Improving Anaerobic Digestion Efficiency of Animal Manure Through Ball Milling Pretreatment

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors presented a thesis of the possibility of more efficient manure management in terms of increased biogas production efficiency. The following comments are made:

Manure from dairy production was used for the study, how was the homogeneity of samples for incubation ensured after and without the use of ball milling treatment?

Was the uniform moisture content of the milled material ensured during the pre-treatment?

Was care taken to ensure equal chemical and biological conditions of treated manure and raw manure during anaerobic digestion during incubation?

In line 118, the abbreviation PCM is not described.

In Figure 1, there is no indication of statistical differences between the combinations.

Table 3 lacks statistical elaboration of the results which makes it impossible to infer the results, as the authors declare in the text in section 3.1.2.

There is no clear conclusion that ball milling affects the rate of carbon release from manure under anaerobic digestion, and the content of lignino-cellulosic compounds which could confirm the higher efficiency of biogas formation.

The authors did not summarize how the proven manure treatment technique could be applied to medium- and small-scale farms, as mentioned in the introduction.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

1. Line 9-10: The sentence "Anaerobic digestion (AD) offers a promising pathway for converting animal waste into biogas, improving waste management practices and generating renewable energy" it is better to split into two sentences.
2. Line 16: In "1-hour ball mill pretreatment", consider adding a hyphen for consistency: "1-hour ball-mill pretreatment".
3. Line 44: "14.2-32.3%" and similar ranges throughout the paper should use en-dashes rather than hyphens: "14.2–32.3%".
4. Line 49: "breaking the covalent bonds" would be more precise as "cleaving the covalent bonds".
5. Line 52: Consider rephrasing "being used" to "are used" for more direct language.
6. Line 71: "TRM" appears to be a typo and should be "TMR" (Total Mixed Ration).
7. Line 78: Consider adding "thoroughly" after "dried" for methodological clarity.
8. Line 82: The hyphenation in "ball-to-biomass" should be consistent throughout the paper.
9. Line 89: Consider adding "by weight" after "5%" for clarity.
10. Line 90: Missing "were" before "used during the pretreatment".
11. Line 184: The phrase "has different influences" would be clearer as "has distinct effects".
12. In the abstract, the authors mention a 20% increase in biogas production but later show varying percentages (21.91%, 23.12%, etc.) across different treatments. It would help to be more precise and consistent with these numbers.
13. The methods section mentions storing manure at -20°C but doesn't address potential impacts of freezing on microbial communities or manure properties. This could affect the results.
14. The authors used a ball-to-biomass ratio of 3:1 but don't justify this choice.
15. The experimental design shows four treatments. Please explain why 0.5% was chosen as the activated carbon concentration.
16. The ball milling mechanism of action isn't fully explained. Please, how exactly does particle size reduction lead to increased biogas production?
17. The microbial community analysis doesn't address potential temporal changes over the four HRTs.
18. The conclusion suggests further studies are needed. Please, specify what aspects need further investigation.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

Home Composting: A Sustainable Solution at Community Level

 

Manuscript ID: “agronomy-3417413”

Titled: “Improving Anaerobic Digestion Efficiency of Animal Manure 2 Through Ball Milling Pretreatment”

Journal: “Agronomy”

This manuscript requires significant revision throughout. Numerous issues were identified with language, grammar, punctuation, and overall structure. The clarity and flow of the text need substantial improvement. A thorough revision and careful editing are essential to enhance the readability and impact of the manuscript.

Here are specific comments:

Introduction:

1.      The Introduction should be restructured to begin with a clear statement of the research problem and then logically transition to the study's objectives and rationale.

2.      The manuscript lacks sufficient and up-to-date citations throughout all sections.

3.      The novelty of this study is not clearly defined. The manuscript needs to explicitly state the unique contributions of this research to the existing body of knowledge. For example, does this study investigate new composting methods, utilize novel materials, or provide new insights into the characterization of compost? The authors should clearly articulate what distinguishes this research from previous work in the field and how it advances the understanding of home composting.

 

Materials and methods

4.      The Materials and Methods section requires significant clarification. The description of experimental procedures lacks sufficient detail and clarity in several areas. For example, the pre-treatment methods for animal manure should be described more precisely. The monitoring and experimental procedures need to be presented in a more logical and organized manner, with clear descriptions of all steps involved.

Results and discussion

5.      The Results and Discussion sections require significant improvement. The presentation of results lacks clarity and depth. Key findings should be concisely stated and supported by appropriate figures and statistical analyses. The discussion section needs to go beyond simply describing the results. It should:

·         Interpret the findings in the context of existing literature on home composting.

·         Discuss the implications of the study for the feasibility and effectiveness of home composting.

·         Compare and contrast the results obtained for P1 and P2, analyzing the potential reasons for the observed differences.

·         Critically evaluate the limitations of the study and suggest areas for future research. The current discussion relies heavily on descriptive statements. It needs to be more analytical and incorporate deeper insights into the composting process. Finally, the connection between the results and the discussion needs to be strengthened. The authors should strive to provide a more insightful and nuanced interpretation of their findings.

 

6.      In the discussion, the manuscript notes that the RM-Ctrl group exhibited a higher abundance of both the Firmicutes phylum and Methanobrevibacter genus compared to the other three groups, suggesting a potential link to the relatively higher NH3-N levels observed in this group (lines 374-375). However, the rationale behind this connection is not clearly articulated, leaving the relevance of these findings somewhat unclear.

 

Conclusion

7. In the conclusion, the statement on lines 386-388 mentions that “TM group showed significant effects on the Methanosaeta genus, and several other bacterial groups, which influence nitrogen metabolism of the microbial communities for ammonia production”, however, this claim is not sufficiently supported earlier in the manuscript, as there is no prior discussion on how the TM group specifically affects nitrogen metabolism or ammonia production.

 

General comments

·         The abbreviations “PCMs” (line 118) and DIET (line 355) are used without prior clarification, which may cause confusion for readers unfamiliar with these terms. Add a list of abbreviations

·         The paper does not include any comparison with previous studies in the field.

 

Comments on the Quality of English Language

This manuscript requires significant revision throughout. Numerous issues were identified with language, grammar, punctuation, and overall structure.

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

Comments and Suggestions for Authors

good research for potential use in practice.

biogas production rate per VS added may not be thought to be optimal, only arround 260-290, relatively low. Please double check about it.

Comments for author File: Comments.pdf

Author Response

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Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Agreed with the revisions made by the authors.