Constructed Wetlands for Dairy and Livestock Wastewater Treatment: A Review
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis manuscript addresses an important topic for the treatment of dairy and livestock effluents in order to mitigate environmental impacts on the water-soil system. The manuscript offers information obtained from literature reviews on constructed wetland systems treating dairy and livestock effluents. The manuscript addresses thematic areas related to the scope of the journal Water, such as Water resources management, Water scarcity, and Water & wastewater treatment. Below are some suggestions and questions.
Suggestions
Title
The title expresses the themes addressed in the manuscript; therefore I have no suggestions for it.
Abstract
Suggestion to rewrite your Abstract with the following organization: insert an introduction that highlights the problem to be solved in a more summarized way. Then present the objective of your work. Complete this with a brief methodology. Add the main research results and finally present the main conclusion that answers your objective. Suggestion to make this adjustment respecting the 200-word limit for the Abstract.
Keywords
Do not use keywords that already exist in the title.
Introduction
It is suggested that you divide the introduction text into smaller paragraphs for each topic covered and link these paragraphs with connecting elements.
On line 48, adjust... As reported by [10]...
Suggestion to improve the wording of lines 109 and 110.
It is suggested that, before the objective of the work, a paragraph should be inserted outlining the need to gather important information for the dissemination of wetlands in the treatment of dairy and dairy farming effluents.
On line 111, I suggest removing the word "general".
Material and Methods
Divide the "Materials and Methods" section into at least two sub-sections and divide the text into smaller paragraphs. Include a description of the types of graphs used in your results and present the software, citation, and respective reference.
Results and Discussion
On line 158, adjust...3. Results and Discussions....
Divide large paragraphs into smaller paragraphs.
On line 256 adjustment...For instance, [42] reported....
On lines 257 and 258 adjustment...In contrast, [43] documented...
On line 259 adjustment...Similarly, [44] noted...
On line 261 adjustment... [45] reported....
On line 263 adjustment... reported by [42], was...
On line 266 adjustment...reported by [45] can be...
On lines 275 and 276 adjustment... For instance, [46] reported.....
On line 277 adjustment...values are from [4] and [42], with....
On lines 278 and 279 adjustment...were reported by [45,47], with...
On line 314 adjustment....107 tones....
On lines 322 and 323 adjustment...reported by [8]....
On line 325 adjustment...respectively, in [8] and [83]...
On lines 325 and 326 adjustment...[74] reported...
On line 327 adjustment...reported by [14] 140 mg/L...
On lines 328 and 329 adjustment...concentrated in [75] (SW) and significantly more diluted in [14] (pig urine and wash water)...
On line 333 adjustment...reported by [72] and [74], with concentration...
On line 336 adjustment...Nevertheless, [83] and [72] reported higher....
On line 365 adjustment...For example, [47] highlighted...
On line 368 adjustment...[49] carried out....
On line 370 adjustment...[43] submitted WW...
On line 372 adjustment...in a study conducted by [57], a filter....
On line 374 adjustment...conducted by [91], the treated...
On line 375 adjustment... [53] in a study...
Follow this correction pattern from here on.
Conclusions
The conclusion answers the objective of the work.
References
Adjust according to the Water journal's standards.
Adjust doi on line 824 of reference [14].
Adjust the wording of the following items: Funding, Data Availability Statement, Acknowledgments, and Conflicts of Interest.
Author Response
|
1. Summary |
|
||||||
|
Dear Editor and Reviewers, We would like to thank you for your useful suggestions and corrections. In order to taking into account comments provided by both reviewers, all the manuscript was reviewed, abstract was rewritten and paragraph n.2 was reorganized. Please find in the following the response (in red) to your comments. The corresponding revisions/corrections are highlighted in the re-submitted files.
