Review Reports - Synergistic Promotion of Direct Interspecies Electron Transfer by Biochar and Fe₃O₄ Nanoparticles to Enhance Methanogenesis in Anaerobic Digestion of Vegetable Waste

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study reports the preparation of nano Fe₃O₄ particles with an inverse spinel structure, loaded into biochar (Fe₃O₄@BC). In a continuous stirred tank reactor (CSTR) anaerobic fermentation system for vegetable waste, the addition of 200 mg·L⁻¹ Fe₃O₄@BC improves system stability under high organic load and enhances gas production rates. Microbial analysis showed that Fe₃O₄@BC promotes direct interspecies electron transfer, increasing microbial diversity and abundance. The question is, did the authors investigate the stability of this composite material? Deposition may leave two separate phases, and FTIR analysis should confirm the formation of some novel bands of interaction between BC and magnetite. A separate analysis of the influences of both constituents in the electron transfer process should be evaluated. Error bars should be included in each set of results. There seem to be no significant differences among different fermented samples. Novelty should be highlighted more in the Introduction part. I recommend a minor revision.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript needs major revisions. The voice in the manuscript needs further modification.

“3.009L L⁻¹ d⁻¹” The unit is wrong. Please rewrite the abstract.

The novelty and gap in the Introduction need to be further condensed.

Please add specific microbiological analysis methods. Also, please add the data analysis in the manuscript.

The author should create a separate group for iron oxide.

Why did the author only conduct the final microbial analysis and dynamic changes? The changes in microorganisms are more indicative of the problem.

Why do archaea and bacterial communities have the same genus? This may be incorrect.

Suggest adding a section on strengthening mechanisms

The caption in this study is too simple, please revise it again. The references are too old, please update the most recent ones. These references may be helpful to the author.

Biochar application in anaerobic digestion: Performances, mechanisms, environmental assessment and circular economy

New insight into effects of waste scrap iron on sludge anaerobic digestion: Performances, microbial community, and potential metabolic functions

Comments on the Quality of English Language

The English could be improved to more clearly express the research.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Dear authors, I have read the article and believe that after making some corrections, your article can be published in the journal Fermentations.

1. It is desirable to add the aim of the study, the methods used in the abstract, as well as the practical value of the research.

2. At the end of the Introduction section, it is necessary to precisely define the Research Gap, the main aim, and the study's main objectives.

3. The abbreviations in Table 1 should be defined.

4. In the Material and Methods section, it is necessary to add a flow chart of the study.

5. The characteristics of the CSTR Reactor should be given in the table.

6. In the Results and Discussion section, it is necessary to add a mathematical description of the results obtained.

7. Based on the results shown in Figures 6, 7, 8, and 9, it is necessary to perform a kinetic analysis to obtain reaction rate constants, pre-exponential factor values , and activation energies. This would significantly enhance the scientific aspect of the work.

8. Figure 11 is best presented in table form to better define quantitative indicators.

9. It is necessary to compare the results obtained with those obtained by other authors.

10. In the Conclusion section, it is necessary to add limitations and plans for future research.

11. In the References section, it is necessary to add a more significant number of publications from 2023-2025.