Performance Assessment of Natural Wastewater Treatment Plants by Multivariate Statistical Models: A Case Study
, Sayeda M. Abdo 2, Anyi Hu 3, Mohamed Azab El-Liethy 4, Mohamed S. Hellal 5, Hala S. Doma 5 and Gamila H. Ali 2
Round 1
Reviewer 1 Report
The paper, entitled Performance Assessment of Natural Wastewater Treatment Plants in Upper and Lower Egypt by Multivariate Statistical Model, is a scholarly work and can increase knowledge on this domain. The authors provide an interesting and original study, the content is relevant to Sustainability. The abstract and keywords are meaningful. The manuscript is quite well written and well related to existing literature.
I have some specific and general comments:
- About the collection of samples of wastewater, is there only one collection and storage of the samples, or is there a campaign of collection? In this case, what about the potential variability of samples?
- is there any storage of the samples? if yes, what are the conditions?
- how many samples were collected? is there any replication for each analysis?
- please check title of subsection 2.4 "algal" instead of "agal"
- Please define Detention time in Table 1.
- About Nutrients removal (lines 312 to 317), please discuss this point and detail what are the similar technologies, thus compare them in term of efficiency and maybe in termes of costs, limitations and gains.
Author Response
Response to Reviewer 1 Comments
The paper, entitled Performance Assessment of Natural Wastewater Treatment Plants in Upper and Lower Egypt by Multivariate Statistical Model, is a scholarly work and can increase knowledge on this domain. The authors provide an interesting and original study, the content is relevant to Sustainability. The abstract and keywords are meaningful. The manuscript is quite well written and well related to existing literature.
We are thankful to the reviewer for providing valuable comments and suggestions for improvement the manuscript.
Comments and Suggestions for Authors:
Point 1: - About the collection of samples of wastewater, is there only one collection and storage of the samples, or is there a campaign of collection? In this case, what about the potential variability of samples?
Response 1: Samples of each discipline (i.e., physicochemical parameters, parasitology, algae, bacteriology) were collected in separate bottles.
Point 2: is there any storage of the samples? if yes, what are the conditions?
Response 2: Yes, Thanks, I wrote it in the material and methods section line 133.
Point 3: How many samples were collected? is there any replication for each analysis?
Response 3: Sixty-four samples were collected during the study. Triplicate samples were collected from each stage of each WSP. So, the total number of the samples with their replicate were 192.
Point 4: please check title of subsection 2.4 "algal" instead of "agal"
Response 4: Thanks, the spelling mistake has been corrected.
Point 5: Please define Detention time in Table 1.
Response 5: The available detention times were defined in table 1.
Point 6: About Nutrients removal (lines 312 to 317), please discuss this point and detail what are the similar technologies, thus compare them in term of efficiency and maybe in termes of costs, limitations and gains.
Response 6: Some details about nutrients removal have been added accordingly.
Reviewer 2 Report
1) Line 53, 54 and part of 55, the other factor is poverty.
2) Line 104 to 105, check for grammatical mistake. Also, for lines 105 to 106, lines 106 to 107, line 113 to 115,
3) The sentence classifying Egypt as upper and lower Egypt (line 116) is ambiguous and misleading. Use conventional means to re-name the two areas.
4) For Lines 150 to 163: include a map of Egypt, showing the upper and lower areas. Then, a fully blown map of the study area, clearly showing some of the key attributes of interest and the sampling points.
5) In line 153 to 154, it is not clear why the three protozoa pathogens were selected.
6) Under Table 1 for each of the WSP, include characteristics of key influent parameters. A detailed description of the influent characteristics is also necessary.
7) With a Detention Period ranging between 3 and 46 days, one wonders how the differences in variability associated with treatment system design and layout were filtered out.
8) Tracer tests are not expensive and could have been used to identify the percentage of dead zone in all the ponds. Treatment is a function of the percentage of dead zones and therefore, a key component is such studies.
Author Response
Response to Reviewer 2 Comments
We are thankful to the reviewer for providing valuable comments and suggestions for improvement. We have thoroughly revised the manuscript and addressed the questions below in the revised manuscript.
Comments and Suggestions for Authors:
Point 1: Line 53, 54 and part of 55, the other factor is poverty.
Response 1: The sentence has been rephrased.
Point 2: Line 104 to 105, check for grammatical mistake. Also, for lines 105 to 106, lines 106 to 107, line 113 to 115.