Reviewer #1
|
|||||||
|
Comments 1: Suggestion to rewrite your Abstract with the following organization: insert an introduction that highlights the problem to be solved in a more summarized way. Then present the objective of your work. Complete this with a brief methodology. Add the main research results and finally present the main conclusion that answers your objective. Suggestion to make this adjustment respecting the 200-word limit for the Abstract.
|
|||||||
|
Response 1: Thank you for this comment. We change the abstract following your suggestion. “Dairy and livestock farms produce considerable amounts of wastewater, could pose an environmental risk if not properly treated and discharged. Conventional treatment plants can represent an inadequate and costly solution in terms of operation and maintenance, especially for small and medium-sized farms. Thus, a valid and sustainable alternative can be provided by constructed wetland (CW). This paper analyzed the use of CW systems at different scales to treat dairy wastewater (DWW) and livestock wastewater (LWW) all around the world in the last thirty years. This systematic review identified 50 case studies reported in 50 publications from 22 countries: 20 CW for LWW and 30 DWW. Per each type of WW the analysis reported and compared: CW layout, type of substrates, vegetations planted, design parameters, removal efficiencies for main chemical-physical parameters and management aspects. Gravel and sand are the most common substates used in CW to treat both type of WW. Regarding vegetation, Phragmites australis is the most commonly used species in CWs treating LWW, whereas Typha spp. are the most frequently used in CWs treating DWW. Hybrid-CW showed the highest removal performance for all the reported parameters. This review can improve knowledges on CW, offering a technical and practical overview on the status of CW for to treat LWW and DWW”. – Page 1, Abstract, lines 26-42.
|
|||||||
|
Comments 2: [Do not use keywords that already exist in the title.]
|
|||||||
|
Response 2: Thank you for this comment, the keywords have been modified following your suggestions and here are reported: Nature-based Solution; agricultural wastewater; removal efficiencies; substrates; vegetation; management aspects. Page 2, Keywords, lines 44-46.
Comments 3: [It is suggested that you divide the introduction text into smaller paragraphs for each topic covered and link these paragraphs with connecting elements.]
Response 3: Thank you for this comment. The introduction has been revised following your suggestions. In particular, the text has been divided into smaller and more thematically coherent paragraphs, and several linking sentences have been added to improve the logical flow and connectivity throughout the section. The following connecting elements were included to ensure smoother transitions between topics: - In this context, understanding the intrinsic characteristics of these effluents becomes essential for selecting appropriate treatment solutions. Page 2, 1 Introduction, lines 61-62. - This scenario highlights the need to evaluate existing treatment technologies and explore more efficient alternatives. Page 3, 1 Introduction, lines 79-80. - Despite these advantages, CW systems are not without limitations. Page 4, 1 Introduction, lines 126-127.
|
|||||||
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThis work presents a systematic review of the current applications of constructed wetlands for treating dairy and livestock wastewater, with a particular focus on pollutants, substrates, and vegetation.
Overall, the manuscript is information-rich and provides valuable insights for readers seeking an understanding of current contaminants originating from dairy and livestock farms, as well as the potential challenges of constructed wetland systems.
Therefore, I believe that it is suitable for publication after appropriate revisions. My specific comments are as follows:
(1) Line 82: The citation format of “[22,23] Steer et al., 2002)” is incorrect and should be revised.
(2) Line 234: The authors provide a detailed description of the water quality characteristics of DWW and LWW in Section 3.2. Are these characteristics representative of the influent directly entering the constructed wetland? Since pretreatment is discussed later in Section 3.3.1, it would be helpful to clarify the pretreatment transforms the complex influent into a state suitable for advanced treatment in the wetland. This clarification is important for understanding subsequent discussions on substrate and plant selection.
(3) Line 346: Before listing specific case studies in this section, the authors should summarize the commonly used pretreatment technologies, specifying which methods primarily remove TSS and which focus on reducing COD. Furthermore, is there a fundamental difference between these pretreatment processes and those used in conventional municipal wastewater treatment systems?
(4) Line 687: This section provides an overview of constructed wetland management. However, current version lacks a summary of key parameters, such as treatment capacity, hydraulic retention time, and treatment costs of typical constructed wetlands. Furthermore, how are operational stability issues caused by seasonal variations in temperature and rainfall addressed?
(5) Lines 739-742: The authors mention that gravel removes TP through adsorption. How is gravel that becomes saturated with phosphorus typically treated or regenerated? Could the treatment or regeneration process of gravel result in high maintenance costs or pose a risk of secondary pollution?
Author Response
Dear Editor and Reviewers,
We would like to thank you for your useful suggestions and corrections. In order to taking into account comments provided by both reviewers, all the manuscript was reviewed, abstract was rewritten and paragraph n.2 was reorganized. Please find in the following the response (in red) to your comments. The corresponding revisions/corrections are highlighted in the re-submitted files.
Reviewer #2
Comments 1: [Line 82: The citation format of “[22,23] Steer et al., 2002)” is incorrect and should be revised.]
