Kinetic Modeling of Brilliant Blue Discoloration by Ozonation

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript presents a study on the removal of Brilliant Blue dye from water using ozonation, exploring the effects of different ozone concentrations, pH conditions, and stirring on the reaction kinetics. The authors also propose a kinetic model for the process. While the topic is relevant and the authors have made significant efforts, there are several points that need further clarification and improvement:

1. The introduction should better emphasize the novelty of the kinetic model and how it advances current understanding compared to existing literature. Specifically, more focus should be placed on the limitations of classical kinetic models and why a chain-reaction approach is needed in this case.

2. The justification for using different pH levels (4, 7, and 10) should be expanded. Specifically, the impact of pH on the ozonation mechanism could be more deeply explored, especially regarding hydroxyl radical generation at high pH.

3. The integral method used for classical kinetic modeling is described, but the paper should discuss why it failed to provide interpretable results. This could be more detailed to help readers understand why a more complex model was required.

4. Ozone Supply Consistency: The manuscript mentions ozone supply but lacks details on the consistency and stability of ozone concentration during the experiments. More information on the precision and control of ozone concentration is necessary for reproducibility.

5. Improvement in Data Presentation: The figures showing kinetic curves (e.g., Figures 2, 3, 4) are difficult to interpret due to similar line styles and colors. Using more distinct colors and line types would enhance clarity. Additionally, some graphs lack proper axis labeling, especially units on time scales.

6. The section discussing the limitations of the classical kinetic models (Table 1) should be expanded. Negative rate constants and reaction order variations are reported, but the physical meaning of these results should be more clearly explained.

7. Toxicity of By-products: While the authors identify four degradation by-products using NMR, there is no discussion of their toxicity or environmental impact. The manuscript would benefit from a more thorough analysis of the potential risks posed by these by-products in real-world applications.

8. The model’s predictions should be discussed more in the context of its practical applications. For example, how does this kinetic model inform real-world wastewater treatment processes? Can the model be used to optimize ozonation conditions for industrial applications?

9. The conclusion should highlight the broader implications of the proposed kinetic model for future research and industrial applications. For instance, can this model be generalized for other triphenylmethane dyes or extended to more complex wastewater matrices?

Comments on the Quality of English Language

There are several grammatical errors and awkward phrasings throughout the manuscript. A thorough language revision is recommended to improve readability. Additionally, some technical terms are used without adequate explanation (e.g., "integral method" and "chained reaction system"), which could confuse readers unfamiliar with these concepts.

Author Response

Dear Reviewer 1

Thank you for objective observations. The authors express respectful thanks for careful and detailed analysis of our manuscript and for useful advice given for substantial improvement of the paper, in order to meet journal requirements for publication.

All the material completed is inserted in red in the original manuscript.

 

This manuscript presents a study on the removal of Brilliant Blue dye from water using ozonation, exploring the effects of different ozone concentrations, pH conditions, and stirring on the reaction kinetics. The authors also propose a kinetic model for the process. While the topic is relevant and the authors have made significant efforts, there are several points that need further clarification and improvement:

1. The introduction should better emphasize the novelty of the kinetic model and how it advances current understanding compared to existing literature. Specifically, more focus should be placed on the limitations of classical kinetic models and why a chain-reaction approach is needed in this case.

Classic kinetic models assume the chemical reaction to be rate-limiting and treat its mechanistic stages based on a Bodenstein-like approximation. The proposed model eliminates both simplifications, as it treats reaction chains explicitly and incorporates mass transfer kinetic. The introduction section was changed to incorporate your suggestion (Page 3, lines 115 - 124).

 

2. The justification for using different pH levels (4, 7, and 10) should be expanded. Specifically, the impact of pH on the ozonation mechanism could be more deeply explored, especially regarding hydroxyl radical generation at high pH.

The impact of pH on the ozonation mechanism was already discussed in the literature in a general manner. Relevant literature was cited where appropriate, including a self-citation [16] with the study of influencing factors from the authors' extensive research.

 

3. The integral method used for classical kinetic modelling is described, but the paper should discuss why it failed to provide interpretable results. This could be more detailed to help readers understand why a more complex model was required.
4. The section discussing the limitations of the classical kinetic models (Table 1) should be expanded. Negative rate constants and reaction order variations are reported, but the physical meaning of these results should be more clearly explained.

Observations 3 and 6: What fails in any attempt to use classic kinetic models is not the method by which it is applied (be it integral, differential or otherwise), but the model itself. Pseudo-order modelling is very simplistic and, at best, treats intermediate steps by steady-state-like approximations, while completely neglecting mass transfer. This can be valid only if the chemical step is rate-limiting and its intermediate stages satisfy the requirements of Bodenstein’s approximation, neither of which is true in our case. The introductory part of section 3.3 (dealing with kinetic analysis) was modified accordingly.