Response 2: The sentences have been rephrased accordingly.
Point 3: The sentence classifying Egypt as upper and lower Egypt (line 116) is ambiguous and misleading. Use conventional means to re-name the two areas.
Response 3: This classification is a historical classification and relatively based on demographic and health surveys (DHS).
Point 4: For Lines 150 to 163: include a map of Egypt, showing the upper and lower areas. Then, a fully blown map of the study area, clearly showing some of the key attributes of interest and the sampling points.
Response 4: The map (Fig. S1) showing the sampling points in the Egyptian governorates has been corrected.
Point 5: In line 153 to 154, it is not clear why the three protozoa pathogens were selected.
Response 5: Those three protozoa pathogens are the most common worldwide and in Egypt. Also, Cryptosporidium oocysts are highly resistant to hard environmental conditions and disinfectants [1]. Therefore, evaluation the removal of these pathogens in the WWTPs is necessary.
Point 6: Under Table 1 for each of the WSP, include characteristics of key influent parameters. A detailed description of the influent characteristics is also necessary.
Response 6: A detailed description of the influent characteristics and other treatment stages were shown in the supplementary figures S3-S10. Because there are several figures for the characteristics of wastewater in different stages, we put them in the supplementary material.
Point 7: With a Detention Period ranging between 3 and 46 days, one wonders how the differences in variability associated with treatment system design and layout were filtered out.
Response 7: Overall, the results proved that the effluents of WSPs with HRT < 11 days did not conform to the Egyptian legalizations. However, the WSPs with long HRT showed good results.
Point 8: Tracer tests are not expensive and could have been used to identify the percentage of dead zone in all the ponds. Treatment is a function of the percentage of dead zones and therefore, a key component is such studies.
Response 8: I totally agree with you that the calculation is dead zones is important for our study. So, we highlighted this limitation in the discussion part line 658.
References
- WHO Guidelines for Drinking-water Quality. World Health 2011, 1, 104–108, doi:10.1016/S1462-0758(00)00006-6.
Reviewer 3 Report
The authors have presented an interesting topic on the water treatment process based on WSP and analysed it statistically.
The overall presentation is very good. My only suggestion is to relate these findings from a global point of view. For example, how these findings from Egypt, can be beneficial to a reader who is in a different country. Since the journal platform is international, it is better to link problems and potential for different other countries, with respect to these results. This linking could be done in the Introduction and Conclusions.
Author Response
Response to Reviewer 3 Comments
Comments and Suggestions for Authors
The authors have presented an interesting topic on the water treatment process based on WSP and analyzed it statistically. The overall presentation is very good. My only suggestion is to relate these findings from a global point of view. For example, how these findings from Egypt, can be beneficial to a reader who is in a different country. Since the journal platform is international, it is better to link problems and potential for different other countries, with respect to these results. This linking could be done in the Introduction and Conclusions.
We sincerely thank the reviewer for the positive response. The revision has been made accordingly.
Reviewer 4 Report
1. My first impressions on this work
Congratulations to this working team (7 authors)
This is a very complete environmental work,
a) it involves a huge experimental work and effort on environmental characterization
b) it involves a multi-disciplinary team for chemical-biochemical and environmental characterization
c) and includes bio-statistics and other statistical tools to help in conclusions
---------------
2. My suggestions
2.1 in section "2.2. Physicochemical characterization"
improve text...
e.g.
a) total phosphorus -> total phosphorus (TP)
b) ...close reflux dichromate method (5210-D) -> reference to SMEWW (Standard Methods For the Examination of Water and Wastewater)
c) ...HANNA block digester and spectrophotometer. (please specify more)
d) ...sample filtration using GF/C paper method (2540-D) (help needed)
e) ...carried out according to international standard methods (APHA, 2017) (is this a reference?)
2.2 in section "2.5. Statistical analysis"
When I started reading this section I was convinced that it was made a PCA analysis...
Then I so that, in fact, the subject was Non-metric multidimensional scaling
Can you improve this?
2.3 in Figure 1
a) I have some problems to visualize data above 80% information recovery... (you have a total of 67.8%)
> is it preferable/possible to see a 3D scree plot?
b) in figure replace "total Kjeldahl nitrogen" by TKN?
c) in figure replace "total phosphorus" by TP?
