Intensification of a Neutralization Process for Waste Generated from Ion Exchange Regeneration for Expansion of a Chemical Manufacturing Facility

Round 1

Reviewer 1 Report

I suggest to to review the introduction

Author Response

The authors would like to thank the reviewer for the comments that have helped in significantly improving the manuscript. Our response to each comment is provided below. Changes to the original submitted manuscript have been made using the “change tracking” function in Microsoft word.

Review Comment: I suggest to review the introduction.

Authors’ response: We thank the reviewer for positive assessment of our manuscript. As per the suggestion, the introduction has been revised considerably. Please refer to the revised manuscript attached.

Author Response File: Author Response.docx

Reviewer 2 Report

Dear authors,

Your work is interesting, however, some improvement  can be done

Introduction

 This part can be modified by:

a) adding more references. Some parts, i.e. line 80 or in the paragraph from line 80 to line  91.

b) reorganization information. It was difficult for me to understand the different ways that exist to treat the water.  Maybe you can reorganize this information 

In my opinion, the following section can be moved to result section or at least canceled from the introduction "The improved neutralization setup proposed in this work has achieved 63% reduction in volume of IX regeneration waste stream which would otherwise require treatment; a 62% reduction in the capital cost; and 55% reduction in operating cost"

Maybe a graph abstract can be done 

 

 

 

 

Author Response

The authors would like to thank the reviewer for the detailed comments that have helped in significantly improving the manuscript. Our response to each comment is provided below. Changes to the original submitted manuscript have been made using the “change tracking” function in Microsoft word.

Reviewer comment: Your work is interesting, however, some improvement can be done.

Authors’ response: We thank the reviewer for positive assessment of our manuscript.

Reviewer comment: Introduction

 This part can be modified by:

91. a) adding more references. Some parts, i.e. line 80 or in the paragraph from line 80 to line  91.

Authors’ response: We thank the reviewer for this comment. We have now added new references and have them listed as per the journal reference guidelines.

1. b) reorganization information. It was difficult for me to understand the different ways that exist to treat the water.  Maybe you can reorganize this information 

In my opinion, the following section can be moved to result section or at least canceled from the introduction "The improved neutralization setup proposed in this work has achieved 63% reduction in volume of IX regeneration waste stream which would otherwise require treatment; a 62% reduction in the capital cost; and 55% reduction in operating cost"

Authors’ response: We thank the reviewer for suggesting ways to improve the readability of the manuscript. We have now deleted the section mentioned from the introduction. We have restructured and reorganized the manuscript to make it more readable.

Reviewer comment: Maybe a graph abstract can be done 

Authors’ response: Figure 4 can be used in the abstract as the optimized neutralization setup

Author Response File: Author Response.docx

Reviewer 3 Report

The authors described an improvement of the neutralization setup for ion exchange regeneration wastewater. This topic seems to be actual and could be interesting for the reader. However, I have many concerns listed below:
1) First of all, the English style should be carefully checked. There are many complicated sentences blurry the sense.
2) Abstract is too long and contains some unimportant information.
3) Introduction part is very unclear, the aims of the study are presented in many places making them difficult to find. Also, many statements are not supported with proper references. From line 92 you put many paragraphs with a discussion about the result - this is not appropriate for the introduction part.
4) Equation 3 and 4 - What is happening with cations Ca (2+) and Na (+)? Moreover, Eq. 4 should be Cl (-) instead of Cl(+).
5) Methods and discussion part - there is almost no supporting reference.  In my opinion, all things you did are unclear. There is no precise explanation nor calculations as, why you are proposing some of the solutions. Were you based on your own experience? There are only calculations that consider costs, but again no reference to understand how the prices were estimated.
6) The whole idea was to design an improved neutralization setup. Without any experiment conducted or, at least, some process calculation/modeling, we don't even know how efficient it will be working. 
In my opinion, some extensive studies should be conducted to test and prove the proposed setup, this could be done even on a small, laboratory scale. Without it is more like speculation for me, instead of research.
Because of the abovementioned flaws, I suggest the manuscript be rejected in the current form.

Author Response

The authors would like to thank the reviewer for the detailed comments that have helped in significantly improving the manuscript. Our response to each comment is provided below. Changes to the original submitted manuscript have been made using the “change tracking” function in Microsoft word - see attached.

The authors described an improvement of the neutralization setup for ion exchange regeneration wastewater. This topic seems to be actual and could be interesting for the reader. However, I have many concerns listed below:
Reviewer comment: 1) First of all, the English style should be carefully checked. There are many complicated sentences blurry the sense.

Authors’ response: We thank the reviewer for this comment. We have restructured the revised manuscript to eliminate confusing sentences.  

Reviewer comment: 2) Abstract is too long and contains some unimportant information.

Authors’ response: The abstract has been revised considerably. We have eliminated unimportant information and the abstract is now limited to 200 words, as per the journal guidelines.

Reviewer comment: 3) Introduction part is very unclear, the aims of the study are presented in many places making them difficult to find. Also, many statements are not supported with proper references. From line 92 you put many paragraphs with a discussion about the result - this is not appropriate for the introduction part.

