Elucidating the Potential of Vertical Flow-Constructed Wetlands Vegetated with Different Wetland Plant Species for the Remediation of Chromium-Contaminated Water

Round 1

Reviewer 1 Report

The manuscript is original, interesting and in my view, it is a great contribution in the field of study. Since it presents a study on the elimination of Cr from wastewater by means of vertical wetlands, as an alternative to conventional systems with higher costs and energy consumption. The authors have evaluated different species to achieve Cr removal.

In my opinion, the manuscript is highly attractive to other readers and the proposed methodology is clear. The manuscript is well written. The methodology has been well conducted and the conclusions are clearly supported by the results.

I suggest this paper should be accepted but after minor revisions that can be seen below.

• In the methodology section, additional information is required on the flow rate treated in each wetland and the hydraulic residence time used.
• Can the species tested pose environmental problems as invasive species in other ecosystems? Additional information is required.

Author Response

Dear Editor,

Please see attachment

Author Response File: Author Response.docx

Reviewer 2 Report

        In this work, Bibi and the co-authors have systematically investigated the treatment of Cr by vertical flow CWs, the whole work and the obtained scientific results are well illustrated, I think it can be considered to be published on Sustainability after some comments are addressed.

1. Line 44, “the latter being 44 many fold toxic and mobile than Cr(III) [6] [7, 8].”, the English writing of this sentence should be revised and the references should be cited together.

2. Line 48-50, the cost of the adsorption is relatively low and almost without secondary pollution, you could refer to this reference (S. Bolisetty, M. Peydayesh, R. Mezzenga, Sustainable technologies for water purification from heavy metals: review and analysis, Chem. Soc. Rev. 48 (2019) 463–487. https://doi.org/10.1039/c8cs00493e.), I suggest to illustrate their disadvantages separately.

3. Line 55, the reason for the choose of vertical flow should be emphasized.

4. Line 79, the percentage should be weight, molar or volume?

5. Line 207, from the experimental section, the simulated wastewater is a Cr(VI) solution, but after 1 day treatment, its concentration could be reduced such greatly at alkaline surroundings?

6. Line 225, the contribution of Cr(VI) biosorption to the decrease of its concentration should be clarified.

7. Line 266, “any adverse effects” used here is not appropriate, the data in Table 2 also indicates some inhibiting effects although it’s not so apparent.

8. Figure 3 should be re-arranged and some labels are not large enough.

9. Line 376, why the Fe, Zn, Mn, Ca, K and Na content decreased significantly, if the reason could be ascribed to the preferential bio-adsorption of Cr(III) compare with these elementals, if the assumption is correct, if the element content order of these elements could be explained?

Author Response

Please see attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

1. The introduction should be widely elaborated. I think that authors should more express the general context of the indicated research issue.  What is the problem, what methods are applied to indicate the scale, what tools are applied, what forecast we can anticipate by current knowledge, how we can manage by risk limitation some isssues etc.? In the actual form the explanation is not enougth.
2. Verses 69-70 authors idnicate a wetland plant species, what is the justification for the followingspecies selection? Does the analysis require all of them or can some of them be omitted and application 
   of lower amount of different species could be enougth?
3. Authors said that experiment was conducted in April-September 2021? Is there any justification forsuch period of analysis indication?
4. Figure 2. I think that quality of the diagram should be improved. In my opinion the data without pictures(form of the chart is OK) is enough without pictures of plants, flasks etc. 
5. Authors elaborates the methods and tools which they have used for experiment, they should be elaborated in 1 paragraph where al
6. In verse authors said that smapling analysis were conducted at various intervals. Additonally authors said that experiment period was 30 days and in the first part of manuscript it was written that experiment was conductded in April-September, so what is the ultimate information
7. What justification of such intervals selection? I think  that if so many species wereapplied for experiment the periods of intervals should be shorter. However, if there is a justification ofsuch periods it is ok.
8. Methodology, how many times the measurements where repeated for each species, what was the difference between by statistical methods
9. Table 1  the following presentation is hard to read, I think thet data would be easier to understand in the form of chart in comparision that data for control sample (100%) and bar for each test (the figure 3 could be enough but the quality improvement is necessary).
10. Conclusions are too short. In this point authors should widely explain what they research bring additionally.In the following form conclusions are explanation just in form what were changes but the general context of  research is required.

Additionally there are some mistaktes in refences. In some of them authors bring information about volume and issue some titles of Journals were showed full and some are presented as abbreviated. Authors should unify this maybe with usage some refference manager software. All references should be elaborated in the same form without varieties.

Author Response

Please see attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

    The comments have been well answered and the article has been greatly polished, so I recommend to accept in the current form.