The Effects of Plants on Pollutant Removal, Clogging, and Bacterial Community Structure in Palm Mulch-Based Vertical Flow Constructed Wetlands

Round 1

Reviewer 1 Report

The manuscript presents routine work and the findings were not new, as it’s already broadly reported about the effects of plants in constructed wetlands. This paper provide an report based on 9 months field study, and in its present form does not bring new relevant information to the field.

Author Response

Dear reviewer,

thank you for your answer.

In our opinion this manuscript provides some interesting points in the field:

Research on mulch-based constructed wetlands. It is well known that constructed wetlands are environmentally friendly systems for wastewater treatment, but the substrate extraction and transport is the activity that exerts the highest environmental impact. Thus, the search for alternative substrates to gravel and sand must be encouraged. If the new substrates are obtained from local, renewable wastes, the sustainability of constructed wetlands becomes greatly improved. In the case of using forest wastes, the carbon balance of the constructed wetland can be positively changed.

Mulch, plants and clogging. To our knowledge, this is the first time the effect of plants on performance and clogging is described for mulch-based, vertical flow constructed wetlands working under real conditions. The resulting effect was not evident since the reactor with the plants performed worse than the reactor without plants during the first experimental period, until the one wihtout plants became clogged and things changed completely.

The results and experience obtained in this work have allowed us to refine the design of our constructed wetlands in terms of substrate selection, and construction with the goal to minimize the use of gravel and sand.

Reviewer 2 Report

This manuscript by Carrasco-Acosta et al. aims to assess the impacts of plants on the purification performance of constructed wetlands. The evolution of the fecal bacterial community is also investigated in parallel. The experiments have been soundly performed and the manuscript is correctly written even if several modifications appear suitable in order to improve this article. Hence, I recommend to accept this manuscript after major modifications. Specific comment are given below.

Abstract and Title “The effects of plants on the performance and bacterial community structure” needs to be modified. The meaning of performance needs to be clarify.

P1L37-38 “promising alternatives for the treatment of non-point source pollution” This sentence needs to be clarified, domestic wastewater are a point source pollution?

P1L38-39 “water to be treated” is not in the “basic composition of CWs. It does not make any sense, please correct.

P2L45-46 Is there any scientific reason for this exception? Is it reserved for French CWs?

P2L50-54 In this section could you furnish quantitative data on this assumption? For example what is the average sand weight for a classical CWs? In the same way, is the sand demand for the construction of CW significant in comparison to its use for concrete?

P2L55-59 And what? You should indicate here that in your study, the substrate will be palm tree mulch rather than sand.

In general in the whole manuscript you should be more precise when you speak about microbiological parameters. Indeed, you analyze fecal bacteria communities only (which is great).

P3L93-94 What is the mean HRT of wastewater in the seepage pit? You talk about primary settling, this information is therefore necessary.

P3L99-110 In this section you should be more precise on the water sampling? Is it flow-enslaved, time-enslaved? What is the sampled volume? These information are mandatory.

P3L114 “Water Analysis” what is it? A subtitle? Please correct

P5L208-222 What is the specific objective of this section? It seems to be only a repetition of the introduction. Hence it should be deleted, or merged within the introduction.

P6L227 The parameters of the influent were measured in the seepage pit or after pumping? It should be clearly stated.

Table 1 Why is the number of data variable between each parameter (26, 25, 9, 17)? Is there any logical reason beyond this fact?

P6L242-244 Here you have performed a statistical test and the result was “statistically different”. Hence, I don’t understand how you can write “their performance can be compared with confidence”? Please moderate your words.

P7L249 “o” please correct

Table 3: I don’t understand the aim to compare the whole removal parameters. Indeed, you notice slight and severe clogging on 1np, therefore the whole removal values are not compared for the same conditions. Please explain.

P7L258 “though” please correct

P7L257-265 The hypothesis presented in this section in unsatisfactory to explain the systematic negative removal values observed. Please correct, or furnish more convincing assumptions.

P7L269 Maybe I miss the information but you should explain what you consider as “statistical outlier”.

Figure 2 You should be consistent in the presentation of this figure, sometimes the line disrupted, sometimes not, please correct. I suggest to point out the clogging chronology on this figure.

P12L296-298 Here you consider that plants had only a physical contribution on the removal. It is speculative in my view. I don’t think that plants are present in CWs only to reduce the performance and be aesthetic! Please moderate this sentence.

P14L334-335 I cannot concur with this sentence. The removal is not better for 1p, it is better since 1np was clogged. Hence, based on your results, plants delay clogging but didn’t help achieving better removal.

3.4 In this section I don’t understand the distinction between light clogging and severe clogging. This clogging has only been observed on 1np? Why present your results like this?

P16L387-389 Is it the conclusion of your study? It needs to be tremendously enhanced and replaced in more general context! It is unacceptable to present such type of conclusion!

Author Response

Dear Reviewer,

Please find the answers in the file attached.

Thank you for your time and effort.

Your revision has been very helpfull.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors modifed the manuscript regarding reviewer's comments, and the manuscript have great improve.

Reviewer 2 Report

The authors have made significant efforts in order to follow my recommendations. As a result, i feel that the manuscript now deserves for publication in Sustainability.