 

4. Ozone Supply Consistency: The manuscript mentions ozone supply but lacks details on the consistency and stability of ozone concentration during the experiments. More information on the precision and control of ozone concentration is necessary for reproducibility.

In Materials and Methods, the obtaining of ozone is specified and the measurement of its concentration continues with the UV photometer provided with the ozone generator. Ensuring a continuous flow of oxygen, ozone is generated in a constant, strictly controlled concentration. The flow rate is also constant, being measured by the flow meter of the device.

The reproducibility of BB FCF discoloration by ozonation was verified for each system studied. The authors did not think to include these calculations in order not to load the article with too much data. If you consider it appropriate to introduce them, we can do it as soon as possible.

 

5. Improvement in Data Presentation: The figures showing kinetic curves (e.g., Figures 2, 3, 4) are difficult to interpret due to similar line styles and colours. Using more distinct colours and line types would enhance clarity. Additionally, some graphs lack proper axis labelling, especially units on time scales.

Reviewer is right. We corrected accordingly.

Figures 2, 3 and 4 have been redone by changing the bullets and line thickness and color in each individual case to improve their visualization and interpretation. Because the curves obtained experimentally were too close and were difficult to analyze, enlarged details were made on the overlapping parts where they could not be visualized, leaving the upper right medapions (medallions), so that the reader can realize the allure of the curves. Also, in order to observe the overlap of the curves from the high ozone concentrations, the purple curve was made with a dotted line to see the green curve.

7. Toxicity of By-products: While the authors identify four degradation by-products using NMR, there is no discussion of their toxicity or environmental impact. The manuscript would benefit from a more thorough analysis of the potential risks posed by these by-products in real-world applications.

In the manuscript, the four secondary degradation products were specified, using NMR, to motivate the complexity of the dye structure and the possibility of the dye splitting depending on the attack conditions to motivate the need for a kinetic model. The toxicity of the dye and the secondary degradation compounds and/or their impact on the environment was discussed in a work dedicated to this subject self-cited in the bibliography at position [20].

 

8. The model’s predictions should be discussed more in the context of its practical applications. For example, how does this kinetic model inform real-world wastewater treatment processes? Can the model be used to optimize ozonation conditions for industrial applications?
9. The conclusion should highlight the broader implications of the proposed kinetic model for future research and industrial applications. For instance, can this model be generalized for other triphenylmethane dyes or extended to more complex wastewater matrices?

Observations 8 and 9: The authors, in this study, carried out in a first stage, a specific investigation for BB, following an extension to other triphenylmethane dyes, in this vast field, by proposing other research projects. Validation of the proposed model on real samples with such compositions will also be taken into account. After this stage, we will continue with process simulations to optimize the ozonation process.

 

Comments on the Quality of English Language

There are several grammatical errors and awkward phrasings throughout the manuscript. A thorough language revision is recommended to improve readability. Additionally, some technical terms are used without adequate explanation (e.g., "integral method" and "chained reaction system"), which could confuse readers unfamiliar with these concepts.

We apologize for these. We corrected and believe that there would be no more mistakes in English expression and/or spelling mistakes.

The authors considered that the technical terms like "integral method" and "chained reaction system", used in the work, are known by specialists in this field.

 

All these new contributions reflect the review requested by the Reviewer and we hope that this new form of work has answered your requests, for which we thank you.

 

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

1. Supplement the introduction part with an overview of studies that dealt with this issue.

2. Please chack typos through the manuscript.

3. Why did the authors not examine the influence of the concentration of the tested dye?

4. Are standard deviations available for the results?

5. Graphs must have x- and y-axis divisions.

6. Combine Figures 2-4, and add a figure with applied kinetic models (kinetic study). General comment, that all figures that can be combined.

7. It is necessary to compare the obtained data with similar studies and draw conclusions in accordance with the obtained results.

8. Do the authors have a suggestion for further development of this method?

9. Supplement the reference list with more recent papers.

Author Response

Reviewer 2

The authors express respectful thanks for careful and detailed analysis of our manuscript and for useful advice given for substantial improvement of the paper, in order to meet journal requirements for publication.

The entire text has been properly revised and adequate comments have been inserted in red in the original manuscript.

Brief answers to reviewer comments and suggestions are given below in order to indicate the revised parts into initial manuscript.

 

1. Supplement the introduction part with an overview of studies that dealt with this issue.

The authors introduce an overview of ozonation process in the Introduction of manuscript.

 

2. Please check typos through the manuscript.

We apologize for these. We believe that there would be no more mistakes in English expression and/or spelling mistakes.

 

3. Why did the authors not examine the influence of the concentration of the tested dye?

Dear reviewer, here in this work the concentration of the tested dye is the kinetic variable itself. As such, our study focused on the influence of the other parameters on its dynamics.

