Mild Fenton Processes for the Removal of Preservatives: Interfering Effect of Methylisothiazolinone (MIT) on Paraben Degradation
Round 1
Reviewer 1 Report
The authors undertook the Mild Fenton processes for the removal of preservatives: Intefering effect of methylisothiazolinone (MIT) on parabens degradation. The manuscript lacks the novelty and poor presentation. I did not find any thing new in this manuscript. Fenton chemistry is well-known process for the degradation.
1. I did not find any novelty of the study, please discuss and incorporate.
2. Authors need to incorporate data of different amount of H202.
3. Authors should incorporate different amount of paraben.
4. Why authors choose paraben for degradation?
5. How to remove Fe from the solution after reaction?
6. Authors should add degradation in dark.
7. Why authors perform up to pH 5? Authors should include different pH condition including neutral pH.
Author Response
Reviewer #1:
The authors undertook the Mild Fenton processes for the removal of preservatives: Interfering effect of methylisothiazolinone (MIT) on parabens degradation. The manuscript lacks the novelty and poor presentation. I did not find anything new in this manuscript. Fenton chemistry is well-known process for the degradation.
The authors would like to thank the reviewers for their helpful and constructive comments and the editor for giving us the opportunity to improve the quality of the manuscript. Responses are indicated in blue in the following paragraphs and corresponding changes in the new version of the manuscript are highlighted in yellow. The whole manuscript has been reviewed in order to improve both the content and the quality of it. There are new paragraphs in every section of the manuscript.
- I did not find any novelty of the study, please discuss and incorporate.
After reviewing the manuscript, we agree that the novelty of this study was not very well highlighted. The novelty of the manuscript is that we are simultaneously treating different parabens (five) and we have added their most common substitute, which is methylisothiazolinone. We have studied the possible results of treating them together, which is what happens in real life. As far as we know, in previous studies they have always been treated separately, so this would be the first study in which they are mixed.
In addition, it has been reported in the literature that sometimes contaminants can act as iron complexes (as is the case), which makes the importance of treating the mixture of different families of contaminants even greater.
We have inserted new paragraphs in the introduction, stating this fact and explaining that sometimes contaminants can act as iron complexing agents, modifying the system. (lines 82-87 and 92-94). Two supporting citations have been added to this paragraph (references 22 and 23).
- Authors need to incorporate data of different amount of H20
Following the reviewer's suggestion, a new series of experiments were performed using half the amount of hydrogen peroxide that was used in the original manuscript. This amount was selected because in the original experiments approximately half of the peroxide was consumed, and we wanted to know if reducing the amount would have a significant impact on the degradation of the pollutants. These data are reflected in Figure 7 and their discussion appears in a new paragraph on the lines (406-421) . In the materials and methods section, 2 lines have also been added (lines 138-139).
- Authors should incorporate different amount of paraben.
As the reviewer comments, the variation in concentration of model contaminants may be of interest in this type of research. We chose a concentration value low enough to allow adequate solubility of the contaminants, since the solubility of some compounds is relatively low, but high enough to allow us to follow them by analytical methods and to allow us to calculate kinetic constants. We found it interesting to work at the actual concentration conditions, which could be addressed in future work, but the main objective of this work was to study interferences, and at such low dilutions this effect would have been very dilute and more difficult to appreciate.
- Why authors choose paraben for degradation?
Concern regarding parabens has been growing in recent years because they have been shown to have a toxic effect as an endocrine disruptor. Legislation in both the United States and Europe has focused on regulating their use, banning some, and controlling their presence in environmental systems. In the introduction a new paragraph has been added on the lines (35-41 and 50-53) in which this importance is more clearly indicated than in the first version of the manuscript. Two new citations have been added to support these statements (references 3 and 4).
- How to remove Fe from the solution after reaction?
As the reviewer suggests the separation of catalysts after use can be important, especially in heterogeneous systems. In our case, we are working with dissolved iron at concentrations of 5 mg/L, which is a value within the water discharge limits of many European Union countries, including the authors' home country, Spain. In the case of Spain, the limit is 10 mg/L, so adding a separation stage is not mandatory and is not so relevant in this case.
- Authors should add degradation in dark.
The dark experiments were performed in all cases and were labeled as Fenton to differentiate them from the experiments with light, called photo-Fenton. The fact that the term dark was not used for the dark processes, and only the name Fenton may have caused this confusion. Their results are shown in graphs 1 and 3 and the kinetics in Table 1, also discussed in the text.
- Why authors perform up to pH 5? Authors should include different pH condition including neutral pH.
pH 5 has been chosen as a pH far from the optimum conditions of pH 3, which is a pH where we know that the activity of humic-like substances is quite remarkable. The Interactions between humic-like complexing substances and complexation due to the presence of contaminants become less clear as the pH increases, and the formation of insoluble and inactive species becomes more important. On the other hand, at lower pH the precipitation of iron is lower and the effect of complexation of humic-like substances would not be evident either. It is of interest to study these effects at pH as close to neutral as possible once we have a better understanding of the system from these studies. A paragraph on the lines (79-82) has been added justifying the use of this pH and a citation (reference 21) has been included.
Reviewer 2 Report
The topic of the manuscript is interesting.I highly appreciate the description of the experiences. Unfortunately, the experiments should be repeated several times (2-3 times) before they are described in the form of a publication. Unfortunately, the researchers describe the experiments performed only once. There are no standard deviations for the individual measurement points. Therefore, describing and comparing the results that differ by only a few percent (e.g., line 236: 9 and 17%) is unreasonable and wrong. On this basis, it is inappropriate to make any conclusions.
Author Response
Reviewer #2:
The authors would like to thank the reviewers for their helpful and constructive comments and the editor for giving us the opportunity to improve the quality of the manuscript. Responses are indicated in blue in the following paragraphs and corresponding changes in the new version of the manuscript are highlighted in yellow. The whole manuscript has been reviewed in order to improve both the content and the quality of it. There are new paragraphs in every section of the manuscript.
The topic of the manuscript is interesting. I highly appreciate the description of the experiences. Unfortunately, the experiments should be repeated several times (2-3 times) before they are described in the form of a publication. Unfortunately, the researchers describe the experiments performed only once. There are no standard deviations for the individual measurement points. Therefore, describing and comparing the results that differ by only a few percent (e.g., line 236: 9 and 17%) is unreasonable and wrong. On this basis, it is inappropriate to make any conclusions.
Thank you for your comments. With the incorporation of the reviewers' suggestions we feel that the quality of the manuscript has been improved.
Regarding the comments about duplication of experiments, it should be said that these were performed at least twice in all cases. In the first version, although this fact was mentioned in the experimental part, we made the mistake of not including the error bars in the graphs. Following your recommendation, they have been included in almost all the graphs. Our errors are in the range of 4-10% depending on the experiment. Differences between conditions are always more significant than the experimental error determined and the reference values that have been cited in the revised manuscript show larger variations (see lines 257-267). Therefore, we consider that the discussions or conclusions we have made having the error calibrated, are adequate.
Author Response File: 
Author Response.pdf
Round 2
Reviewer 1 Report
Accept
Reviewer 2 Report
-
