Influence of Water Salinity on the Efficiency of Fe0-Based Systems for Water Treatment
, Hans Ruppert 5 and Chicgoua Noubactep 1,6,7,8,*
Round 1
Reviewer 1 Report
I recommend publication of this manuscript as it has been presented well with sufficient data to support the conclusions.
English language quality is adequate and the manuscript is easy to read and understand
Author Response
Many thanks for this evaluation.
Sincerely,
Dr. Noubactep
Reviewer 2 Report
Comment 1
There are no pH values reported in this study, aside from the pH of tap water (initial pH = 8.3). The corrosion of ZVI and the production of FeCPs affect the solution pH, which will then affect the removal of the contaminant dyes.
Comment 2
The water quality parameters of the tap water should be reported in addition to the pH (8.3). Parameters such as total hardness and alkalinity (bicarbonate) may affect the production of FeCPs.
Comment 3
Was the final concentration of chloride measured in any of the experiments?
Comment 4
Was the concentration of Fe (total iron = Fe2+ and Fe3+) measured in any of the experiments? The concentration of Fe may help explain the E values (removal of dye contaminants) in terms of the level of FeCPs present in solution which affected the removal of dye contaminants.
Comment 5
The concentration of MB is reported as 10 g/L in the captions for Figure 1 and Figure 5. The concentration of MB should be 10 mg/L not 10 g/L.
Comment 6
In Figure 5b, why is there no difference between the tap water and salt water for ZVI4?
Comment 7
There were four dyes used in this study to observe the behavior of ZVI as function of chloride affecting different dyes. Some description of the dyes has to be provided such as the different properties of the dye molecules affecting their removal by ZVI. Properties such as water solubility and molecular weight should be reported.
Comment 8
The best overall performance was observed for ZVI2. In Table 1, the iron content of ZVI2 was reported to be 90%; what is the content of the other 10% of ZVI2? The non-Fe content difference between ZVI 2 (90% Fe) and ZVI4 (~100% Fe) may be related as to why ZVI2 performed better.
Comment 9
Why was ZVI1 selected as the ZVI for experiments in Figures 1,2,3,4 (instead of ZVI2)?
Comment 10
In the ABSTRACT, replace wastewaters with waters or with contaminated waters (line 20).
Comment 11
According to the results shown in Figures 2, 3 and 4, the SW (40 g/L NaCl) system clearly removed less MB (and OM) than the TW system after 46 days and earlier. Therefore, the word “delayed” should be replaced with “decreased” in the ABSTRACT (line 34) and elsewhere in the manuscript.
Comment 12
Line 94, Equation (1): The corrosion of ZVI (Fe0) in water typically produces hydroxide (OH-) which increases the pH. Equation (1) may be written as:
Fe0 + 2H2O <=> Fe2+ + H2 + 2OH-
Author Response
Comment 1
There are no pH values reported in this study, aside from the pH of tap water (initial pH = 8.3). The corrosion of ZVI and the production of FeCPs affect the solution pH, which will then affect the removal of the contaminant dyes.
We fully agree with the Reviewer, it was a mistake not to monitor the pH value. The iron concentratiion was equalily not determined. These values would have significantly improuved the discussion. Previous works showed no significance changes oft he pH values. It is better not to address these both aspects (Fe concentration and pH value). We will consider that in further works.
Comment 2
The water quality parameters of the tap water should be reported in addition to the pH (8.3). Parameters such as total hardness and alkalinity (bicarbonate) may affect the production of FeCPs.
The Cl– concentration of water was given. The full analysis in now given.
The average composition of this water is (mg L−1): Cl−: 9.7; NO3−: 7.7; SO42−: 30.0; HCO3−: 88.5; Na+: 6.0; K+: 0.5; Mg2+: 7.3; Ca2+: 32.6, and its initial pH was 8.3.
Comment 3
Was the final concentration of chloride measured in any of the experiments?
No, it is really not necessary.
Comment 4
Was the concentration of Fe (total iron = Fe2+ and Fe3+) measured in any of the experiments? The concentration of Fe may help explain the E values (removal of dye contaminants) in terms of the level of FeCPs present in solution which affected the removal of dye contaminants.
The Reviewer is completly right! The Fe concentration would have improved the discussion.
Comment 5
The concentration of MB is reported as 10 g/L in the captions for Figure 1 and Figure 5. The concentration of MB should be 10 mg/L not 10 g/L.
Many thanks, it is corrected!
Comment 6
In Figure 5b, why is there no difference between the tap water and salt water for ZVI4?
ZVI4 is the least reactive material. The observation means that NaCl could not impact its corrosion.
Comment 7
There were four dyes used in this study to observe the behavior of ZVI as function of chloride affecting different dyes. Some description of the dyes has to be provided such as the different properties of the dye molecules affecting their removal by ZVI. Properties such as water solubility and molecular weight should be reported.
Many thanks, a table (Table 1) was added within Material and Methods.
Table 1: Physico-chemical characteristics of the dyes
Comment 8
The best overall performance was observed for ZVI2. In Table 1, the iron content of ZVI2 was reported to be 90%; what is the content of the other 10% of ZVI2? The non-Fe content difference between ZVI 2 (90% Fe) and ZVI4 (~100% Fe) may be related as to why ZVI2 performed better.
