Integrated Bioreactor and Wetland-Based Approaches for Agricultural Drainage Treatment: A Comprehensive Review of Design, Performance, and Field Applications

Response to Reviewer 1 Comment

1. Summary

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files. We appreciate the reviewer’s constructive comments, which have helped improve the manuscript's clarity and scientific rigor.

2. Questions for General Evaluation

Reviewer’s Evaluation

Response and Revisions

Does the introduction provide sufficient background and include all relevant references?

Yes

We have reviewed and updated the introduction to include additional references on bioreactors and wetlands to better contextualize the study.

Are all the cited references relevant to the research?

Yes

All references have been verified to ensure relevance to the manuscript.

Is the research design appropriate?

Yes

The methodology has been clarified, and a detailed explanation of the literature search and inclusion/exclusion criteria has been added.

Are the methods adequately described?

Can be improved

We revised the Methods section to explicitly mention logical connectors, the total number of articles retrieved, inclusion/exclusion criteria, and systematic review considerations.

Are the results clearly presented?

Yes

Results are clearly described in the text and summarized in Table 1.

Are the conclusions supported by the results?

Yes

The conclusions reflect the findings presented in the manuscript.

3. Point-by-point response to Comments and Suggestions for Authors

Comments 1: The logical connectors used in the keyword search (e.g., AND, OR, NOT) are not reported.

Response 1: Thank you for pointing this out. We have added information on the use of logical connectors in keyword searches to the Methods section.

"Keywords were combined using logical operators (AND, OR) to ensure a comprehensive search."

Comments 2: The total number of articles initially retrieved is not specified, nor are the objective inclusion and exclusion criteria.

Response 2: Agree. We have included the total number of articles retrieved and detailed the inclusion/exclusion criteria.

Comments 3: A systematic review protocol, such as PRISMA, was not adopted.

Response 3: Agree. We have clarified that a systematic approach inspired by PRISMA principles was applied to enhance transparency and reproducibility.

Comments 4: The comparative Table 1 lacks essential information, such as operational conditions.

Response 4: We have updated Table 1 to include operational conditions, advantages, and limitations of each substrate (Table 1).

Comments 5: The decomposition of organic matter is mentioned without considering that this process strongly depends on the characteristics of the medium.

Response 5: Agree. We have added a paragraph in Section 3.2 to explain how substrate properties such as porosity, particle size, carbon composition, and biodegradability influence microbial activity and organic matter breakdown.

Comments 6: Information related to the geometry of the bioreactors (dimensions, configuration, and arrangement) is not provided.

Response 6: Agree. We have added detailed information on reactor geometry, configuration, and arrangement in Section 3.1.

Comments 7: Information related to the geometry of the bioreactors (dimensions, configuration, and arrangement) is not provided, although it is relevant for comparison among the described systems.

Response 7: We thank the reviewer for this important comment. We agree that geometric information, including dimensions, configuration, and arrangement, is relevant for comparing bioreactor performance

Where detailed geometric information was not reported in the original studies, we have explicitly noted this limitation in the text to ensure transparency and help readers interpret reported treatment efficiencies.

4. Response to Comments on the Quality of English Language

Point 1:

Response 1:   All English language usage has been carefully revised to ensure clarity, precision, and compliance with MDPI style.

5. Additional clarifications

No further clarifications are required at this stage. All reviewer comments have been addressed.

Response to Reviewer X Comments

1. Summary

hank you very much for taking the time to review this manuscript. We sincerely appreciate the reviewer’s constructive comments and positive evaluation regarding the structure and classification of the literature. Please find the detailed responses below. The corresponding revisions and corrections have been highlighted in track changes in the resubmitted files.

2. Questions for General Evaluation

Reviewer’s Evaluation

Response and Revisions

Does the introduction provide sufficient background and include all relevant references?

Can be improved. The Introduction has been revised to include additional foundational reviews and monographs in the field.

Are all the cited references relevant to the research?

Yes (improved). The reference list has been expanded to include patent literature and additional review papers relevant to bioreactors and constructed wetlands.

Is the research design appropriate?

Yes. As this is a review article, the structure and classification approach remain appropriate and unchanged.

Are the methods adequately described?

Not applicable (review article).

Are the results clearly presented?

Can be improved. Additional illustrative figures (Figures 1–X) have been added to enhance clarity.

Are the conclusions supported by the results?

Yes. The conclusions remain supported by the synthesized literature.

3. Point-by-point response to Comments and Suggestions for Authors

Comments 1: The authors present an interesting review that summarizes and analyzes data on bioreactors and natural or artificial wetlands for reducing pollutant loads in agricultural drainage systems. The review's main strength is its clear structuring, classification, and discussion of the available information from scientific articles. However, in Section 2, the authors limit the sources of scientific information used in articles, which, in my opinion, is inappropriate. For such technical areas, it is important to consider data cited in patents. The review should be supplemented with patent data; after searching using google. Patents, epo.org, SciFinder, and other resources will significantly expand the modest list of 46 titles.

Response 1: Thank you for this valuable suggestion. We agree that patent literature is an important source of technical innovation in applied environmental engineering.

Accordingly, Section 2 has been revised to incorporate relevant patent data identified through searches in Google Patents, the European Patent Office (EPO), and SciFinder.

The reference list has been expanded beyond the initial 46 publications to include selected patents describing innovative reactor configurations, flow control mechanisms, and system optimization strategies.

These additions strengthen the applied and technological perspective of the review.

