The Impact of Bacteria on Nitrous Oxide Emission from Wastewater Treatment Plants: Bibliometric Analysis

Round 1

Reviewer 1 Report (Previous Reviewer 3)

Comments and Suggestions for Authors

The manuscript provides a thorough assessment of the influence of bacteria on nitrous oxide (N2O) emissions in wastewater treatment plants (WWTPs), encompassing research conducted from 2000 to 2023. It tackles a significant environmental concern with both clarity and depth. I recommend acceptance.

Comments on the Quality of English Language

The English language quality is good, but it requires some refinement for better clarity and professionalism.

Author Response

Comments and responses

 

The manuscript provides a thorough assessment of the influence of bacteria on nitrous oxide (N₂O) emissions in wastewater treatment plants (WWTPs), encompassing research conducted from 2000 to 2023. It tackles a significant environmental concern with both clarity and depth. I recommend acceptance.

Response: We thank you for your positive feedback and potential contributions to this manuscript

 

The English language quality is good, but it requires some refinement for better clarity and professionalism.

Response: We revised the manuscript to enhance clarity and structure and collaborated with a native speaker to ensure professionalism.

Reviewer 2 Report (Previous Reviewer 1)

Comments and Suggestions for Authors

Necessary corrections have been made.

Author Response

Comments and responses

 

Necessary corrections have been made

Response: We are grateful for your constructive comment, this encourages us to be more productive and to keep learning from our seniors and our mistakes.

Reviewer 3 Report (New Reviewer)

Comments and Suggestions for Authors

The authors must address the following:

 

1. Strengthen the Rationale: Provide a clear and compelling justification for the use of a bibliometric approach and how this approach will contribute to a deeper understanding of the research field.
2. Enhance the Methodology: Provide a detailed and transparent description of the methods employed, including specific inclusion/exclusion criteria for document selection, data cleaning procedures, parameters used in each bibliometric software (CiteSpace, VOSviewer, Bibliometrix), and the rationale for selecting those parameters. Address how the results from different analyses were synthesized and integrated.
3. Develop a Clear Narrative: Reorganize the paper to develop a cohesive storyline that integrates the different findings. 
4. Resolve Contradictions: Provide a thorough explanation for the discrepancies between Figures 2a and 3, and between Figures 4a and 4b, offering possible reasons for these inconsistencies and suggesting how these issues could be addressed in future research.
5. Improve the Discussion: The discussion section needs a major revision to provide more in-depth interpretations and analyses of the bibliometric results. The authors should systematically compare their findings with those of previous studies and thoroughly discuss the implications of their findings for the field.
6. Strengthen the Synthesis of Findings: Clearly demonstrate how the results from different analyses (co-occurrence networks, cluster analysis, co-citation analysis) collectively contribute to a more comprehensive understanding of the research field.

Comments on the Quality of English Language

Many typos and grammatical mistakes are found in the paper.

Author Response

Comments and responses

Thank you for your insightful and detailed feedback on our manuscript. We have considered your advice and have made adjustments accordingly.

1. Strengthen the Rationale:Provide a clear and compelling justification for the use of a bibliometric approach and how this approach will contribute to a deeper understanding of the research field.

Response: In brief phrases, we laid out precisely why we implemented bibliometrics and highlighted how it considerably contributes to a deeper, more objective understanding of a research subject (lines 71-73). It shows that by systematically and quantitatively assessing numerous features, bibliometrics establishes the subject's relevance in the field of study. The investigation will provide insights into bacterium activities in WWTPs, allowing researchers to determine their future steps accordingly.

2. Enhance the Methodology:Provide a detailed and transparent description of the methods employed, including specific inclusion/exclusion criteria for document selection, data cleaning procedures, parameters used in each bibliometric software (CiteSpace, VOSviewer, Bibliometrix), and the rationale for selecting those parameters. Address how the results from different analyses were synthesized and integrated.

Response: We modified the manuscript and improved the methodology section based on your recommendation to clarify data manipulation, bibliometric techniques, and adjustments for significant outcomes. We incorporated how the importing of data in different formats according to tools and ways of learning them before analysis

3. Develop a Clear Narrative:Reorganize the paper to develop a cohesive storyline that integrates the different findings. 

