. Biogas is a cost-effective, environmentally friendly, and sustainable energy source that provides a reliable method for handling food waste.”
“An innovative solution to increase anaerobic waste digestion yields is codigestion, which is an inexpensive and simple technology that enhances the anaerobic digestion rate by creating a better nutrient balance from the materials mixed to feed the digester, provides positive synergism for bacterial growth, and increases biogas production (Sosnowski et al., 2003; Mata-Alvarez et al., 2000; Mshandete et al., 2004; Leta et al., 2015). Several studies have used co-digestion to increase the rate at which organic matter is converted biologically in the biogas system to improve biogas performance (Huang et al., 2016; Alemayehu, 2014; Mata-Alvarez et al., 2014; Abbas et al., 2021).”
“A diverse range of fungi, bacteria, protozoa, and archaea inhabit the rumen, an anaerobic microbial habitat (Sylvester et al., 2004; Sonakya et al., 2003). The rumen contains a variety of microorganisms, including cellulolytic and methanogenic bacteria (Lopes et al., 2004; Yue and Yu, 2009).”
“Institutions such as universities, agro-industries, and municipalities that produce large amounts of food and fruit-vegetable waste should implement co-digestion systems using these inoculants to improve waste management, lower environmental pollution, and produce renewable energy. Additionally, by offering a cleaner, sustainable alternative for household and industrial energy, expanding this strategy could improve public health, reduce reliance on firewood, and mitigate deforestation.”

Authors cited lists of 3 or more references without proper justification of the relevance of each one. Hence, avoid citing more than two references and outdated references.
“Although there is information on biogas production from organic waste or single inoculums (Alemayehu, 2014; Abayneh et al., 2014; Hammad et al., 2018; Earnest and Singh, 2013) but there is limited reports on methods for increasing biogas generation, particularly those that use rumen fluid and S. cerevisiae.” This paper is not clear in the description of the scientific novelty in comparison to related previously published and referenced in your work below:

“…there are 107,684 residents, comprising 49,893 men and 57,791 women (Aynalem et al., 2014).” These statistics are outdated.
“This study aimed to evaluate the effects of ruminant fluids and S. cerevisiae isolate MUTJ0F (OR209280.1) on biogas generation from various mixed organic wastes co-digested with cattle manure. Various wastes from fruits and vegetables were gathered from the town fruit houses, leftover food from the Debre Markos University student cafeteria, fresh cattle manure (CM) from Monkorer Agroindustry Enterprise, and rumen fluids (RL) from a nearby slaughterhouse and used as activators for biogas production.” These sentences contains repititions in the next paragraph, hence should be avoided.
“… the de-sized cattle manure and food waste were mixed separately with distilled water in a 1:5 (solid waste: distilled water) volume ratio …” What is the ratio between cafeteria leftovers, cattle manure, and fruit and vegetable waste? How was the solid waste measured in volume?
What is the size of the filter used in filtering the rumen fluid?
Some of the citations are not necessary, such as

“Then, different amounts of the filtrate were added to each digester to initiate the reaction (Aurora, 1983; Genet et al., 2018).”
“After calibration, the electrode was submerged in the substrate samples, rinsed with distilled water, and the pH values were recorded (Arogo et al., 2009).”

