Biomethanation of Crop Residues to Combat Stubble Burning in India: Design and Simulation Using ADM1 Mathematical Model
Round 1
Reviewer 1 Report
The manuscript provides a perspective of biogas energy production from the different crop residues in India utilizing a mathematical model. The aim of the study is interesting and relevant considering the problems caused by stubble burning and provides possible methods for utilizing stubble as a (clean energy) resource. The approach suggested in the manuscript by considering the small-scale farmers is feasible, in view that stubble burning is a farmer-related issue. The manuscript is suitable for publication, after the authors have addressed the following comments and questions.
- Page 3, line 101: “… excellent soil conditioners recycling and retaining the nutrients " Which "nutrients" are meant? Digestate is commonly known for containing less organic C than the feedstock.
- Page 4, line 148: Mention the estimated percentage increase in biogas generation during co-digestion as animal husbandry is a vital component of the agrarian community in India.
- Page 7, line 269: What qualifies the ADM1 model to be better than the other mathematical models? This has to be specified when claiming ADM1 model to be the most competent model.
- Page 8, line 312: What about the C: N ratio when co-fermenting the residues with nitrogen-rich manure? The authors are suggested to provide an insight on the role of C: N ratio during biogas generation and in maintaining process stability.
- Page 10, line 364: The authors are recommended to also add recent updates on the formation of the Renewable Gas Association of India (RGAI).
- Page 10, line 383: Mention the limitations when utilizing stubble for biogas generation in the conclusion section.
- The introduction can be further improved by focusing on the problems faced by India because of stubble burning.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
“Biomethanation of crop residues to combat stubble burning in India: Design and simulation using ADM1 mathematical model” is a good work.I will recommend the paper for publication with minor changes. (Please see the attachment.)
Comments for author File: Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
The authors focus on a possible solution to an important and practical problem that affects the natural environment and human health in the research context. The mathematical modelling of biogas production provides valuable insights and induce recommendations for future biogas plant implementation to generate energy from waste. Nevertheless, there are opportunities through which the quality of the paper could be increased, as follows:
- In the introduction, the authors should briefly clarify the followed terminology based on definitions from the literature, regarding biogas and biomethane, biogas production, biomethane production, biomethanation. It should be emphasized that biogas should not considered equal to biomethane. In connection with this, it could be highlighted that biomethane production from biogas is possible through different methods of biogas upgrading or power-to-gas / power-to-methane processes which allow the conversion of CO2 into CH4, as well (see e.g., https://doi.org/10.3390/en14185591).
- I suggest a more rigorous approach regarding quantitative scientific excellence during the paper with some text extensions. For example, in the introduction, the research gap must be explicated better. Based on the research gap, the research question / goal should be clearly articulated. Moreover, based on the previous literature findings, a working hypothesis / more working hypotheses should be defined.
- The first paragraph of Section 1.3. seems to be more related to Section 3.
- At the end of the introduction, contributions and the structure of the paper could be also outlined shortly.
- In Section 3, to demonstrate the solid methodological ground, those steps could be highlighted that were undertaken to improve generalizability, reliability and validity in a quantitative sense.
- I strongly suggest discussing the results in a broader sense, as well, to contextualize the findings of the research, for example, how the results could be interpreted from the aspect of recent circular economy and biomethanation research, and discussing the opportunities and limitations of further developments based on biogas production, concerning the other important challenges of sustainable transitions, e.g., renewable electricity generation, short-term and long-term energy storage, power-to-methane processes, decarbonization, based on articles published e.g. in other MDPI journals (e.g., Energies, Sustainability)
- In the Conclusions section, the authors could reflect on the hypothesis/hypotheses by accepting or rejecting it/them; practical and theoretical contributions could be articulated, moreover, limitations and future research directions are also missing now.
- Reference formats are incorrect somewhere, e.g., in line 42, 48, 241, 355
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Thank you for considering the comments and the modifications. In my opinion, the key issues are properly explained now.
