Oxidation of Florfenicol and Oxolinic Acid in Seawater by Ozonation
, Joon-Wun Kang 1 and Tae-Mun Hwang 2,*Round 1
Reviewer 1 Report
The authors investigated the removal of aquaculture antibiotics, namely florfenicol (FF) and oxolinic acid (OA), by seawater aquaculture. Overall, the paper was easy to understand, the approach adopted was systematic and scientifically sound, and the conclusion was adequately supported by the findings. Below are my specific comments/suggestions:
1) The authors used synthetic seawater that only contains bromide ions in a phosphate buffer. What differences in results are we expecting to see if real seawater is being used? In fact, can we really consider it as 'synthetic seawater' when all other ions were absent? e.g. a high bromide solution buffered at pH 8 is representative of seawater. The authors may also want to highlight the limitations in application of the findings.
2) The formation of bromate and chlorate ions were not mentioned. By ozonation of seawater, bromate is a dominant product. How does the presence of bromate affect the findings?
3) What are the expected products following the oxidative degradation of FF and OA?
4) The findings showed FF removal by ozone or bromine is very low compared to that of OA. The authors mentioned 'low reactivity' - can the authors explain why there is low reactivity?
5) OA removal was comparably effective by ozone alone or ozone + bromide. The authors emphasized that bromine is the main oxidant several times. Do the two sentences contradict each other? So what role does ozone play here? A catalyst / initiator? If there is no ozone, there is no bromine to start with.
6) Detailed derivations (eqn 9 and 22) should be provided in supplementary information.
7) Figure 4 was repeated twice.
8) Since all statistical calculations were performed in SPSS, mentioning one time in materials and methods is sufficient.
Author Response
COMMENTS FROM EDITORS AND REVIEWERS
- Review 1
The authors investigated the removal of aquaculture antibiotics, namely florfenicol (FF) and oxolinic acid (OA), by seawater aquaculture. Overall, the paper was easy to understand, the approach adopted was systematic and scientifically sound, and the conclusion was adequately supported by the findings. Below are my specific comments/suggestions:
Response: Thank you for your insightful comments and suggestions. In the following lines, we detail the changes and point-by-point response to your comments.
1) The authors used synthetic seawater that only contains bromide ions in a phosphate buffer. What differences in results are we expecting to see if real seawater is being used? In fact, can we really consider it as 'synthetic seawater' when all other ions were absent? e.g. a high bromide solution buffered at pH 8 is representative of seawater. The authors may also want to highlight the limitations in application of the findings.
Response: In our previous paper, reported in Chemical Engineering Journal 312 (2017) 30–38, we studied a kinetic study of ozone decay and bromine formation in saltwater (using sea salt from Sigma Aldrich) ozonation. In this study, we focused on the contribution of ozone and bromine, main oxidants in seawater ozonation. So, we determined the rate constants of target antibiotics, FF and OA, with ozone and bromine in synthetic seawater. All other ions were absent for simple kinetic modeling. Bromine solution buffered at pH 8 is fixed. Because the bromine is fractionated between HOBr and OBr- according average pH of seawater (pH = 8), HOBr is the predominant form to the pKa (HOBr ↔ OBr- + H+, pKa,bromine = 8.8).
2) The formation of bromate and chlorate ions were not mentioned. By ozonation of seawater, bromate is a dominant product. How does the presence of bromate affect the findings?
Response: Thank you for your critical comments for this manuscript. In saltwater ozonation, chloride and bromide react with ozone to produce chlorine and bromine with reaction rate constants of 0.003 M-1s-1 and 160 M-1s-1, respectively. Although saltwater contains approximately 280 times more chloride than bromide, the rate constant for the reaction of ozone with bromide is 50,000 times faster than that of the reaction with chloride. In fact, bromine is the main residual oxidant among the oxidants despite the much higher concentration of chloride compared with bromide. In our previous study, reported in Ozone Sci. Eng. 36 (2014) 515–525, the bromate formation was evaluated in seawater ozonation. Despite the high concentration of Br- (65 mg/L) in seawater, unexpectedly, BrO3- was not detected until an ozone dose of 5 mg/L.
3) What are the expected products following the oxidative degradation of FF and OA?
Response: The expected products by oxidation of FF are that the electrophilic attack on aromatic ring and the amino group of FF leading to the formation of mono-, di-, tri-, and tetra-FF. The expected products by oxidation of OA are the formation of -ethyl, -hydroxyl, and -dioxolo compound.
4) The findings showed FF removal by ozone or bromine is very low compared to that of OA. The authors mentioned 'low reactivity' - can the authors explain why there is low reactivity?
Response: The reactivity used in this manuscript means a reaction rate between target antibiotics and oxidants. Since the degradation rate of FA was less than that of OA, ‘low reactivity’ was used. However, it was corrected to ‘lower reactivity’ a relative expression to avoid confusion.
5) OA removal was comparably effective by ozone alone or ozone + bromide. The authors emphasized that bromine is the main oxidant several times. Do the two sentences contradict each other? So what role does ozone play here? A catalyst / initiator? If there is no ozone, there is no bromine to start with.
Response: In the case of ozone alone, it means that the experiment was performed in bromide free water. So, the ozone was a main oxidant in this case. When ozone was added to the synthetic seawater containing bromide ion, bromine was rapidly produced and acted as a main oxidant. The role of ozone in this case was an initiator.
6) Detailed derivations (eqn 9 and 22) should be provided in supplementary information.
Response: In order to understand the presented equation, the functions of eqn 9 and 22 are additionally presented in the manuscript. See the attached file.
Author Response File: 
Author Response.docx
Reviewer 2 Report
- Authors need to doublecheck all measuring units and chemical formulas, correct subscript and superscript where needed.
- English language and style need to be thoroughly checked - some sentences are difficult to understand
- Tables need to be arranged better
- Authors repeat the same informations one to many times
- Cited literature should be more up-to-date, authors could add newer references
- Figures are in wrong order and should be moved around in text to give better understanding of written text. It is tiresome to read something and then to look for figure which is much lower in text or even in another chapter
- Overall, my opinion is that the paper shows original data and is within the journal topic, however, the work should be presented in more comprehensive and clear way. Also article lacks fluidity and is it is difficult to follow the text because of numerous mistakes in writing, all the abreviations and mixing parts from methods chapter in results chapter.
Author Response
COMMENTS FROM EDITORS AND REVIEWERS
-Reviewer 2
Authors need to doublecheck all measuring units and chemical formulas, correct subscript and superscript where needed.
1) English language and style need to be thoroughly checked - some sentences are difficult to understand
Response: Thank you for your insightful comments and suggestions. The manuscript was revised again by native speaker.
2) Tables need to be arranged better
Response: Tables were rearranged.
3) Authors repeat the same information one to many times
Response: The duplicated information was corrected.
4) Cited literature should be more up-to-date, authors could add newer references
Response: References were rechecked.
5) Figures are in wrong order and should be moved around in text to give better understanding of written text. It is tiresome to read something and then to look for figure which is much lower in text or even in another chapter
Response: The order and position of the pictures were corrected.
6) Overall, my opinion is that the paper shows original data and is within the journal topic, however, the work should be presented in more comprehensive and clear way. Also article lacks fluidity and is it is difficult to follow the text because of numerous mistakes in writing, all the abreviations and mixing parts from methods chapter in results chapter.
Response: The manuscript was revised again for more clarification.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The authors have revised the manuscript as per reviewer comments. I am satisfied with the review response. The revised manuscript can be accepted and published in this journal.
