Trihalomethane Formation Potential at the Barekese Water Treatment Plant and the Related Cancer Risk to Consumers in the Kumasi Metropolis of Ghana

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript deals with a very important and interesting issue (DBPs). in many developing countries this isuue is ignored and consequently their effects on the human life is still ambiguos.

Authores did a very interesting projects but some improvements need to be addressed.

- there are manny editing errors (pages numbering, lines numbering, typo errors)

- there is no citation for figure 1 through the test

- please provide the WTP, Chlorine dose and contact time in the section of materials and methods (Barekese WTP layout and processes)

- in the sampling section, the authores mentioned that they collected samples from the final treated water which is not the case (in results they mentioned the different points of collection)

- what type of samples do you collect? Grab or composite?

- in section 3.1 you refer to table 3.1, the correct is table 2

- in section 3.2 you refer to figure 1, the correct is figure 3

- please correct hte nomenculture of table 3 and 4

- Unfortunatley I can't listing you the typo errors due to the lack of line numbering.

 

Comments on the Quality of English Language

- some language mistakes are present

Author Response

The authors have responded to all the reviewer comments.

Please see the attached file.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The title is long and confusing and it is preferable to shorten it

The abstract is very long, part of it is an introduction with references which is not acceptable in the abstract, thus. It needs to be shortened

Page 3 Section 1.1 is recommended to be sent for section 2 (material and methods)

Page 4 section 2.2 the written paragraph is somewhat confusing and needs to be rephrased in the form of clearer and shorter points to facilitate understanding of the unit referred to.

Page 5 section 2.4 It is recommended to rephrase this section in shortened points with subtitles for each analysis, also merged with section 1.1

Page 9 Figure 3 Redrawing is recommended with colorized lines and separating the legends, and equations out beside the graph to decrease the confusing

Author Response

The authors have responded to all the comments and suggestion raised by the second reviewer.

Please see the attached detailed responses and the evidence location in the manuscript.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

In this manuscript, the authors used the of measurements of COD as a surrogate of DOC, temperature, pH, chlorine residual and chlorination contact time to determine the THMs formation potential in the treated water at the Barekese WTP. The correlations between THMs formation potential and Water Quality Parameter were monitored, after them the human health risk value for males and females by using determined THMs were calculated (lifetime average daily dose, lifestage integrative cancer risk).

The article is current, original, at a good professional level. I appreciate the topic itself and the chosen procedure of the solved issue, literature search (list of references), conclusions and recommendations. The disadvantage of the article is the low number of samples taken (a total of 36 samples were collected in the first week of January 2023), evaluating the measured data using linear regression with 5 to 6 values ​​is very imprecise, which can also be seen from the constant R2 (fig. 1)

I have some question and comments:

1. Why was January 2023 selected for sampling, would it be necessary to do this monitoring of DOC and THMs in other seasons of the year.

2. Portions of the filtered water samples were sent to the Water Quality Laboratory…, why? How was the filtration done? THMs are already volatile at room temperature, the question is whether there was a loss of THMs before the analysis?

3. How were THMs determined? Was it direct injection into the gas chromatograph, or was a headspace, sorption or extraction method used to isolate THM from water? Were individual components analyzed (TCM, DBCM, DCBM and TBM) or the sum of THMs?

4. Table 1 - Eigenvalues, what does F1 to F5 mean?

5. I quote from the text: “The head of works is situated about 1 kilometer south of the abstraction point and at an elevation of x meters”. Can you correct (complete) it?

6. When an aluminum-based coagulant is used, it would also need to be monitored in the treated water, what are its values ​​in the treated water?

7. Was the contact time of chlorine with the treated water monitored, what was the dose of chlorine at the entrance to the contact tank (water reservoir?) and at the exit?

8. Determination of Trihalomethane Formation Potential (THMFP) was calculated by equation 3. It does not work for me that the result is mg/l because Ct is the disinfection contact time in hours.

9. In surface waters, in addition to COD, the BOD value is often monitored, their ratio determines whether it is a biodegradable substance or not. Or absorbance, alkalinity and turbidity. These values ​​are missing from the article. Which parameters were included in the Principal Component Analysis (PCA)? Only those mentioned in the article?

10. Specific ultraviolet absorbance (SUVA) provides a general characterization of the nature of natural organic matter (NOM) in a water sample and is typically performed for the purpose of determining disinfection by-product (DBP) formation potential. SUVA is calculated by dividing the UV absorbance at 254 nm (cm-1) by the DOC, dissolved organic carbon, (mg/L) of a water sample. A high SUVA indicates a large portion of humic matter present in the water and that NOM will control coagulant dose. Since aromatic organics have a greater tendency to react with disinfectants to create DBPs, a high SUVA indicates there is a greater potential for the formation of DBP’s. Could you add the SUVA parameter to the article?

11. The DOC parameter should be better described, each surface water may contain other organic pollution, e.g. the content of humic substances (ratio of humic acid and fulvic acid), low-molecular aromatic substances are not removed from the water by coagulation, these are then precursors to the formation of DBPs.

12. What are the recommended doses (concentrations) or limit values ​​for chlorine, TOC or DOC in Ghana? Residual chlorine is very high (1,9-2,6 mg/l), it would be necessary to reduce it, which would also reduce THMs formation.

13. Why 5 to 6 values ​​were used in the results and linear regression calculation. It would be necessary to confirm this with further measurements.

Author Response

The authors have responded to all the comments and suggestion raised by the third reviewer.

Please see the attached detailed responses and the evidence location in the manuscript.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have addressed all the concerns, manuscript is suitable for publication.