Response: The suggestion is considered in all modifications we make to this manuscript, notably on the methodology, results and discussion sections, according to other provided comments.

4. Resolve Contradictions:Provide a thorough explanation for the discrepancies between Figures 2a and 3 and between Figures 4a and 4b, offering possible reasons for these inconsistencies and suggesting how these issues could be addressed in future research

Response: As recommended, we incorporated a full discussion of this aspect. Kindly consult the discussion section in the revised version of our manuscript (Line 335-342) for the rationale for the differences and how to address that issue. Countries and institutions frequently prioritize research that aligns with national or regional needs. In contrast, co-authorship collaborations reveal networks within the research community, especially those who work within the same research group. However, all of them have the same purpose of strategically informing future studies of major literature information, which is revealed by keywords and citation concepts. Thus, the overall Comparison should be done from these analysis techniques.

5. Improve the Discussion:The discussion section needs a major revision to provide more in-depth interpretations and analyses of the bibliometric results. The authors should systematically compare their findings with those of previous studies and thoroughly discuss the implications of their findings for the field.

Response: We appreciate your suggestion to improve discussion sections. After checking similar studies and Considering your suggestions, we made a significant revision to this section on essential aspects of interpretation and emphasized study contribution as well as eliminating bias.

6. Strengthen the Synthesis of Findings:Clearly demonstrate how the results from different analyses (co-occurrence networks, cluster analysis, co-citation analysis) collectively contribute to a more comprehensive understanding of the research field.

Response: Although we were focusing on the pathways of N₂O emission from bacteria activities in wastewater treatment plants, we agree that it is crucial to strengthen the findings of our research. We have added several points illustrating the contribution of our findings to the understanding of this research subject, especially in the results section (Lines 226-229) and discussion section (lines 335-351 and 411-415). Co-occurrence and clustering analysis provide a thematic overview, demonstrating which topics are central and how they relate to one another. Researchers can differentiate across subfields, discover dominating research areas, and comprehend how different topics are arranged.

Reviewer 4 Report (New Reviewer)

Comments and Suggestions for Authors

This manuscript studied is The Impact of Bacteria on Nitrous Oxide Emission from Wastewater Treatment Plants: Bibliometric Analysis. This work is interesting, which is a significant advancement over existing knowledge, but it needs improvements before considering for publication. The publication is recommended, subjected to revision as mentioned below in comments to the authors:

1.     Highlights are necessary for this journal. Please provide to provide a visual summary of the main findings of the study.

2.     A graphical abstract is recommended in this paper.

3.     why you haven't identified the types of bacteria influencing Nitrous Oxide Emission?

4.     Please add the geographical location of all institutes in the Figure 3.

5.     Please add the impact factor for journal in Figure 1.

6.     Figures 5 and 6 require further explanation and discussions.

7.     Figure 7 is strange. It is unnecessary in a scientific review. Perhaps, high-quality image and specific data should be supplied.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 5 Report (New Reviewer)

Comments and Suggestions for Authors

Summary and general comments

This study involves a bibliographic analysis of WWTP related to bacterial nitrification and denitrification. Overall, the manuscript seem alright, however, there are a lot of minor errors. There are some sections that are not very clear and need improvement. Please see the specific comments below for details.

 

Specific Comments

 

1.   Recheck the first paragraph where authors are assigned year to the Environmental Protection Agency and IPCC. Citation error? Recheck the manuscript for a similar error.

2.   Line 62. The common practice when mentioning the author's name only requires the last name to be mentioned instead of the full name. Recheck the manuscript for a similar error.

3.   Introduction. Some of the species names of bacteria involved can be added for a more complete discussion.

4.   Line 92. Does “Database with 172 samples” mean that the authors compiled only 172 rows of references for the analysis?

5.   Section 2.2 Software version should be mentioned.

6.   The year coverage of the WoS only needs to be mentioned once instead of being mentioned in the introduction and repeated in the method.

7.   Section 2.2. Spelling errors for the software name Bibliomtrix are observed.

8.   Line 104. Is Biblioshiny Web another app?

9.   It is unclear what data was collected by the authors. Does the preprocessing involve only manual removal of duplicate references? What are pruning configuration and time slicing?