Comments 2: Furthermore, the review urgently needs illustrative material to make the material quicker and easier to understand, and clearly demonstrate the achievements. Five to seven figures from the most authoritative articles discussed should be selected and cited in the review. In the introduction, I would also recommend including a figure dedicated to the pollutants under consideration—listing them, their emission ranges or concentrations, and related details—to confirm the severity of the problem.

Response 2: We appreciate this important comment and agree that visual materials significantly enhance clarity and readability.

In response:

• A new Figure 1 has been added to the Introduction, illustrating the main pollutants in agricultural drainage systems, including their typical concentration ranges and environmental impacts.
• Additional schematic figures (Figures 2–6) have been incorporated to clearly present:
• Bioreactor classifications (in-line, off-line, subsurface),
• Natural versus constructed wetlands,

These figures enhance the manuscript's pedagogical clarity and support the classification framework presented in the review.

4. Response to Comments on the Quality of English Language

Point 1: Minor grammatical and stylistic issues.

Response 1:   The manuscript has been carefully revised to improve clarity, grammar, and scientific style. All modifications have been highlighted in track changes.

5. Additional clarifications

We would like to emphasize that the revisions have significantly strengthened the manuscript by:

• Expanding the reference list to include patent literature.
• Adding multiple schematic and conceptual figures to enhance clarity.

We sincerely thank the reviewer for the constructive comments, which have greatly improved the quality and completeness of our work.

Response to Reviewer 3 Comments

1. Summary

Thank you very much for taking the time to review this manuscript. We sincerely appreciate the reviewer’s constructive and encouraging feedback. The comments helped us improve the scientific depth, clarity, and relevance of the review.
Below, we provide detailed point-by-point responses. All corresponding revisions and corrections are highlighted in the revised manuscript.

2. Questions for General Evaluation

Reviewer’s Evaluation

Response and Revisions

Does the introduction provide sufficient background and include all relevant references?

Yes

[Please give your response if necessary. Or you can also give your corresponding response in the point-by-point response letter. The same as below]

Are all the cited references relevant to the research?

Yes

Is the research design appropriate?

Yes

Are the methods adequately described?

Yes

Are the results clearly preseted?

Yes

Are the conclusions supported by the results?

Yes

3. Point-by-point response to Comments and Suggestions for Authors

Comment 1: The manuscript is based on a current literature base, which is a significant advantage of the work. However, to enhance the substantive value of the work, it would be beneficial to increase the number of references.

Response 1: Thank you for this suggestion. We agree that expanding the reference base strengthens the manuscript's scholarly value. Therefore, we have added recent, high-impact references to support key sections, including bioreactor performance, wetland efficiency, field-scale applications, and emerging contaminants.

Comments 2: The main advantage of the article is the presentation of bioreactors and wetlands within a single framework.

Response 2: We appreciate this positive feedback. To reinforce this key contribution, we further emphasized the integrated bioreactor–wetland framework across the Introduction, Future Perspectives and Recommendations, and Conclusion. The comparative discussion was refined to improve coherence, readability, and scientific clarity.

Comments 3: It would be desirable to more clearly emphasize field applications, not just laboratory-scale studies.

Response 3: We agree with this important recommendation. Accordingly, we expanded the Field Applications and Case Studies section to highlight real-world implementations, including large-scale agricultural drainage systems in North America and Mediterranean regions. Performance variability linked to climate, hydraulic retention time, and influent nitrate concentration is now discussed.

Comments 4: Because the review is more descriptive, it would be good to consider a more critical approach to the analysis of available materials.

Response 4: We agree and have strengthened the review's critical analytical dimension. The revised manuscript now discusses system limitations, performance variability, uncertainties, and contradictory findings across studies in the Current Limitations and Research Gaps and Future Perspectives sections.

Comments 5: It would be helpful to clearly indicate conflicting results in the literature and discuss performance variability across systems and environmental conditions.

Response 5: Thank you for this valuable suggestion. We added a dedicated discussion of variability and conflicting findings, addressing differences due to design configuration, climate, influent composition, and seasonal conditions. This enhances the manuscript’s analytical depth and scientific rigor.

Comment 6: In the Materials and Methods section, it would be helpful to indicate which references were selected as the main ones for assessing the topic.

Response 6: We agree. The Materials and Methods section was revised to clarify selection criteria, emphasizing key foundational and highly cited studies used to structure the review and evaluate treatment performance.

Comment 7:The manuscript contains very similar content (Abstract vs Introduction; Introduction vs Conclusion). It would be good to describe these topics differently.

Response 7:
We acknowledge this point and revised the manuscript to reduce redundancy.

• The Abstract now focuses on concise outcomes and impact.
• The Introduction emphasizes scientific context and research rationale.
• The Conclusion highlights synthesis, implications, and future directions.

Comment 8: It would be good to add a conceptual drawing illustrating the integration of bioreactors and wetlands.

Response 8:We appreciate this suggestion. A conceptual figure illustrating the integrated bioreactor–wetland treatment framework has been added to improve visualization, clarity, and reader engagement.

4. Response to Comments on the Quality of English Language

Point 1:

Response 1:

The manuscript has been thoroughly edited to improve grammar, clarity, coherence, and scientific tone. Repetitive wording was reduced, and technical terminology was standardized throughout the text.

5. Additional clarifications

We believe the revised manuscript now offers stronger critical insight, clearer field relevance, and a more robust integrated framework. We sincerely thank Reviewer 3 for their thoughtful and constructive feedback, which significantly improved the quality of this work.