In subsection 2.5.1, how was the measured empty crucible used in the formula?
In subsection 2.5.2, the authors indicated the measurement of fixed solids, but it was not presented in Table 1.
Authors should be consistent with the way they explain parameters in an equation, whether horizontal or vertical.
The procedure for moisture content determination is the same as that of total solids, so you can indicate the formula of MC there and delete subsection 2.5.4
“After calibration, the electrode was submerged in the substrate samples, rinsed with distilled water, and the pH values were recorded (Arogo et al., 2009).” Are the authors sure this was the sequence used in measuring the pH value?
“The first factor was the dosage of rumen liquid i.e. 0 ml/100 g, 25 ml/100 g, 50 ml/100 g, 75 ml/100 g, and 100 ml/100 g), …” Why is the 150 ml rumen fluid not stated here but in Table 2?
“The study was conducted at room temperature (30°C).” How did the authors maintain this temperature in the room?
“Feed stock was mixed with distilled water to obtain approximately 8% of TS suspension.” Is this information similar to the “1:5 (solid waste: distilled water) volume ratio” indicated in Section 2.3?
In section 2.6, the retention time or duration of the anaerobic digestion was not mentioned.
Section 2.7 should come before Section 2.6. Also, the authors need to provide an image of the three plastic bottles set up for anaerobic digestion, since it was constructed for this study. What is the working volume of the digester?
Sections 2.8 and 2.7 can be merged. Was the biogas measured daily or at what interval?
In Section 3.1, what does the use of “mixed wastes” mean? For example: “The pH of the mixed waste ranged from 6.8 to 7.6, …” Does it mean the mixture of the various feedstock or the individual feedstock?
“The VS/TS ratios of the cafeteria food waste and cattle manure were 78.3% and 91.2%, respectively.” What about fruit and vegetable waste?
“Cattle dung is used to accelerate biogas production by promoting bacterial growth in the digester.” Provide a reference.
“Co-digestion has a positive synergistic effect by neutralizing pH, increasing buffering capacity, reducing the effects of harmful compounds, and supplying more balanced nutrients, such as vitamins, trace metals, and other substances required for microbial growth (Fang, 2010; Aragaw et al., 2013; Jianzheng et al., 2011).” The relevance of this information in the Results and Discussion Section is not clear since it has already been stated in the Introduction Section with different references cited.
“The 12 methane production treatments varied significantly, reflecting variations in the mixed-waste composition and inoculum dosage.” Are the authors sure that the variations in the mixed-waste composition may have caused the significant difference in biogas production?
“This implies that the high anaerobic bacterial concentration in rumen fluid efficiently breaks down organic substrates from mixed waste.” Is it only the rumen fluid that increased biogas production?
“According to the results, the maximum amount of biogas (6900.3 ml) …” Normally, biogas production is evaluated using methane yield (mL/gVS or mL/gTS) to enable comparison with other published studies.
In Table 2, why was only rumen fluid not investigated? The heading “Methane (mean ± SD)”, did the authors measure methane or biogas?
In Figure 1, please plot pH on the y-axis and days on the x-axis. Why plot only T10? It is better to plot all the treatments. Why was the pH measured up to 80 days, but the anaerobic digestion was observed for 60 days, as indicated in Figure 2, the Abstract and Section 3.4?
Figure 2A and B should come before Figure 1.
These sentences could have been verified by plotting the daily biogas production.

“This low pH value was permitted very little methanogenic bacterial activity …”
“This also brings the pH closer to neutral, which makes it easier for methanogenic microbes to multiply and produce methane. Methanogenic bacteria the optimum pH values between 6.8 and 7.2 (Anunputtikul and Rodtong, 2004; Budiyono et al., 2010).”

The authors should clarify which equipment was used for the combustion test, either “a lit matchstick” as indicated in Section 2.9 or “a Bunsen burner” as indicated in Section 3.4. Also, Figure 2C was not well captured to help identify which equipment was used. In section 3.4, it is better use “Figure 2C” rather than “Figure 2”.
“Biodegradation, microbial strength, and biogas generation can all be enhanced by using …” How were biodegradation and microbial strength measured in this study?
Future perspectives or studies could be added to the Conclusion section.
The language must be checked thoroughly.

Some statements are not clear or too long and should be revised. For examples:

Avoid stating the mesophilic condition twice in the abstract section.
"physic-chemical properties" = "physicochemical properties"
Use SI units. For example “hrs” = “h”
These sentences should be merged to improve clarity.

“This increase is due to ammonification processes …” Since this sentence was not verified by measurement, it would be better to express it as “This increase may be due to ammonification processes …”

Is the work clearly and accurately presented and does it cite the current literature?

Partly
Is the study design appropriate and is the work technically sound?

Partly
Are sufficient details of methods and analysis provided to allow replication by others?

Partly
If applicable, is the statistical analysis and its interpretation appropriate?

Not applicable
Are all the source data underlying the results available to ensure full reproducibility?

Partly
Are the conclusions drawn adequately supported by the results?

Partly

Competing Interests

No competing interests were disclosed.