10.             English language: use “it is” instead of “it’s”. Recheck the manuscript for a similar error.

11.             Figure 2. The Singapore line is hidden behind the China bubble and is not visible. Consider having a different colour.

12.             Table 1. Do specify if these citation counts include/exclude self-citation.

13.             Line 294-318. Detection of mixed citation formatting. Both author(year) + square bracket [references] are used in the same paragraph.

14.             The lack of explanation in the discussion section is a concern. Commanox, which refers to complete ammonia oxidation, was not described. Readers without biological backgrounds will not understand the meaning of Nar, nir, nor minus nos.

15.             Lines 414 to 422 is difficult to understand the flow of ideas and should be rearranged.

Comments on the Quality of English Language

see specific comments to authors

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report (New Reviewer)

Comments and Suggestions for Authors

I am sorry to say that your rebuttals are not convincing.

Comments on the Quality of English Language

NIl

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 5 Report (New Reviewer)

Comments and Suggestions for Authors

There are a lot of improvements after a revision.

Author Response

We thank you for your positive feedback and potential contributions to this manuscript.

Round 3

Reviewer 3 Report (New Reviewer)

Comments and Suggestions for Authors

Thank you for the opportunity to review the revised manuscript “The Impact of Bacteria on Nitrous Oxide Emission from Wastewater Treatment Plants: Bibliometric Analysis.” While the topic is important, this revised manuscript is not a successful effort as many fundamental issues remain unresolved.

1. Lacking the justification for this study

The authors work very hard to establish the importance of the topic by emphasizing the significant role of bacteria in nitrous oxide (N₂O) emissions from wastewater treatment plants (WWTPs) and its implications for climate change and greenhouse gas mitigation. While this effectively underscores the relevance of the subject, the mere importance of the topic is not a sufficient justification for conducting this study. Furthermore, numerous previous reviews have already covered this subject extensively. The following studies, among others, illustrate this: An et al. (2024; https://doi.org/10.1016/j.biortech.2022.128144), Chen et al. (2020; https://doi.org/10.1016/j.watres.2020.115554), Duan et al. (2017; https://doi.org/10.1016/j.watres.2017.06.034), Duan et al. (2021; https://doi.org/10.1021/acs.est.0c05781), Kampschreur et al. (2009; https://doi.org/10.1016/j.watres.2008.10.026), Law et al. (2012; https://doi.org/10.1039/C1EM10067C),  Lee et al. (2022; https://doi.org/10.1016/j.biortech.2022.128196), Massara et al. (2017; https://doi.org/10.1016/j.scitotenv.2017.02.207), Ni et al. (2015; https://doi.org/10.1016/j.watres.2015.08.049), Vasilaki et al. (2019; https://doi.org/10.1016/j.watres.2019.05.068). 

Alarmingly, the authors fail to acknowledge or engage with these prior reviews. I don’t know whether the authors are unaware of or have deliberately omitted these reviews. Nevertheless, the authors fail to position their research in the broader scientific discourse. Without addressing previous reviews, this study does not clarify whether it fills a gap or simply reiterates known findings using bibliometric methods. This lack of engagement undermines the study’s credibility and raises doubts about whether it makes a meaningful contribution to the field.

 

2.  Problematic methodology

Beyond the lack of justification, the study fails to demonstrate methodological rigor, particularly in its bibliometric approach. Several critical issues undermine the quality and reliability of the analysis. First, the data querying strategy is problematic and may not serve the claimed purposes of this paper. First, the use of “nitrous oxide” AND “emission” is unnecessarily limiting, as nitrous oxide (N₂O) is inherently a gas, making "emission" redundant. By requiring the presence of "emission" in the documents, the search may have missed those studies that discuss N₂O production or nitrogen cycling in wastewater treatment without explicitly using this term. Second, the use of “wastewater treatment plant” (WWTP) strictly refers to a kind of faculty (or infrastructures); the better choice is "wastewater treatment," which refers to the process. The latter includes the former but not vice versa. Third, the authors should also include "sewage treatment," which is an alternative to “wastewater treatment.” Otherwise, the paper will likely omitt those studies focusing on N₂O emissions but use different terminology. Fourth, the wildcard usage in “nitrous oxide*” is unnecessary, as N₂O has no commonly used suffix variations, meaning it does not contribute to expanding the search. The above shortcomings may have led to an incomplete dataset that reduces the comprehensiveness of the bibliometric analysis. Boolean refinements are necessary to ensure the coverage and comprehensiveness of the literature retrieval.