This article is only a part (the kinetics of the discoloration process by ozonation and the proposal of a kinetic model) of an extensive study of the Brilliant Blue FCF, the following were taken into account: the influence of the process factors (the concentration of both dye and the ozone, the pH of the solution, contact time, stirring, etc.). For this part of the study, the paper was published with the title “Discoloration of food from aqueous media by ozonation” in the U.P.B. Sci. Bull., Series B, Vol. 81, Iss. 3, 119 – 128, 2019, ISSN 1454-2331 by M. Marcvart, C. Constantin and L. Stoica (position 18 in Bibliography).

Then the toxicity of the dye was studied, published by M. Marcvart, I.E. Lucaciu, M. Nita Lazar, S. Gheorghe in the Rev. Chem, 71(4), 356 – 365, 2020, https://doi.org/10.37358/RC.20.4.8075 with the title „Considerations on the Toxicity of Brilliant Blue FCF Aqueous Solutions before and after Ozonation” (position 25 in Bibliography).

 

4. Are standard deviations available for the results?

Yes, we have the standard deviations calculated both for the samples analyzed and for the reproducibility of discoloration by ozonation, for each system studied. The authors did not think to include these calculations in order not to load the article with too much data. If you consider it appropriate to introduce them, we can do it as soon as possible.

 

5. Graphs must have x- and y-axis divisions.

Reviewer is right. We corrected accordingly.

Figures 2, 3 and 4 have been redone by changing the bullets and line thickness and color in each individual case to improve their visualization and interpretation. Because the curves obtained experimentally were too close and were difficult to analyze, enlarged details were made on the overlapping parts where they could not be visualized, leaving the upper right medapions (medallions), so that the reader can realize the allure of the curves. Also, in order to observe the overlap of the curves from the high ozone concentrations, the purple curve was made with a dotted line to see the green curve.

 

6. Combine Figures 2-4, and add a figure with applied kinetic models (kinetic study). General comment, that all figures that can be combined.

Excuse us, but we do not understand what exactly is wanted in this request.

 

7. It is necessary to compare the obtained data with similar studies and draw conclusions in accordance with the obtained results.

The classical models (pseudo-order 1 and 2) gave unphysical results (negative k), so the comparison with the experiment is irrelevant. The model proposed by us is original and for now we have no data from the literature for comparison.

 

8. Do the authors have a suggestion for further development of this method?

The authors, in this study, carried out in a first stage, a specific investigation for BB, following an extension to other triphenylmethane dyes, in this vast field, by proposing other research projects. Validation of the proposed model on real samples with such compositions will also be taken into account. After the validation of the proposed model, the process engineering will be another next stage incorporated in the process simulations to optimize the ozonation process.

 

9. Supplement the reference list with more recent papers.

The authors supplemented the reference list with five recent articles in this field.

 

All these new contributions reflect revision claimed by the Reviewer, and we hope that this new manuscript form is now satisfactory for publication.

 

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript describes a new approach to kinetic modeling of the discoloration reaction of Brilliant Blue color based on diffusion and a successive chained reaction system. The manuscript has great potential to be a very good paper but must be improved before publishing. There are unclear sentences, English should be improved, some mistakes need to be corrected, the results are not clearly visible in some figures, and some figures could be merged. All suggestions and comments are in the attached PDF file.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The authors should improve English in some parts of the manuscript. The parts are marked in the attached file.

Author Response

The authors express respectful thanks for careful and detailed analysis of our manuscript and for useful advice given for substantial improvement of the paper, in order to meet journal requirements for publication.

The entire text has been properly revised and adequate comments have been inserted in red in the original manuscript.

Brief answers to reviewer comments and suggestions are given below in order to indicate the revised parts into initial manuscript.

Thank you very much for the grammatical correction of the text. The authors replaced all the proposals and modified the phrases that were not understandable.

The Figure 5 is mention in the conclusion of section 3.2 were the authors speak for the first time about 1H-NMR mass spectrum of a sample of BB discoloration with ozone. If it is wrong, please tell us to change.

Preliminary - because these experimental data preceded the final action of building a kinetic model.

Figure 7 can't be together, in one graph, with Figure 6 because they are made in a special software that does not allow this.

Sincerely,
The authors

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors "3. Results and Discussions" Section should added some new  referenced, especially the content of discussion and analysis in the article .

 

Comments on the Quality of English Language

English language was fine

Author Response

Thank you very much for understanding!

The entire text has been properly revised and adequate comments have been inserted in green in the original manuscript.

All these new contributions reflect revision claimed by the Reviewer, and we hope that this new manuscript form is now satisfactory for publication.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors corrected manuscript so now it can be considered for publication.

Author Response

Thank you very much for the time allocated to the review and your patience!

Reviewer 3 Report

Comments and Suggestions for Authors

The authors improved the manuscript significantly. Suggestion to check the formatting of equations.

Author Response

Thank you very much for the time allocated to the review and your patience!

The authors change the formatting of equations.