Reviewer Expertise

Anaerobic digestion, pyrolysis and gasification

Respond to this report

Responses (1)

Author Response

18 Apr 2026

Mulugeta Fentahun, College of Natural and Computational Sciences, Department of Biology, Debre Markos University, Debre Markos, 269, Ethiopia

Mulugeta Fentahun
Thanks to Dr. Dominic Yellezuome for your constructive comments. We conducted a number of changes.
I greatly appreciate your feedback and suggestions. Please find my responses to your comments below:

Comment 1: There is too much information in the methods paragraph in the Abstract Section, in which some of it can not be found in the Methods Section. Some of them are not important to be in the Abstract Section.
Response: Thank you for this helpful comment. We have revised the abstract according to your feedback. Refer to the abstract part in the updated manuscript
Comment 2: These sentences are similar; hence should be merged.
Response: Thank you for this observation. We have revised the manuscript by merging similar sentences to improve readability and eliminate redundancy (Refer to the revised manuscript).
Comment 3: Authors cited lists of 3 or more references without proper justification of the relevance of each one. Hence, avoid citing more than two references and outdated references (Refer to the revised manuscript).
Response: Thank you for this constructive comment. We have revised the manuscript by limiting citations and avoiding outdated references (Refer to the revised manuscript).
Comment 4: Although there is information on biogas production from organic waste or single inoculums (Alemayehu, 2014; Abayneh et al., 2014; Hammad et al., 2018; Earnest and Singh, 2013) but there is limited reports on methods for increasing biogas generation, particularly those that use rumen fluid and S. cerevisiae.” This paper is not clear in the description of the scientific novelty in comparison to related previously published and referenced in your work below:
Response: Thank you for this important comment. We have revised the manuscript based on your comments (Refer to the revised manuscript).
Comment 5: There are 107,684 residents, comprising 49,893 men and 57,791 women (Aynalem et al., 2014).” These statistics are outdated.
Response: Thank you for pointing this out. We have updated the demographic information using the most recent and reliable data sources to ensure accuracy and relevance in the manuscript.
Comment 6: This study aimed to evaluate the effects of ruminant fluids and S. cerevisiae isolate MUTJ0F (OR209280.1) on biogas generation from various mixed organic wastes co-digested with cattle manure. Various wastes from fruits and vegetables were gathered from the town fruit houses, leftover food from the Debre Markos University student cafeteria, fresh cattle manure (CM) from Monkorer Agroindustry Enterprise, and rumen fluids (RL) from a nearby slaughterhouse and used as activators for biogas production.” These sentences contains repititions in the next paragraph, hence should be avoided.
Response: Thank you for this comment. We have revised the manuscript to remove the repetitive sentences.
Comment 7: The de-sized cattle manure and food waste were mixed separately with distilled water in a 1:5 (solid waste: distilled water) volume ratio …” What is the ratio between cafeteria leftovers, cattle manure, and fruit and vegetable waste? How was the solid waste measured in volume?.
Response: Thank you for this insightful comment. We have revised the manuscript to clarify the mixing ratios and measurement procedures (Refer to the revised manuscript).
Comment 8: What is the size of the filter used in filtering the rumen fluid?
Response: Thank you for this comment. We have revised the manuscript based on your comments (Refer to the revised manuscript).
Comment 9: Some of the citations are not necessary, such as ○ “Then, different amounts of the filtrate were added to each digester to initiate the reaction (Aurora, 1983; Genet et al., 2018).” “After calibration, the electrode was submerged in the substrate samples, rinsed with distilled water, and the pH values were recorded (Arogo et al., 2009).
Response: Thank you for this comment. We have revised the manuscript by removing unnecessary citations.
Comment 10: In subsection 2.5.1, how was the measured empty crucible used in the formula?
Response: Thank you for this comment. We have revised and clarified the method in subsection 2.5.1 based on your feedback (Refer to the updated manuscript).
Comment 11: In subsection 2.5.2, the authors indicated the measurement of fixed solids, but it was not presented in Table 1.
Response: Thank you for this comment. We have revised the manuscript by include the measured fixed solids in Table 1 or clarified in the manuscript.
Comment 12: Authors should be consistent with the way they explain parameters in an equation, whether horizontal or vertical.
Response: Thank you for this comment. We have revised the manuscript to present all equation parameters consistently in a horizontal format (Refer to the updated manuscript).
Comment 13: The procedure for moisture content determination is the same as that of total solids, so you can indicate the formula of MC there and delete subsection 2.5.4.
Response: Thank you for this suggestion. We have removed subsection 2.5.4 and included the formula for moisture content within the total solids section, streamlining the methods and avoiding redundancy.
Comment 14: After calibration, the electrode was submerged in the substrate samples, rinsed with distilled water, and the pH values were recorded (Arogo et al., 2009).” Are the authors sure this was the sequence used in measuring the pH value?
Response: Thank you for this comment. We have revised the correct sequence and refer to the updated the manuscript.
Comment 15: The first factor was the dosage of rumen liquid i.e. 0 ml/100 g, 25 ml/100 g, 50 ml/100 g, 75 ml/100 g, and 100 ml/100 g), …” Why is the 150 ml rumen fluid not stated here but in Table 2?
Response: Thank you for this comment. We have revised the manuscript to include the 150 ml/100 g rumen fluid level in the text for consistency with Table 2.
Comment 16: The study was conducted at room temperature (30°C).” How did the authors maintain this temperature in the room?
Response: Thank you for this comment. We have clarified in the manuscript that the study was conducted under mesophilic conditions at 38 °C using an oven, and the text has been corrected to fix the typographical error.
