Unsaturated Vertical Flow Constructed Wetland for Chlorothalonil Remediation with Target Application in Ethiopian Floriculture Industry

Round 1

Reviewer 1 Report (New Reviewer)

The manuscript entitled “Unsaturated vertical flow constructed wetland for chlorothalonil remediation with target application in Ethiopian floriculture industry" describes the performance of  UVF-CWs for chlorothalonil remediation. The article is well-written and minor revision is needed before this paper can be considered for the publication.

 

1.      In abstract, the removal efficiency percentage could be added.

2.      In Introduction, the selection of UVF-CWs over conventional wastewater treatment method needs to be explained.

3.      Authors need to compare the interaction parameter ANOVA analysis on chlorothalonil degradation.

4.      The schematic mechanism of chlorothalonil remediation needs to be explained.

5.      Cost-economic analysis and future of UVF-CWs for water reclamation must be stated.

Minor editing of English language required.

Author Response

We would like to thank you for your comments on our manuscript. We have worked towards improving the manuscript with your comments and suggestions in mind. Please find a detailed explanation of the changes made in response to the same. We hope that our revisions are satisfactory.

• The chlorothalonil removal efficiency was added in the abstract (Line 31).
• The selection ofUVF-CWs over conventional wastewater treatment method was elaborated on (Line 72-82).
• For the two factor repeated ANOVA analysis, further explanation was provided to add clarity to the text. The two independent variables used for the analysis of ΔpH, ΔDO, ΔEC and ΔT were C_in (influent chlorothalonil concentration) and saturation condition. For the interactive effect of the two independent variables in case of ΔpH further explanation was added (Line 319-331).
• A detailed schematic process of the water treatment have been explained in the experimental setup subsection (Line 164-167). Further detailed schematic diagram can be found in supplementary material 1.
• Cost-economic analysis of UVF-CWs for water reclamation were done in comparison with horizontal flow subsurface constructed wetlands, which have been used in previous literature for chlorothalonil remediation from water (Line 103-111). The future steps towards verification of long term effects of UFV-CW were touched upon in the conclusion section (Line 435-440).

Reviewer 2 Report (New Reviewer)

In the introduction, it should be noted whether this chlorothalonil is typically used in this type of crop or is something more regional. I know that it is used as a fungicide. Would this have any impact on the microbiota of the wetland system? Are chlorothalonil concentrations much higher than those found in real effluents? Justify the choice of these concentrations.

Table 1: Be careful with the presentation of the results, number of significant figures, and number of decimal places to indicate the uncertainty of the results. Include the sample no.

Bring more recent works (>2020) to discuss the results. Avoid citing references in conclusions.

Minor mistakes. language improval advised.

Author Response

We would like to thank you for your comments on our manuscript. We have worked towards improving the manuscript with your comments and suggestions in mind. Please find a detailed explanation of the changes made in response to the same. We hope that our revisions are satisfactory.

• Explanation was added to show how higher levels of chlorothalonil are used in floriculture industry as well as the large quantities of pesticide water which are sprayed on the plants. The accumulation of the chlorothalonil, over time, leads to higher concentrations of the pesticide in water runoff; which was why higher influent chlorothalonil concentration were used in this study (Line 149-155).
• In previous research, CWs treating chlorothalonil containing wastewater have shown presence of chlorothalonil degrading bacteria. Apart from this there has not been any impact on the microbiota which would lead to negative impact on the water quality of CW effluents. The explanation was added in the introduction section (Line 86).
• The values presented in Table 2 were checked and rectified in response to the comment about significant figures and errors (Line 301).
• Sample numbers were included in the Supplementary Materials 3, where all the chlorothalonil removal data has been recorded.
• More recent references (>2020) have been added to the discussion of the results (Reference # 20, 38, 41, 42, 43, 44, 46).
• References from the conclusion section have been removed.

Reviewer 3 Report (New Reviewer)

I think the manuscript fits for publiction with minor revision. 

Comments for author File: Comments.doc

Author Response

We would like to thank you for your comments on our manuscript. We have worked towards improving the manuscript with your comments and suggestions in mind. Please find a detailed explanation of the changes made in response to the same. We hope that our revisions are satisfactory.

• The substrate material, its geometrical sizes and analysis of metal oxides present in the substrate have been included as part of the materials (Subsection 2.1, Line 123-130).
• Further discussion about how the geometrical size and the presence of metal oxides in the substrate contributed towards higher chlorothalonil removal by adsorption was added (Line 383-389).
• Explanation about how a vertical flow structure under unsaturated conditions was beneficial as opposed to horizontal flow under partially saturated conditions was added (Line 389-391).

