Wastewater Treatment Using Constructed Wetland: Current Trends and Future Potential

Round 1

Reviewer 1 Report

This paper reviewed the potential of wetlands in treating wastewater. I have several concerns regarding this paper. This topic is too wide and writing a review paper in this field is difficult. I can see many technical problems in whole the paper as a review paper. The authors missed many related and recent citations which made the quality of this review low. it is more like a chapter book, not a review paper. I can not see any novel findings in this review and my suggestion is rejection.

How this paper is in the scope of the processes journal? Can the authors justify? I think is more suitable for Environmental journals. 

The First 88 lines only have 10 references. This is a review paper and the authors should have more citations in the introduction. 

The statistics should be updated. Now is 2021 and the authors cited the statistics of the year 2012 in line 87. 

Lines 103-118: no references? why?

The copyright permission of all figures should be obtained. 

what is section 3: results? The review paper does have a results section. 

Again lines 178 to 201 no reference. This is not the style of academic paper writing.

The cited papers in Table 2 are old and not acceptable to make a conclusion for the future trend. 

In Table 5 there is only three cited paper? why the authors made a table? Same comment for Table 6.

Table 7 is meaningless for a review paper. 

Any conclusion for this review? 

 

 

 

 

 

Author Response

The authors would like to thank the reviewer for his valuable comments. Your comments have helped us to improve the paper. 

Author Response File: Author Response.docx

Reviewer 2 Report

COMMENTS

This is an interesting review paper and its subject fits the scope of the journal. However, several major issues affect the overall quality of this paper.

1. The innovation and the aim of the study should be added.
2. Lines 128-137: In my opinion the following text “In the literature, …., … become HFCWs” does not need and should be removed.
3. Figure 1. The caption of Figure 1 should be changed as follows: “Figure 1. Schematic layout of (a) free surface flow, (b) horizontal subsurface flow, and (c) vertical subsurface flow constructed wetlands”. Furthermore, the Figures 1b,c are not correct as they show water level above the substrate surface.
4. Line 161. Remove the subtitle “3.1.1. Subsubsection”
5. Lines 169-170: “The top layers (near the water surface) have high 167 oxygen concentration while the bottom layers have very low or zero oxygen concentration.”. It depends on the depth of water which should be added in the text. Also, add relevant reference.
6. Lines 197-198: Please add relevant reference.
7. Lines 223-224: Write down the reasons why this happens.
8. Lines 250-257: The following text “For a single-family, …., dimensions of 7.5m x 3.75 m.” concerns on-site systems and therefore, it should be a separate paragraph. Also compare and discuss these dimensions with those of the two relevant papers: (1) On-site treatment of domestic wastewater using a small-scale horizontal subsurface flow constructed wetland, Water Science and Technology, 62(3), pp. 603-614. (2) A small-size vertical flow constructed wetland for on-site treatment of household wastewater, Ecological Engineering, 44, pp. 337– 343. http://dx.doi.org/10.1016/j.ecoleng.2012.04.016.
9. Line 262: The thickness of the HDPE membrane used is usually 1.0 mm.
10. Lines 267-270: Please convert the inches in cm (SI units).
11. Figure 2: In my opinion, Figure 2 should be removed because it does not offer anything new.

12 Lines 414-415: Please add relevant references.

13 Table 3: A new column should be added with type of CW used in each case.

14. Lines 437-438: Please add relevant references.
15. Table 4: A new column should be added with type of porous media used in each CW system.
16. Table 5: A new column should be added with type of wastewater used in each CW system.
17. Subsection “4.6 Pharmaceuticals and Personal Care Products (PPCPs)”: A paragraph on the removal of endocrine disrupting chemicals (EDCs) from municipal wastewater using CW should be added based on the following relevant paper “Removal of Endocrine Disrupting Chemicals in HSF and VF Pilot-scale Constructed Wetlands. Chemical Engineering Journal, 294, pp. 146–156.”
18. Subsection “4.7 Agricultural wastewater”: Agricultural runoff also contain pesticides from point and non-point sources of pollution. A paragraph on the removal of pesticides using CWs should be added. The results of the following papers could be used: (a) Treatment of Agricultural Equipment Rinsing Water Containing a Fungicide in Pilot-scale Horizontal Subsurface Flow Constructed Wetlands. Ecological Engineering, 101, pp. 193-200. (b) Low-cost approaches for the removal of terbuthylazine from agricultural wastewater: Constructed wetlands and biopurification system. Chemical Engineering Journal, 335, pp. 647-656. (c) Fluopyram removal from agricultural equipment rinsing water using HSF pilot-scale constructed wetlands. Environmental Science and Pollution Research. DOI: https://doi.org/10.1007/s11356-021-15373-5
19. Line 581: Please add relevant references.
20. Lines 816-819: The following text “Some other …, … the wastewater [71]” should be moved to 4.7 subsection.
21. Lines 819-824: The following text “The removal …, … and the wetland type [72].” should be moved to 4.1 subsection, line 381.