Comment 17: Feed stock was mixed with distilled water to obtain approximately 8% of TS suspension.” Is this information similar to the “1:5 (solid waste: distilled water) volume ratio” indicated in section 2.3?
Response: Thank you for this comment. We have clarified in the manuscript that the 8% TS suspension is distinct from the 1:5 ratio described in section 2.3.
Comment 18: In section 2.6, the retention time or duration of the anaerobic digestion was not mentioned.
Response: Thank you for this comment. We have revised section 2.7 based on your comment.
Comment 19: Section 2.7 should come before Section 2.6. Also, the authors need to provide an image of the three plastic bottles set up for anaerobic digestion, since it was constructed for this study. What is the working volume of the digester?
Response: Thank you for this comment. We have revised the manuscript and we have added an image of the three plastic bottle digesters used in this study and the working volume of digester.
Comment 20: Sections 2.8 and 2.7 can be merged. Was the biogas measured daily or at what interval?
Response: Thank you for this comment. We have merged sections 2.7 and 2.8 for clarity and streamlined the methods. We also clarified that biogas production was measured at regular daily intervals throughout the experiment.
Comment 21: In section 3.1, what does the use of “mixed wastes” mean? For example: “The pH of the mixed waste ranged from 6.8 to 7.6, …” Does it mean the mixture of the various feedstock or the individual feedstock?
Response: Thank you for this comment. We have clarified in section 3.1 based on your comments. Refer to the results and discussion parts in the updated manuscript.
Comment 22: The VS/TS ratios of the cafeteria food waste and cattle manure were 78.3% and 91.2%, respectively.” What about fruit and vegetable waste?
Response: Thank you for this comment. We have revised the manuscript based on your comments.
Comment 23: Cattle dung is used to accelerate biogas production by promoting bacterial growth in the digester.” Provide a reference.
Response: Thank you for this comment. We have added a relevant reference. Refer to the updated manuscript.
Comment 24: Co-digestion has a positive synergistic effect by neutralizing pH, increasing buffering capacity, reducing the effects of harmful compounds, and supplying more balanced nutrients, such as vitamins, trace metals, and other substances required for microbial growth (Fang, 2010; Aragaw et al., 2013; Jianzheng et al., 2011).” The relevance of this information in the Results and Discussion Section is not clear since it has already been stated in the Introduction Section with different references cited.
Response: Thank you for this comment. We have revised the results and discussion section and remove the redundant statement.
Comment 25: The 12 methane production treatments varied significantly, reflecting variations in the mixed waste composition and inoculum dosage.” Are the authors sure that the variations in the mixed-waste composition may have caused the significant difference in biogas production?
Response: Thank you for this comment. We have revised the manuscript based on your comments.
Comment 26: This implies that the high anaerobic bacterial concentration in rumen fluid efficiently breaks down organic substrates from mixed waste.” Is it only the rumen fluid that increased biogas production?
Response: Thank you for this comment. We have revised the manuscript based on your comments.
Comment 27: According to the results, the maximum amount of biogas (6900.3 ml) …” Normally, biogas production is evaluated using methane yield (mL/gVS or mL/gTS) to enable comparison with other published studies.
Response: Thank you for this comment. We clarify that our results were reported based on the total biogas volume (mL), and we did not measure total solids or volatile solids after digestion (methane yield (mL/gVS or mL/gTS) in this experiment.
Comment 28: In Table 2, why was only rumen fluid not investigated? The heading “Methane (mean ± SD)”, did the authors measure methane or biogas?
Response: Thank you for this comment. We have clarified that Table 2 presents biogas production and not methane specifically; the heading has been corrected accordingly. Additionally, rumen fluid alone was not included as a treatment because the study focused on co-digestion with mixed wastes to evaluate the synergistic effect of dual inoculants.
Comment 29: In Figure 1, please plot pH on the y-axis and days on the x-axis. Why plot only T10? It is better to plot all the treatments. Why was the pH measured up to 80 days, but the anaerobic digestion was observed for 60 days, as indicated in Figure 2, the Abstract and Section 3.4?
Response: Thank you for this comment. We have revised Figure 1 to plot pH on the y-axis against days on the x-axis and included all treatments for clarity. Additionally, we clarified that pH measurements were continued up to 80 days to monitor post-digestion stabilization, even though the main anaerobic digestion period lasted 60 days.
Comment 30: Figure 2A and B should come before Figure 1.
Response: Thank you for this comment. We have revised the manuscript so that Figures 2A and 2B now appear before Figure 1.
Comment 31: These sentences could have been verified by plotting the daily biogas production.
Response: Thank you for this comment. We have revised the sentences in the updated manuscript.
Comment 32: The authors should clarify which equipment was used for the combustion test, either “a lit matchstick” as indicated in Section 2.9 or “a Bunsen burner” as indicated in Section 3.4. Also, Figure 2C was not well captured to help identify which equipment was used. In section 3.4, it is better use “Figure 2C” rather than “Figure 2”
Response: Thank you for this comment. We have revised the manuscript in the method section and the results and discussion sections.
Comment 33: Biodegradation, microbial strength, and biogas generation can all be enhanced by using” How were biodegradation and microbial strength measured in this study
Response: Thank you for this comment. We have revised the manuscript based on your comments.
Comment 34: Future perspectives or studies could be added to the Conclusion section.
Response: Thank you for this comment. We have revised the conclusion section to include future perspectives.
Comment 35: The language must be checked thoroughly.
Response: Thank you for this comment. We have carefully reviewed and revised the manuscript to improve language, grammar, and clarity throughout the text.