Reviewer 4 Report (New Reviewer)

The manuscript is well-organized and well-written. The study was also well-designed, and the conclusions are in line with the results. The paper addresses the optimization of operational conditions of CW used for pesticide remediation, specifically the HLR. I would like the authors to consider the following issues:

The authors have mentioned throughout the manuscript that previous studies have been conducted on the removal of chlorothalonil using constructed wetlands (CW), albeit under different operational and flow conditions, namely the HLR, the degree of bed saturation, and the number of stages. Therefore, in the Results and Discussion section, it is advisable for them to compare the removal of chlorothalonil with values presented in the literature. For example, they could create a table featuring the main operational conditions and corresponding removal efficiencies or calculate the Δ chlorothalonil concentrations, similar to what was done for the water parameters presented in Table 3.

Lines 100 and 118 please verify these citations.

Add error bars to the data shown in Figure 3.

Line 341, Please comment on the possibility of plants also contributing to the creation of microenvironmental conditions near their roots that enhance the adsorption or precipitation of pollutants. For instance, you can conduct a search in the literature.

Minor editing of English language required.

Author Response

We would like to thank you for your comments on our manuscript. We have worked towards improving the manuscript with your comments and suggestions in mind. Please find a detailed explanation of the changes made in response to the same. We hope that our revisions are satisfactory.

• The suggestion to add a table displaying a comparison of the operational parameters and chlorothalonil removal efficiency between our study and previous research works was implemented. The comparison can be found in Table 1 (Line 284).
• The two errors in the inline citations have been rectified.
• The error bars have already been added to Figure 3, however, they are not visible due to the scale of the plot. Although we tried to address this by using a logarithmic scale for the y-axis, we were not able to remedy this. The dataset with the error present has been included in the Supplementary Material 3.
• Further discussion about the importance of plant roots was included. The importance of plant roots to create habitable conditions for microorganisms as well as creating water channels through the substrate bed were addressed (Line 396-403).

Reviewer 5 Report (New Reviewer)

The manuscript was written well. It can be accepted after a minor revision. A few minor comments were given below:

Keywords should be in alphabetical order

Provide section and sub-section numbers

Line 100, there is "Error! 100 Reference source not found", please check this. 

Line 118, there is "Error! 100 Reference source not found", please check this. 

In the results and discussion, provide a table with key results and compare the improved efficiency with other research works (do not add this table in Supplementary Materials). It is necessary for readers to see the innovation and improved efficiency of the main manuscript. 

Avoid citation in conclusions, line 366 [14]

Remove citation number 37 in the references. 

 

Author Response

We would like to thank you for your comments on our manuscript. We have worked towards improving the manuscript with your comments and suggestions in mind. Please find a detailed explanation of the changes made in response to the same. We hope that our revisions are satisfactory.

• The keywords have been arranged in alphabetical order (Line 34).
• Section and sub-section numbers were added, which helped improve readability.
• The two errors in the inline citations have been rectified.
• The suggestion to add a table displaying a comparison of the operational parameters and chlorothalonil removal efficiency between our study and previous research works was implemented. The comparison can be found in Table 1 (Line 284).
• As per the reviewer’s suggestion, the citations from the conclusion section have been removed.
• The list of references has been updated and formatted uniformly.

Round 2

Reviewer 2 Report (New Reviewer)

The authors followed the recommendations made by the reviewer. The article has greatly improved in quality and is suitable for publication in its current form.

Reviewer 4 Report (New Reviewer)

The authors improved the manuscript and answered my questions. Their revisions are satisfactory.

Minor editing of English language required.

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

This study exhibits certain novelty and potential impact in the development of wetland technology for micropollutant removal. However, there are significant areas in the paper that require improvement. The writing needs to be significantly refined, and the scientific discussion needs to be strengthened. Additionally, the experimental design, operation, and data analysis lack clarity and fail to adequately support the study. For instance, the introduction focuses on the development of wetlands for chlorothalonil removal but also includes the study of a specific nozzle. However, the design, purpose, and knowledge gaps related to the nozzle's use are not introduced in the introduction section. The materials and methods lack sufficient detail, leading to unexplained data (e.g., control group) presented in the results section. Here are some specific comments to assist the author in improving the paper:

1. Does the journal require research highlights? If so, ensure that they adhere to the specified character limit.

2. In lines 58-71, the paragraph begins with chlorothalonil removal but then transitions into discussing the general treatment of pesticides. It is suggested to maintain a focus on the target compounds.

