Syntrophic Jiont of Sulfate-Reducing Bacteria and Hydrogen-Producing Acetogen Stimulated Methane Production from Waste Activated Sludge Digestion

Round 1

Reviewer 1 Report

This article investigates enhancing methane production from waste activated sludge (WAS) via the synergistic interactions of sulfate-reducing bacteria (SRB) and hydrogen-producing acetogen (HPA). It primarily aims to optimize the dosage and combination of HPA and SRB to stimulate methane production effectively. By pre-treating WAS with coupled Fe(VI)/S(IV) oxidation, the research examines how these microbial consortia can address the challenges of hydrolysis and acetogenesis that typically impede methane production in anaerobic digestion processes. The results indicate that a balanced dosage of HPA and SRB not only facilitates the breakdown of complex organic substances in sludge but also improves the subsequent stages of acidogenesis and methanogenesis, significantly enhancing methane yield. This study provides crucial insights into the potential implementation of innovative biotechnological applications for energy recovery from waste treatment processes.

Areas requiring corrections or improvements:

Statistical analysis:

The article does not specify the software used for statistical analysis, including the Pearson correlation matrix calculations. This detail is essential for verifying the analysis methods and results.

Results and discussion:

The discussion could be expanded to consider the broader implications of the findings. It would be beneficial to compare these results with existing technologies more thoroughly and discuss potential issues related to scaling up the process (refer to lines 178-208, 234-254 in the document).

Citation of prior research:

In line 241, the article mentions previous research without clarifying whether this research has been published. Including references or acknowledging unpublished data would provide greater transparency and allow readers to verify the findings.

Technical terms and jargon:

The use of technical language in the article might be challenging for non-specialists. Terms such as "syntrophic joint" and "canonical correspondence analysis" need clearer definitions or explanations to make the content more accessible to a broader audience.

Conclusions:

The conclusions section should more directly reflect the objectives introduced at the beginning of the paper. It would be more effective to summarize how the findings address the initial research questions and clearly state the novel contributions of this study to the field.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The reviewed text is devoted to interesting and important, both from a scientific and practical point of view, research, both scientifically and practically, of anaerobic digestion of waste activated sludge with Fe(VI)/S(IV) pretreatment and mutualism among hydrogen-production acetogen – sulfate-reducing bacteria processes and aceticlastic methanogenic bacteria.

However, a careful reading of the text prompted the reviewer to make the following comments:

1.      The reaction equations quoted in L59 and L82 are unbalanced. The inquisitive reader will find these equations in the provided source data, where they are balanced and sound different!

2.      The authors use the abbreviated notation: "PF+Na2SO3". Nowhere in the text do they expand on the abbreviation "PF". A reader less familiar with the content will not know that it means: "potassium ferrate", right?

3.      The text contains more unexplained (undeveloped) acronyms, e.g. L220 - "PDS", L317 - MEN and OTU. Acronyms should be expanded upon first use.

4.      In L223, the authors refer to Table 1 and Column 3 marked "Rm/mL CH4/(g Vss*d)" They call this quantity "methane production potential". However, in equation (1), this variable is denoted "Pm" while Rm is the "kinetic parameter of methane yield".

5.      In L354, the authors write about "narrower angle between SCFAs and methane than that of HAc and methane indicated that HAc" referring to Figure 4A. In Figure 4A, both vectors (SCFA and HAC) coincide and do not form any visible angle. Hence, further conclusions from L355-357 are unjustified without providing numerical values.

6.      In L180, the authors compare the D50 values of sewage sludge. Unfortunately, neither the equipment nor the measurement methodology used to determine the particle size distribution of sewage sludge (and hence the D50 value) is provided anywhere.

7.      Drawings should be placed as close as possible to the first reference to them. Unfortunately, they are up to 3 pages further (Figure 1), which makes the text difficult to read.

8.      Figure 4 is too small and difficult to read, especially Fig. 4B.

9.      Perhaps it would be worthwhile in the "conclusions" section to indicate the perspectives of development and application of the obtained results.

The reviewer believes the text is exciting and contains essential and potentially helpful research results for other scientists. However, it requires thorough revision and improvement by the indicated comments.

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Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

In its present form, with corrections and additions, the text is suitable for publication.

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