Response 1: Thank you for pointing this out. Agree. We have, accordingly, made this correction.
Comments 2: [Line 234: The authors provide a detailed description of the water quality characteristics of DWW and LWW in Section 3.2. Are these characteristics representative of the influent directly entering the constructed wetland? Since pretreatment is discussed later in Section 3.3.1, it would be helpful to clarify the pretreatment transforms the complex influent into a state suitable for advanced treatment in the wetland. This clarification is important for understanding subsequent discussions on substrate and plant selection.]
Response 2: Thank you for pointing this out. Agree. We have added a few comments to emphasise this point.
“Yes, the wastewater characteristics reported refer to raw wastewater. For a better understanding, the term “raw” has been inserted in line 280. Therefore, the efficiencies reported refer to the entire system, including preliminary and/or primary treatments. The paragraph has been rewritten as follows: Table 2 and 3 show the characteristics of the raw water entering the entire treatment system. Therefore, the removal efficiencies reported refer to the overall system”. – Page 9, 3.2 Wastewater composition, lines 288-289.
Comments 3: [Line 346: Before listing specific case studies in this section, the authors should summarize the commonly used pretreatment technologies, specifying which methods primarily remove TSS and which focus on reducing COD. Furthermore, is there a fundamental difference between these pretreatment processes and those used in conventional municipal wastewater treatment systems?]
Response 3: Thank you for pointing this out. Agree. We have added a few comments to emphasise this point.
“As in conventional municipal wastewater treatment, these wastewaters undergo standard preliminary and primary operations. Preliminary treatment includes coarse screening, which removes large solids and provides an initial reduction of organic matter, and the use of degreasers, which reduce COD by capturing fat-rich fractions that would otherwise elevate the organic load of the influent. Primary treatment is performed through sedimentation, which significantly reduces TSS concentrations and, given the predominantly organic nature of these solids, also contributes to COD removal.
In this context, the implementation of appropriate pre-treatment steps becomes crucial for ensuring stable and efficient CW performance.” - Page 17, 3.3.1 Pre-treatment, line 401-410.
Comments 4: [Line 687: This section provides an overview of constructed wetland management. However, current version lacks a summary of key parameters, such as treatment capacity, hydraulic retention time, and treatment costs of typical constructed wetlands. Furthermore, how are operational stability issues caused by seasonal variations in temperature and rainfall addressed?]
Response 4: Thank you for pointing this out. Agree. We have added a few comments to emphasise this point. We did not perform an analysis of the costs and problems related to the operational stability of the systems in relation to variations in temperature and rainfall.
“In hybrid CWs treating DWW, the daily influent flow ranged from 0.1 to 15 m³·day⁻¹. The HRT reported varied between 3 and 14 days. Overall, COD removal efficiencies ranged from 62% to 99%, with a mean value of 82% (±12% SD). Case studies reporting COD removal efficiencies greater than 90% suggest that reliable system performance is typically achieved when the first treatment stage operates at an average HLR of 25–33 mm·day⁻¹. The daily flow rate of LWW treatment systems was approximately five times higher than that observed for DWW, ranging from 0.4 to 100 m³·day⁻¹. Consequently, HRT appears higher, showing values ranging from 4 to 29 days. COD removal efficiency varied from 26% to 94%, with a mean value of 73% (±21% SD). Case studies reporting removal efficiencies greater than 90% indicate that stable and effective treatment performance is achieved when the first stage units op-erate at an average HLR of 6–40 mm·day⁻¹”. - Page 27, 4 Main management aspects, lines 773-783.
Comments 5: [Lines 739-742: The authors mention that gravel removes TP through adsorption. How is gravel that becomes saturated with phosphorus typically treated or regenerated? Could the treatment or regeneration process of gravel result in high maintenance costs or pose a risk of secondary pollution?]
Response 5: Thank you for pointing this out. Agree. Iven if the main TP removal is to adoption (Pant et al. 2001) we decide to remove “adsorption” from the conclusion since the removal process of TP is not fully explained in the manuscript.
Page 28, 5 Conclusions, lines 818-819.
Response to Comments on the Quality of English Language
Response 1: In accordance to the comments provided by both reviewers, all the manuscript was reviewed and English improved.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsDear Editor,
The requested corrections have been made and the manuscript is accepted.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors have revised the manuscript in line with previous comments, and I have no further comments at this time.