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors

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Competing Interests

No competing interests were disclosed.

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Reviewer Report

23 Views

19 Aug 2025 | for Version 1

Jovine Kamuhabwa Emmanuel, Chemistry, University of Dar es Salaam, Dar es Salaam, Dar es Salaam, Tanzania

23 Views Cite this report Responses(1)

Not Approved

Title

The title captures the content of the current work.

Abstract

Introduction

Materials and methods

Proper details and step after step must be provided for readers to follow. Authors need to take time and re-do it properly. Other comments are found in the main document.

Results and discussion

Results are not well organized and discussed with previous work. Authors need to re-think on how they can organize these data for publication. Other comments are found in the main document.

Conclusions and recommendations

This section is not well written thus, must be re-written for clarity. Only key findings and recommendation must be presented and not otherwise. Other comments are found in the main document.

General comment

Is the work clearly and accurately presented and does it cite the current literature?

No
Is the study design appropriate and is the work technically sound?

Yes
Are sufficient details of methods and analysis provided to allow replication by others?

Partly
If applicable, is the statistical analysis and its interpretation appropriate?

Not applicable
Are all the source data underlying the results available to ensure full reproducibility?

Partly
Are the conclusions drawn adequately supported by the results?

Partly

Competing Interests

No competing interests were disclosed.

Reviewer Expertise

Catalysis, materials science and bioenergy

Respond to this report

Responses (1)

Author Response

29 Dec 2025

Mulugeta Fentahun, College of Natural and Computational Sciences, Department of Biology, Debre Markos University, Debre Markos, 269, Ethiopia

Mulugeta Fentahun
Dr. Jovine Kamuhabwa Emmanuel thank you very much for your insightful comments and the time you dedicated to review.
We greatly appreciate your feedback and suggestions. We provide a detailed response to each comment, along with the corresponding changes made in the revised manuscript below:

Title:

Comment: The title captures the content of the current work.
Response: Thank you for your positive feedback.