2.4 Please, be coherent in assumed nomenclature...
in ln. 177 dbRDA was defined
"Distance-based redundancy analysis (dbRDA)"
in ln. 240 was used as db-RDA
2.5 Attempting to all experimental work (errors and estimated uncertainties) I have difficulties in accepting percentage values (e.g. variations) to the second decimal place...
Is it meaningful keeping the second decimal?
I think these results should be rounded always to the first decimal...
2.6 in Table 2...
a) replace "t" by "TV" (test value)
b) present TV values rounded to the second decimal
c) replace "P" by "p-value"
d) usually p-values have 3 decimal places (if keeping 4... please format all numbers to same decimals)
2.7 in Table 3...
a) replace "t" by "TV" (test value)
b) replace "P" by "p-value"
------------
3. Question
In section "3. Results" I have difficulties with your comment...
"The PCA vectors indicated that the pollution indicators (BOD, COD, TKN) were mainly associated with the lower Egypt WSPs"
From Figure 1 I have difficulties in accepting this comment...
Author Response
Response to Reviewer 4 Comments
Comments and Suggestions for Authors
- My first impressions on this work
Congratulations to this working team (7 authors)
This is a very complete environmental work,
- a) it involves a huge experimental work and effort on environmental characterization
- b) it involves a multi-disciplinary team for chemical-biochemical and environmental characterization
- c) and includes bio-statistics and other statistical tools to help in conclusions
We sincerely thank the reviewer for the insightful suggestions. Detailed revisions were made as suggested below.
Point 1: 2.1 in section "2.2. Physicochemical characterization"
improve text...
e.g.
- a) total phosphorus -> total phosphorus (TP)
- b) ...close reflux dichromate method (5210-D) -> reference to SMEWW (Standard Methods For the Examination of Water and Wastewater)
- c) ...HANNA block digester and spectrophotometer. (please specify more)
- d) ...sample filtration using GF/C paper method (2540-D) (help needed)
- e) ...carried out according to international standard methods (APHA, 2017) (is this a reference?)
Response 1: This part has been rephrased accordingly.
Point 2: 2.2 in section "2.5. Statistical analysis"
When I started reading this section, I was convinced that it was made a PCA analysis...
Then I so that, in fact, the subject was Non-metric multidimensional scaling
Can you improve this?
Response 2: The principal component analysis (PCA) based on the Euclidean distance was employed to characterize the patterns of physicochemical parameters in WSPs (Fig. 1). While the non-metric multidimensional scaling (nMDS) analysis based on the Bray–Curtis distance index was used to map bacterial indicators in WSPs across the treatment stages (Fig. S11).
Point 3: 2.3 in Figure 1
- a) I have some problems to visualize data above 80% information recovery... (you have a total of 67.8%)
> is it preferable/possible to see a 3D scree plot?
- b) in figure replace "total Kjeldahl nitrogen" by TKN?
- c) in figure replace "total phosphorus" by TP?
Response 3: The 3D plot has been provided, and all corrections have been made. Thanks
Point 4: 2.4 Please, be coherent in assumed nomenclature...
in ln. 177 dbRDA was defined
"Distance-based redundancy analysis (dbRDA)"
in ln. 240 was used as db-RDA
Response 5: The corrections have been made accordingly.
Point 6: 2.5 Attempting to all experimental work (errors and estimated uncertainties) I have difficulties in accepting percentage values (e.g. variations) to the second decimal place...
Is it meaningful keeping the second decimal?
I think these results should be rounded always to the first decimal...
Response 6: The changes have been made thoroughly.
Point 7: 2.6 in Table 2...
- replace "t" by "TV" (test value)
Response a: “t” is the statistic t similar to R value, It is produced by the program.
- present TV values rounded to the second decimal
Response b: the numbers in the tables have been unified.
- c) replace "P" by "p-value"
Response c: "P" has been replaced by "p-value"
- d) usually p-values have 3 decimal places (if keeping 4... please format all numbers to same decimals)
Response d: the numbers in the tables have been unified.
Point 8: 2.7 in Table 3...
- replace "t" by "TV" (test value)
Response a: “t” is the statistic t similar to R value, It is produced by the program.
- replace "P" by "p-value"
Response b: "P" has been replaced by "p-value"
Point 9: 3. Question
In section "3. Results" I have difficulties with your comment...
"The PCA vectors indicated that the pollution indicators (BOD, COD, TKN) were mainly associated with the lower Egypt WSPs"
From Figure 1 I have difficulties in accepting this comment...
Response 8: Thanks, you are right. This sentence has been deleted.