Second, the study does not clearly define the criteria for inclusion and exclusion of documents. Therefore, it is difficult to assess the potential biases in the dataset. While the authors mention that 172 documents were included, they do not specify how many documents were initially retrieved or what filtering process was applied beyond duplicate removal. The authors do not justify why articles, reviews, and conference proceedings are included, but other document types, such as book chapters, dissertations, and technical reports, are excluded. It is also unclear if non-English studies were considered. Without transparency on what was included or excluded and why, the reliability of the findings may be compromised.

Third, another concern is the issue of eligibility (Moher et al., 2009; https://doi.org/10.1136/bmj.b2535). Because a document meets the criteria of data querying, it is not necessarily a relevant document.  The absence of manual screening for relevance raises concerns about whether all retrieved documents genuinely align with the study’s objectives. 

Fourth, data cleaning is also another important issue. Before the bibliometric analysis is performed, the dataset should be cleaned and calibrated by eliminating inconsistent thesaurus terms, e.g., singular vs. plural, British vs American usages, etc.

Last but not least, I have a very strong reservation about the small sample size. The study uses only 172 documents for a bibliometric analysis, which is insufficient to draw robust conclusions, particularly given the complexity and breadth of the research area. Roger et al. (2020; doi:10.1007/s11192-020-03647-7) examined the impact of sample size on bibliometric reliability and found that variance stabilizes when the dataset exceeds 500 records. With only 172 documents, the dataset of this study likely fails to capture the full breadth of research in this field. The authors should either expand the dataset by refining the query strategy to include more relevant documents, or complement the bibliometric analysis with qualitative methods, such as content analysis of key publications.

Comments on the Quality of English Language

Nil

Author Response

Please see the attachment.

Author Response File: Author Response.docx

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1-   Line 10: The broad meaning of the word "WWTPs" should be written first.

2-   Line 12: It was reported that articles between 2000-2023 were scanned. It would be appropriate to write the scanned keywords.

3-   Line 12: Abbreviation for Web of Science is given in Line 78. It should have been given here first.

4-   Line 29: The phrase "nitrous oxide" is abbreviated as N2O. This shortening was already made in Line 9. Using only the abbreviation will be sufficient here.

5-   Word abbreviations should be made where they are first used. Please review the entire article.

6-   Pay attention to the capital letter rule at the beginning of sentences. For example Line 41...

7-   Line 69. The sentence starting with "This study..." should be given in a new paragraph.

8-   Line 130-144 ….etc. "Error! Reference source not found" The overall article should be checked.

9-   Line 163. The X axis of Figure 3 should be rearranged, and if necessary, a different style graphic should be added.

10- Line 202: The keywords and main idea of the articles should be checked.

11- Line 229. Instead of using the word "we", it would be more appropriate to use "this study" or something different.

Reviewer 2 Report

Comments and Suggestions for Authors

The study, The Impact of Bacteria on Nitrous Oxide Emission from Wastewater Treatment Plants: Bibliometric Analysis, described the impact of bacteria on N₂O emission from WWTPs during years using different software for bibliometric analysis and visualization.

I do not see how the statistical analysis of previously published works contributes to the science in the field and how is related to sustainability and sustainable development.

In conclusion, paper could not provide sufficient contribution to the research community and I do not recommend it for publication.

Comments on the Quality of English Language

 Minor editing of English language required.

Reviewer 3 Report

Comments and Suggestions for Authors

Introduction Section: It is recommended to include specific N₂O emission data in the introduction to enhance both the precision and readability of the content.

"Error! Reference source not found" Occurrences: Please resolve all instances of this error to ensure correct citation of references and data sources.

Page 9, Line 240: Upon the first mention of "ESDGs," please provide the full term to ensure clarity and understanding for the readers.

Page 7, Lines 193-194, Reference 25: The statement cited from Reference 25 appears unrelated to the main topic of the article. It is advised to remove this citation to maintain focus on the core argument.

Page 13, Lines 355-360: Relevant references should be cited to substantiate the data and conclusions presented in these lines.