3. Materials and methods section:

a) Clarify how different types of media were utilized in the system.

b) Ensure consistency in terminology (e.g., pilot vs. mesocosms) and provide information on system size, sample collection frequency, and the rationale for multiple stages. Clarify if the reported removal efficiency represents overall removal efficiency and justify the use of two stages.

c) Specify the duration of each stage of operation. It is important to consider that wetland systems typically require several months to achieve stable conditions, which may impact the reliability of the results.

d) Thoroughly proofread the paper to address formatting errors, such as inconsistent units (e.g., L149) and other mistakes (e.g., L173, L286).

4. Table 1 and Figure 2 present repeated data.

5. Clarify the meaning of the control group in Table 2 and specify which HLR was used to obtain the data.

6. Improve clarity in Table 4 and reduce the number of significant figures. Ditto to other tables.

7. Address the issue of strange word size in L261.

8. Remove or provide relevant context for the discussion related to the nozzle, as it seems unrelated to the study.

9. Consider organizing the discussion into subsections and including more scientific aspects.

10. Note that co-authors are typically not listed in the acknowledgements, as is the case with theses/dissertations.

11. The format of references is really a mess. Moreover, the majority of the references are not up-to-dated, and many pesticide removal performances and removal pathways/mechanisms in CWs are not used to support the discussion of this paper.

Overall, it is highly recommended that authors could re-write the majority of this paper. It is also important to make the paper concise and clear with good logic, the current version of the paper is not friendly and contributes less to the research area.

 

Last but not least, I want to highlight that the aforementioned comments are just some examples, more drawbacks need to be sorted out before the re-submission.

see the general comments

Author Response

Reviewer 1:

 

We would like to thank you for your comments on our manuscript. We have worked towards improving the manuscript with your comments and suggestions in mind. Please find a detailed explanation of the changes made in response to the same. We hope that our revisions are satisfactory.

1. Upon crosschecking, we found that research highlights section is not included in the format described in the journal’s instructions. This section has now been removed from the manuscript.
2. The issue at line 65, where the paragraph starts with chlorothalonil removal but goes on to discuss generalised treatment to pesticides has been resolved. The sentence related to chlorothalonil has been removed while the discussion of technologies for pesticide removal has been kept. We felt this was important to highlight the advantages of constructed wetlands as compared to the described technologies for implementation in Ethiopia.
3. Materials and methods section:
   1. Clarifications were added about the influent preparation procedure in the methods section (line 153).
   2. Rectifications were made to maintain consistent terminology across the manuscript. The size of stage A and B tanks has been mentioned at line 106 in the materials section. Further details of the construction layout and size have been added in Supplementary Materials 5. Details of sample collection frequency and volume have been added (lines 164-183). The removal efficiency represents overall removal efficiency. A two-stage system was used to maximise the removal efficiency with low retention times under completely unsaturated conditions. This has now been explained at line 125.
   3. Details related to system stabilisation have been added (line 125-134). Time for testing of each condition has also been indicated at line 173.
   4. Formatting and grammatical errors have been addressed along with the consistency of all the units used.
4. Table 1 has been removed since it had repetition of data presented in figure 2.
5. Details of control group and HLR used have been added to the caption of Table 1 (previously Table 2, line 280).
6. Formatting of all the tables was rectified.
7. The issue of the strange word has been resolved. The text has been properly formatted (line 271).
8. New information related to use of spray nozzles in constructed wetlands has been added to the introduction part (lines 86-93). The use of spray nozzles allowed for a significant increase in the DO of the effluent water. Details of this can be found from lines 333-338.
9. Attempted to add more logical flow to the discussion section, getting rid of some points which could not be substantiated by the work done in this manuscript.
10. The issue of the Acknowledgements section has been rectified to remove the listed co-authors. Only the research supervisors were still mentioned in this section.
11. The references were updated as much as possible. Further efforts were taken to format them uniformly.
12. All the major changes including work on comments provided by other reviewers, has been highlighted in the revised manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript elucidated the efficacy of two-stage vertical flow CWs for chlorothalonil remediation in the pilot study. The results showed that the chlorothalonil could be effectively removed after flow through the CWs with relatively lower retention times. This manuscript has practical significance, as chlorothalonil is often used in floriculture farms and preferably near water bodies. CWs have been considered one of the cost-effective and natural-based solutions for chlorothalonil removal and agricultural wastewater purification that typically contains many nutrients. However, the current version of this manuscript should not be accepted due to the lack of necessary information about the experiment and results in this manuscript. There are several main points given below:

1.      There are some garbled characters for references in the paper, including lines 137, 286, and 298.

2.      In addition to the chlorothalonil concentration, the other water chemistry, including nutrient level, COD, pH, DO, TSS, EC, etc, in the pump station tank should be provided in the paper.