 

Author Response

The authors would like to thank the reviewer for the constructive feedback and available comments. The implementation of the comments has resulted in considerable improvement of the manuscript. 

Author Response File: Author Response.docx

Reviewer 3 Report

1. The introduction needs a lot of references to support the statement. For example. line 80-81, line 84-86, and so on. The introduction must contain more bibliographic references taking account that the article is a review.
2.  In the section 2. "Wetland treatment systems" the authors don't describe the aerated treatment wetland. It is necessary to incorporate this king of wetland in a review. 
3. Section 3.3.1. It is not clear because mix CWs in general with specific design criteria to VF. It would be better to introduce different sub-section to each type of CWs.
4. The objetive of the figure 2  is not clear. It is difficult to understand the meaning of the figure. 
5. Appear a lot of bibliographic references in different format and these references are not in the section "references". For example line 223, line 227, line 395, line 439, line 442, line 466, line 487, line 490, line 492, line 518, line 740.
6. Section 4.8, use SSHF instead of HSSF as is established in the section 2.
7. Section 7.2. Line 758. Table 2?
8. In general, the article must include references in a lot os statements included, for example, line 197, lines 253-254, lines 419-423, lines 435-437; section 4.7, 4.8 and 4.9 need a lot of references, support table 8 with references, etc..

Author Response

The authors would like to thank the reviewer for his valuable comments. Your comments have helped us to improve the paper. 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors increased the quality of the paper during the first revision, however still needs some modifications.

Still, there are many recent review papers that are not considered by the authors such as https://doi.org/10.1016/j.eti.2021.101933, https://doi.org/10.1016/j.asej.2020.05.009, https://doi.org/10.1007/s11356-019-04300-4 , https://doi.org/10.1016/j.chemosphere.2021.131564, https://doi.org/10.1016/j.eti.2020.101261, https://doi.org/10.1016/j.ecoleng.2021.106318

Figure 1: you should insert each figure after the related text and not merged it together in a single Figure.   

In lines 542-553: the authors suddenly jumped to the removal of PPCPs using emergent plants. This pollutant is a type of persistent organic pollutants (POPs). I suggest allocating a separate section regarding the removal of POPs using different aquatic plants. 

Also, you can make one section regarding microplastics' existence in wetlands and how the plants act in this situation. Is there any removal or hindering plant growth rate? You may refer to https://doi.org/10.1016/j.jwpe.2021.101966

In the conclusion, also add the findings of how POPs and microplastics can be removed using CWs. and what is the future trend of studies in terms of pollution remediation in CWs.

Author Response

All the comments have been addressed as per the reviewer's recommendations. 

Author Response File: Author Response.docx

Reviewer 2 Report

Most of my comments have been successfully addressed and the manuscript has been greatly improved. 

Author Response

Thank you for your constructive comments and great suggestions. 

Author Response File: Author Response.docx

Reviewer 3 Report

The authors have improved the paper. However, they still need to improve some sections:

1. Section 2. Wetland treatment systems. The information about the aerated constructed wetland is confused. The authors establish the OTR (Oxygen Transfer Rate) in g/m2-d but this terms is measured as mg O2/L h. This statement needs further explanation.
2. Section 2.3.1. The design criteria should be more specific. For example, the Organic Loading Rate, Hydraulic Retention Time, etc. This kind of parameters are the main design parameters. 
3. This review has to include a future trend in this topic to talk about constructed wetland microbial fuel cell.
4. In general. Include actual references to support the statements. 

 

Author Response

The manuscript has been updated according to the comments and suggestions given by the reviewer. 

Author Response File: Author Response.docx

Round 3

Reviewer 1 Report

The paper is improved while still needs changes as follow: 

 

Reference 20 should be replaced by https://doi.org/10.1007/s11356-019-04300-4

Section of microplastic is poorly written. The authors explained only the existence of microplastic in CWs. We need to see fate too. You should show the studies which contributed to the removal of microplastics in wetlands such as https://doi.org/10.1016/j.scitotenv.2020.137785, https://doi.org/10.1016/j.jhazmat.2021.125615, https://doi.org/10.1016/j.cej.2021.132752 , and many more.

This paper https://doi.org/10.1016/j.eti.2021.101933 should be cited in line 384 where you explained phosphorous removal. 

Figure 4 has a missing word in the box on the right side. Geo-

Conclusion: for the removal of POPS and microplastic you should add some range that has been removed in the different CWs. 

Why did you add MFC in the conclusion suddenly? 

 

Author Response

Please find attached our responses to the respected reviewer's comments. 

Author Response File: Author Response.docx