The Reviewer is right. However this discussion is over the scope of this work. Birke et al. (2014) have presented an excellent discussion and Li et al. (2019) gave a complete review. Typically, tt is impossible to correlate efficiency and Fe content.
Comment 9
Why was ZVI1 selected as the ZVI for experiments in Figures 1,2,3,4 (instead of ZVI2)?
Why should ZVI2 be selected? ZVI1 is the material we have tested the most (our operational reference). ZVI1 is also the most used material for field implementation in Europe.
Comment 10
In the ABSTRACT, replace wastewaters with waters or with contaminated waters (line 20).
Done, Thanks! Its now read polluted waters.
Comment 11
According to the results shown in Figures 2, 3 and 4, the SW (40 g/L NaCl) system clearly removed less MB (and OM) than the TW system after 46 days and earlier. Therefore, the word “delayed” should be replaced with “decreased” in the ABSTRACT (line 34) and elsewhere in the manuscript.
Generally, NaCl accelerates contaminant removal. It is in this context that "delay" is preferred to "decrease". Both "delay" and "decrease" are used but not randomly interchanged.
Comment 12
Line 94, Equation (1): The corrosion of ZVI (Fe0) in water typically produces hydroxide (OH–) which increases the pH. Equation (1) may be written as:
Fe0 + 2H2O <=> Fe2+ + H2 + 2OH-
The reviewer is right. We have just preferred writing with the consumption of H+ (equally the increases pH value) which is the oxidant of Fe0.
Reviewer 3 Report
Dear authors,
first of all thanks for your contribution.
Metallic iron (Fe0) is a reactive material to treat saline wastewater, this paper provide a study of quiescent batch experiments were performed to characterize the effect of chloride (Cl–) ions on the efficiency of methylene blue (MB) discoloration in the presence of Fe0. Cl– was used in the form of NaCl at concentrations ranging from 0 to 40 g L–1.
At the end of the introductory paragraph, I suggest you better highlight the scientific novelty of your study. Even if the purpose of the study is well explained, it is important to highlight what the additional/new contribution to the research is. It would be useful, as well as interesting, to insert at least one introductory paragraph dealing with the efforts made by research not only closely linked to one's own type of study but in general. Then you could continue with a paragraph dealing with studies much more similar to yours in order to provide a general - detailed view. In particular, it would be interesting to offer an insight into the practical applications of the problem addressed in this document.
Salinity causes problems not only on the sewage system but also on the treatment plant (the heart of the plant, the biological unit in the presence of chlorides is unable to treat the liquid thus causing unpurified discharges on receiving water bodies and therefore consequent problems environmental). Fast times of interception of the sources of contamination allow a rapid containment and less damage. For this reason there are studies that address this problem; here are some bibliographic suggestions.
doi: 10.1016/j.watres.2010.09.024
https: doi: 10.3390/w13070934
In conclusion, I believe the document includes solid content, but some aspects need to be improved, by improving them this manuscript can have its value and impact.
I hope these recommendations are helpful to the authors and wish the best of luck in the further review process.
Author Response
Metallic iron (Fe0) is a reactive material to treat saline wastewater, this paper provide a study of quiescent batch experiments were performed to characterize the effect of chloride (Cl–) ions on the efficiency of methylene blue (MB) discoloration in the presence of Fe0. Cl– was used in the form of NaCl at concentrations ranging from 0 to 40 g L–1.
Many thanks for this evaluation!
At the end of the introductory paragraph, I suggest you better highlight the scientific novelty of your study. Even if the purpose of the study is well explained, it is important to highlight what the additional/new contribution to the research is. It would be useful, as well as interesting, to insert at least one introductory paragraph dealing with the efforts made by research not only closely linked to one's own type of study but in general. Then you could continue with a paragraph dealing with studies much more similar to yours in order to provide a general - detailed view. In particular, it would be interesting to offer an insight into the practical applications of the problem addressed in this document.
Many thanks for these remarks, we have rather broaden the context in the intitial phase oft he introduction. This ist o remain focused on NaCl. We have then mentioned other anions in the outlook.
Salinity causes problems not only on the sewage system but also on the treatment plant (the heart of the plant, the biological unit in the presence of chlorides is unable to treat the liquid thus causing unpurified discharges on receiving water bodies and therefore consequent problems environmental). Fast times of interception of the sources of contamination allow a rapid containment and less damage. For this reason there are studies that address this problem; here are some bibliographic suggestions.
Suggestion 1: doi: 10.1016/j.watres.2010.09.024
Passerat J., Ouattara N.K., Mouchel J.-M., Rocher V., Servais P. (2011): Impact of an intense combined sewer overflow event on the microbiological water quality of the Seine River. Water Res. 45, 893–903.
Suggestion 2: https: doi: 10.3390/w13070934
Sambito M., Freni G. (2021): Strategies for improving optimal positioning of quality sensors in urban drainage systems for non-conservative contaminants. Water 13, 934.
Considered, thanks! Very interesting indeed, one pillar of our research in rainwater harvesting and city design. These 2 papers are very helpful.
In conclusion, I believe the document includes solid content, but some aspects need to be improved, by improving them this manuscript can have its value and impact.
I hope these recommendations are helpful to the authors and wish the best of luck in the further review process.
Thanks!
Round 2
Reviewer 2 Report
N/A
Reviewer 3 Report
Dear Authors,
the requested changes have been made. In my opinion, now, the paper is ready for publication.