3.      The data in Table 4 is recommended to keep two decimal places.

4.      The results of substrate adsorption and uptake by plants for the removal of chlorothalonil in group 3 should be compared with those in the control systems. (page295-318)

5.      What is the thickness below the surface of the “top layer” in line 306?

6.      As an important parameter, the adsorption capacity of the substrate will inevitably affect the removal efficiency and the operating life of CWs. I did not find this value in the paper when the total of 74.6 Kg chlorothalonil would be removed until substrate saturation (line 311).  

 

Overall, I suggest authors to further double-check the content and complement the necessary data before resubmission.

The quality of the English language is generally good.

Author Response

Reviewer 2:

 

We would like to thank you for your comments on our manuscript. We have worked towards improving the manuscript with your comments and suggestions in mind. Please find a detailed explanation of the changes made in response to the same. We hope that our revisions are satisfactory.

1. The garbled references have been rectified. Formatting errors across the manuscript have been rectified.
2. The samples for water parameter analysis were collected from the tap outlet of stage B. Since stage A effluent samples were not analysed for water parameters, we are unable to provide this data in the manuscript.
3. Table 3 (previously Table 4) has been formatted to make the numbers legible. The rest of the tables were checked as well to ensure proper formatting.
4. Comparisons of all the results to control samples wherever applicable have been added (lines 256, 316-320).
5. The description of “top layer” has been rectified to add details (lines 316-320).
6. Since saturation of the substrate could not be achieved in the CW, we found it difficult to calculate the adsorption capacity of the CW.
7. All the major changes including work on comments provided by other reviewers, has been highlighted in the revised manuscript.
   
   

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript “Efficacy of a constructed wetland for chlorothalonil remediation from floricultural runoffs in Ethiopia”, by Stan Wehbe, Feleke Zewge, Yoshihiko Inagaki, Wolfram Sievert, N.T. Uday Kumar and Akshay Deshpande, presents information on the application of a constructed wetland for the removal of chlorothalonil from water. According to the authors, this is a pesticide that can end into water bodies due to its use in floriculture. The removal of the pesticide due to processes taking place in the wetland was measured.

The introduction is, in general, well-written. It provides enough information on the context of this manuscript and tells the most important aspects concerning the use of wetlands for the removal of pesticides.

In the section of Methods and Materials, the authors must include relevant information. There are parts of this section that require more details. As the authors know, there are some strategies to study treatments based in wetlands, therefore, it is essential to provide a careful description of the methodology. This allows, not only to facilitate the reproduction of the experiments (if a reader wants to do that), but also provides valuable information for the interpretation and discussion of results (and the context in which they were obtained).

The authors mentioned an “analysis of metal oxides” (lines 111 and 112), however, no information on the analytical technique was indicated. Moreover, the composition of the substrate is a result and should be presented in the section Results.

The authors wrote that the experimental setup was modified from a system used in a previous study (line 121). Are the authors sure that the (modified) experimental setup used for carbendazim in the earlier study does not affect the results in this study? The affectation of the plants, especially roots, the microbial community in the substrate and others could distort the results. The authors should discuss the validity of the results and present arguments supporting their idea that previous use of the experimental setup in the removal of another chemical compound does not affect the results in this study.

There are missing analytical details that must be completed.

The units should be presented following the rules of the International System. In certain parts appears the text: Reference source not found. Please check these details.

I have included some comments in the PDF document as well.

I consider that this paper can be published in Water after major revisions.

Comments for author File: Comments.pdf

Author Response

Reviewer 3:

We would like to thank you for your comments on our manuscript. We have worked towards improving the manuscript with your comments and suggestions in mind. Please find a detailed explanation of the changes made in response to the same. We hope that our revisions are satisfactory.

1. Details for all the materials and methods used have been added wherever they were previously lacking.
2. Details of steps taken to ensure the new results not being affected by previous work on the existing experimental setup have been added (lines 128-131).
3. The units have been rectified to comply with the rules of the International System.
4. Missing references have been rectified.
5. The detailed in-line comments provided in the separate pdf document have been addressed to the best of our abilities.
6. All the major changes including work on comments provided by other reviewers, has been highlighted in the revised manuscript.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The manuscript “Efficacy of a constructed wetland for chlorothalonil remediation from floricultural runoffs in Ethiopia”, by Stan Wehbe, Feleke Zewge, Yoshihiko Inagaki, Wolfram Sievert, N.T. Uday Kumar and Akshay Deshpande, presents information on applying a constructed wetland to remove chlorothalonil from water. According to the authors, this is a pesticide that can end into water bodies due to its use in floriculture. The removal of the pesticide due to processes taking place in the wetland was measured.

In an earlier revision, some corrections/revisions were requested. After reading the corrected version of the manuscript and the explanatory notes the authors included as a response, I believe that the manuscript is suitable for publication. Therefore, I consider that this paper can be published in Water without any further revisions.