Abstract Revision:

Comment: The abstract has no information on the study, methodology used, and key findings and recommendations based on the findings. Authors must re-write this to reflect the current work.
Response: Thank you for your insightful comment. We have thoroughly revised the abstract part in response to your suggestions (see the revised manuscript).

Introduction Revision:

Comment: The section has not been written properly and is not easy to follow and understand. Authors must write this in a scholarly manner to reflect an article for publication. The novelty is not well featured; thus, authors must reveal the novelty of the work.
Response: We sincerely thank the reviewer for your constructive feedback. We have thoroughly revised the introduction section to improve clarity, coherence, and scholarly manner. Additionally, we have clearly highlighted the novelty of the study by emphasizing its unique contributions in the revised manuscript (refer to the revised manuscript).

Methodology Revision:

Comment: Proper details and step after step must be provided for readers to follow. Authors need to take time and re-do it properly.
Response: Thank you for this valuable observation. We have substantially revised the materials and methods section to improve clarity, completeness, and reproducibility. The updated version now provides detailed, step-by-step procedures for the experimental work, enabling readers to follow the methodology accurately and enhancing the scientific rigor of the manuscript (see the revised manuscript).

Results and Discussion Revision:

Comment: Results are not well organized and discussed with previous work. Authors need to re-think on how they can organize these data for publication.
Response: We sincerely thank the reviewer for your constructive feedback. We have carefully revised the results and discussion section to enhance clarity and coherence. The revised version enriched with up-to-date citations (recent literature) and emphasizes the key findings. Please refer to the updated section in the revised manuscript.

Conclusions and recommendations Revision:

Comment: This section is not well written thus, must be re-written for clarity. Only key findings and recommendation must be presented and not otherwise.
Response: Thank you for your insightful comment. We have revised the conclusions section to clearly highlight the study’s key findings and recommendation. Please see the updated section in the revised manuscript.

General comment:

Comment: The manuscript must benefit from a serious English Language editing before being indexed.
Response: We sincerely thank the reviewer for the valuable suggestion regarding the language quality of our manuscript. We have thoroughly revised the manuscript to improve English clarity, grammar, and readability.
Comment: The manuscript must be enriched with up-to-date citations which are available in the literature.
Response: Thank you for your comments. We have updated the manuscript by incorporating recent literature, as suggested (see the revised manuscript).

Thank you once again for your valuable feedback. Your comments have significantly contributed to improving the quality of this paper.
Best regards,
Authors

View more View less

Competing Interests

No competing interests were disclosed.

Alongside their report, reviewers assign a status to the article:

Approved - the paper is scientifically sound in its current form and only minor, if any, improvements are suggested

Approved with reservations - A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.

Not approved - fundamental flaws in the paper seriously undermine the findings and conclusions

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Enhancing biogas production from co-digestion of organic wastes mixed with cattle manure using rumen fluid and Saccharomyces cerevisiae isolate MUTJ0F

Abstract

Background

Methods

Result

Conclusion

Keywords

Revised Amendments from Version 2

1. Introduction

2. Methods

2.1 The study area

2.2 Yeast strain used in experiments

2.3 Substrate collection and preparation

2.4 Preparation of inoculums

2.5 Analysis of the physicochemical properties of the substrate

2.6 Experimental set up

2.7 Construction of the anaerobic digesters for batch system

2.8 Burning test

2.9 Data analysis

3. Results and Discussion

3.1 Analysis of the physicochemical properties and composition of the different substrates

Table 1. Physicochemical properties of different substrates (mean ± SD).

3.2 The effect of rumen liquid and S. cerevisiae isolate MUTJ0F on biogas production

Table 2. The effect biogas production on 12 treatments used in anaerobic digestion of mixed wastes combinations with rumen fluid and S. cerevisiae isolate MUTJ0F doses (ml).

Figure 1. Biogas production.

3.3 pH variations in digestors during digestion

Figure 2. pH variation during the digestion process.

3.4 Combustibility of biogas

Figure 3. Combustibility of biogas.

4. Conclusion

Author contribution statement

Consent for publication

Ethical approval

Data availability statement

Underlying data

Acknowledgments

References

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