Wastewater Treatment in Central Asia: Treatment Alternatives for Safe Water Reuse

Round 1

Reviewer 1 Report

The title of the manuscript reads Wastewater treatment in Central Asia: Treatment alternatives for safe water reuse and was submitted to be published in the special issue: Cutting-edge Technologies for Wastewater Treatment Management and Environmental Protection. However, the work presented does not reflect the latest technologies available and used in this field. There were several mentions of technologies used in Central Asia for wastewater treatment, but these could not be considered as cutting-edge as such, and did not really suggest tangible solutions for the issue of inadequate wastewater treatment facilities in this region, as announced in the abstract. Furthermore, this manuscript does not add knowledge or substance to the existing literature in the field. More work should be put in for the overall improvement of the manuscript to address the shortcomings listed above.

Author Response

We appreciate this reviewer’s thoughtful comments and feel that our review actually does reflect the state of the science for wastewater treatment technologies, while also considering current economic and practical limitations in Central Asia. The field of practical wastewater treatment, which started in response to manage effects to water quality worldwide, is a slowly evolving discipline. Application of cutting-edge wastewater treatment technologies depends on successful and repeated testing of scientific advances in design of more efficient bioreactors, lower cost filtration, advanced oxidation, and use of synthetic nanomaterials. In our review, we provide examples of past and current wastewater treatment technologies used in Central Asia, briefly discuss issues with incomplete and inadequate treatment leading to contamination of surface and groundwater (this aspect will be covered more thoroughly in a separate article) , with a focus on health risk caused by reuse of wastewater in agricultural production, aggravated  by water scarcity this region faces, seeking to raise awareness on societal, governmental and regulatory bodies in Central Asia. There is thus a critical need to improve wastewater treatment in Central Asia to reduce health risks. Accordingly, we discuss treatment system compartments, and present promising alternatives from the literature. To our knowledge, there are no other reviews of this scope and scale focusing on Central Asia available. To help emphasize the contributions of this review, we have added a short section entitled “Future Perspectives at the end with our predictions of the most appropriate technologies to be considered by system operators, regulators, and ministries as they continue to make infrastructure improvements.       

 

Reviewer 2 Report

This paper provides a comprehensive overview of the research area and sets the stage for the study. it would be better to provide a brief explanation or definition when introducing abbreviations such as CECs, PCBs, and CAST.

 

 

Author Response

We thank Reviewer #2 by the suggestions given. The paper was thoroughly revised and, where appropriate, explanations or definitions were inserted when introducing abbreviations (lines 44-54 and 137-142). New references were also inserted to guide the reader for complimentary information.

Reviewer 3 Report

After reviewing the article and for a greater impact on readers, it would be important to address the following comments:

 

1) The authors only present tables and illustrations in sections 3.3, 3.4, and 3.5. It would be good if this information is also included in the other sections of the manuscript.

2) In the case of section 2, it would be interesting to present a Table where the different methods used are compared; for example volume of water treated per year for each method.

3) In the tables presented in section 3, it would also be good to describe from which region the samples of the water to be treated were taken.

The review manuscript is focused on analyzing alternative water treatments that come from polluted water in Central Asia, particularly from the regions of Kazakhstan, Uzbekistan, Kyrgyzstan, Tajikistan, and Turkmenistan.

Although the manuscript analyzes the different conventional and unconventional methods most used for this purpose, it would be important for the authors to include in sections 2 and part of 3, tables and figures that illustrate and demonstrate the usefulness and effectiveness of the methods shown in these sections. For example, it would be good to illustrate the volumes that are used in purification as well as the different contaminants that have been found, and the quality of the water that is obtained and its use, either for human consumption or for the agricultural sector as described.

Author Response

Following the suggestions of Reviewer #2, we made changes to address each comment raised. In section 2, new figures/illustrations (Figures 1-4) were included in the revised version of the manuscript, as well as a new Table (Table 2) with a comparison summary of the most used wastewater treatment technologies in Central Asia, including typical treated wastewater volumes for each method, and complimentary texts (lines 157-159, 160-161, 227-228, 245-247, 274, 276, 318-319, 322-324 and 365-367). In section 3 the manuscript is focused on analyzing alternative water treatments that can be applied to treat wastewaters in Central Asia, being prepared to present technical solutions according to literature published in different countries around the world. Accordingly, Tables in section 3 do not give focus on the region from where samples of water to be treated were taken, rather preferring summarizing the removal of several targeted contaminants of emerging concern by alternative treatment technologies. Related to the volumes that are used in purification, cross flows were reported in new Table 4 for each reference (whenever the parameter value was reported), since cross flow is the typical parameter mentioned in the studies dealing with membranes technology.

Reviewer 4 Report

1)    Line 30; adsorption, advanced oxidation processes, and managed/unmanaged

2)    The number of keywords is high and should be reduced.

3)    Line 337; An economic analysis utilizing the rate of return (ROR) method indicated that biochar presents itself as a cost-effective, eco-friendly, versatile, and high-capacity adsorbent alternative to activated carbon for CECS (Contaminants of Emerging Concern) removal (https://doi.org/10.1007/s11356-018-3327-x)

4) The inclusion of cost-effectiveness and economic analysis sections is vital in this context.

5)    Risk assessment for water reuse in Central Asia should be also added.

6)    Future perspectives should be separated from the conclusion. What needs to be done in future research? This question should be answered in this section. Also, the limitations of current research are not clear.

Minor editing of the English language is required.

Author Response

We appreciate the specific comments by the Reviewer and made changes to address each comment. We have fixed the punctuation error (line 30), reduced the keywords (lines 33-34), included the new reference (line 419), and added information that cost-effectiveness is critical for newer technologies adoption in developing countries (lines 417-419 and 483-484). We have added a separate section entitled “Risk assessment” (lines 56-69 and 692-700), as well as many new references and texts to guide the reader for complimentary information (lines 435-437). Finally, our Conclusions section was revised and renamed “Future Perspectives” which includes a discussion of the recommended resource and technology assessment, limitations of this review, and implementation of new technologies. 

Round 2

Reviewer 1 Report

Thanks for making those changes to the manuscript. They have improved the quality of the work and therefore better convey the solutions to the local challenges listed. 

Reviewer 4 Report

I have carefully checked the responses and modifications of the revised manuscript and found that the authors have properly modified their manuscript according to the Reviewers' comments. Hence, I think that it is now acceptable for publication.

Minor editing of the English language is required