Circular Economy in Wastewater Treatment Plants—Potential Opportunities for Biogenic Elements Recovery
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsSome specific comments on this manuscript are listed below:
General comment: The novelty of paper is limited. The methodology was not sufficiently described, with important information missing on the operational conditions used, the number of repetitions and the analysis. All data should be subjected to statistical analysis (e.g. error bars, standard deviation, etc.)
1. The introduction contains basic information. No new aspects were presented.
2. In the introduction, add recently published articles in this field (e.g. after line 123).
3. Introduction - briefly explain the motivation for undertaking this research, its relevance and originality, where it fits into the development of the field, and why it should be of interest to Water readers.
4. Introduction- The weaknesses and limitations of this study compared to other studies should be considered.
5. Line 137- 139 - Materials and Methods - Please add the geographical coordinates of the place where the research was conducted.
6. Point 2.2. Circulation of biogenic elements in the MWWTP (line from 176). Authors should provide information on measurement conditions and instruments/equipment (brand, society, city and country… etc.). Please add.
7. Results and Discussion - It is important to check that the writing text clearly expresses and explains each idea and result obtained.
8. Results- All data should be statistically analyzed and the error bar and standard deviation should be reported.
9. The discussion section of the article is poorly written. Must be upgraded with new articles. The description of the results and discussion is based mainly on comparing the values ​​of the obtained parameters with each other, without deeper explanations. This point should be expanded.
10. Please correct minor punctuation and lettering errors in the manuscript and check the entire article, e.g. remove the dot from the title.
11. The conclusions needs improvement - highlight the most important findings and identify the added value of the main finding.
12. Conclusions - consider adding numerical results to this section.
Author Response
Please see the attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsWATER 2023
Circular Economy in Wastewater Treatment Plant – Potential Opportunities for Biogenic Elements Recovery
Review Comments:
First impressions
- This work is original and important to the field of wastewater treatment and the circular economy.
- The authors have done a good job in telling a complex story involving wastewater treatment, nutrient recovery and the challenge of producing viable products (electricity and fertilizer).
- The structure and Technical English are good throughout the manuscript.
Abstract
- The abstract presents a good summary of the ideas and outcomes described in the manuscript.
Corrections: No corrections are needed in this part of the manuscript.
Introduction
- The authors have done a good job of stating the challenges wastewater treatment and how to incorporate this treatment into the circular economy.
- Both the quality of the science and the use of Technical English are good.
Corrections:
Page 2, line 73 – “Carbon sequestration through compost Composting” This is redundant. Did the authors mean “Carbon sequestration through sludge composting”?
Page 2, line 76 – “These micro-organisms sequester carbon in the soil through photosynthesis.” In addition to soil algae, a considerable amount of carbon is sequestered by the production of microbial biofilms within the soil. The biofilm is composed of polysaccharides, proteins and extracellular DNA. https://pubmed.ncbi.nlm.nih.gov/34999062/#:~:text=Soil%20carbon%20sequestration%20(SCS)%20refers,to%20store%20C%20in%20soils.
- Comment: Biochar could be produced from digester sludge to improve soil quality. https://www.sciencedirect.com/science/article/abs/pii/S0960852419315160
https://www.sciencedirect.com/science/article/pii/S0147651321009313#:~:text=The%20physicochemical%20properties%20of%20test,4.62%20g%C2%B7kg%E2%88%921.
- Biochar reduces the potential leaching of heavy metals into soils versus leaching from sewage sludge. https://link.springer.com/article/10.1007/s10163-015-0366-y#:~:text=The%20retention%20rate%20was%20defined,of%20Cr%20remained%20in%20biochar.
- In China there is a successful program that used cockroaches to consume all restaurant waste. The insects are harvested and turned into chicken feed. https://waster.com.au/china-using-cockroaches-for-food-waste/
- Even with SBRs, there are a number of recalcitrant compounds such as pharmaceuticals, PFAS and PAHs that due not break down and end up in the sludge or the effluent.
- Some WWTPs in the USA mix their digester sludge with manure from dairy farms. The mixture is composted for six months to allow for optimal breakdown and elimination of pathogens and is then sold as fertilizer.
Methodology
- The methodology section describes each of the treatment steps and methods in depth such that the experiments could be reproduced by another researcher.
- The authors have done a good job of describing their methodology.
Corrections: No corrections are needed in this part of the manuscript.
Comment: closed digesters - Digesters can significantly increase their methane production by disrupting the bacterial cells in the sludge by various means (thermal, ultrasound or mechanical grinding) before the sludge is added to the digester.
Results and Discussion
- The results and discussion sections are well written.
- The authors present a good case for the interpretations and conclusions based on the data generated from the MWWTP.
Figures and tables
- The figures and tables are easy to read and impart a good deal of information.
Corrections:
Page 7, line 267 – “High temperatures also hygienise the sludge and reduce the hydration” Change to “High temperatures also sterilize the sludge and reduce the water content”.
Comments/Suggestions for future experiments or analyses:
- There are no additional experiments or analyses needed for this manuscript. However, there are other question that could be addressed in future publications.
- Since this manuscript focuses on the circular economy and environmental sustainability, why is there no mention of the high level of N,P & C removal efficiency? The differences in values between stream 1 and 14 indicates a 90+% reduction in these values.
Conclusion
- The conclusions are in line with the data generated by the authors.
- There are no unjustified claims nor any need to tone down the conclusions.
- There are no redundancies between the text and the figures and tables.
Corrections: no corrections
References, tables and figures
- The citations are appropriate and accurate.
- The figures and tables need no corrections.
- Due to the complexity of the figures, there is a definite need for color in the figures.
Should this manuscript be published?
- This manuscript should be ready for publication once the authors have addressed the issues mentioned above.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsAll the queries have been adressed by the authors and all the comments have been satisfactorily adressed with supporting literature.