Authors’ response: We thank the reviewer for their valuable comment. We have revised the introduction considerably. Please see the revised manuscript.

Reviewer comment: 4) Equation 3 and 4 - What is happening with cations Ca (2+) and Na (+)? Moreover, Eq. 4 should be Cl (-) instead of Cl(+).

Authors’ response: We thank the reviewer for this question. During the regeneration step, Ca²⁺ or Na⁺ ions attached to the cation resin bed are replaced with H⁺ ions from H₂SO₄ resulting in formation of CaSO₄ or Na₂SO₄ in the waste stream. Similarly, Cl^- or NO₃^- ions attached to the anion bed are replaced by OH^- ions from NaOH to form NaCl or NaNO₃ in the waste stream. We have added this text in the manuscript for providing the explanation.

We thank the reviewer for the typographical error. We have corrected Cl(-) ion in the manuscript.

Reviewer comment: 5) Methods and discussion part - there is almost no supporting reference.  In my opinion, all things you did are unclear. There is no precise explanation nor calculations as, why you are proposing some of the solutions. Were you based on your own experience? There are only calculations that consider costs, but again no reference to understand how the prices were estimated.

Authors’ response: We thank the reviewer for these questions. We agree that we should have included specific details of the existing and the new neutralization processes to substantiate our conclusions. In the revised manuscript, Table 1 shows the various streams from the IX regeneration. In section 2.2 additional discussion is added to explain the operation of the neutralization process in terms of the dilute (cation backwash, cation fast rinse, anion warmup, anion backwash and anion fast rinse)  and concentrated (Cation 2% acid regen, cation 5% acid regen, cation slow rinse, anion 5% base rinse, anion slow rinse) streams, Analysis of dilute streams has shown that they do not need to be neutralized, and only concentrated streams are sent for neutralization to the neutralization setups designed in this work. For cost estimation and other calculations more details have been added to sections 2.4 – 2.7 of the manuscript to quantitatively justify the improvements in the new process. During design of the new facility, we were required to add additional IX capacity as a result of which the IX regeneration waste neutralization setup was required to be debottlenecked. During the design phase several neutralizations setup’s were conceptualized and are discussed in this manuscript. The various solutions show the evolution of the design and progressively show improvement in operating and capital cost. Several lab studies were also performed to select which streams can be discarded without treatment – details added to section 3.4 of the manuscript. Environmental approval was required to change the existing process of treating all effluent streams from IX regeneration. The revised manuscript shows that the pH of the dilute streams was measured and found to be in acceptable pH range suggesting those streams do not contain high concentration of acid or base. This exercise alone reduced the volume of waste treatment by 63%. The reduced volume also reduced the equipment sizes and the time required for the unit operation.

Reviewer comment: 6) The whole idea was to design an improved neutralization setup. Without any experiment conducted or, at least, some process calculation/modeling, we don't even know how efficient it will be working. 
In my opinion, some extensive studies should be conducted to test and prove the proposed setup, this could be done even on a small, laboratory scale. Without it is more like speculation for me, instead of research.

Authors’ response: This is a valid criticism of our manuscript. We have now added experimental data in section 3 of the manuscript. As per the experimental results the dilute streams (cation backwash, cation fast rinse, anion warmup, anion backwash and anion fast rinse) were analyzed and the environmental group of the site concluded that the streams did not contain any acid/ base and was within the acceptable pH rage to be disposed to the outfall without waste treatment. The dilute streams have been consistently monitored for some time now which supports our experimental finding. The neutralization volume has also been reduced, which decreases the time required for neutralization, equipment size, and capital and operating cost of the proposed neutralization setups. Another lab study is added to the manuscript that shows the need for improved mixing that is achieved in the above ground neutralization tanks through angled eductors. Other setup’s that were conceptualized during the evolution of the design are discussed to show how one can achieve effective neutralization with reduced capital cost. The shortcoming of the first and second neutralization setup have been highlighted in the results section and the reasons for selecting the improved neutralization setup is also reemphasized. 

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Thank you very much for providing an improved manuscript version. In the current form, the abstract and introduction parts are more clear. You added a lot of key explanations to methods and descriptions of three new neutralization setups. Now it makes more sense to me. 

Now I would like to show you only a few additional things:

1) lines 64-66 and 77-78 repetition of the same information

2) some editorial errors in lines 89, 102, 147

3) Table 1 - you should name the column with the m3 symbol

4) You write in many places optimal, most optimal, etc. for instance lines 73, 83. In my opinion, you should use improved or more efficient instead. There is no evidence this is an optimal (so maximized) solution, I can only agree this is improved, cause it requires for example less cost. 

5) The main weakness of this work is the lack of evidence of how this improved setup will work. In the current version, you added information, that you were using the ASPEN tool to verify it, so it is better than in the previous form.  However, still, some experiments should be done to verify it. Nevertheless, to design a new solution this could be enough, but you cannot forget to validate the computer solution. Therefore, I accept the current version of the manuscript after some small corrections.

Author Response

The authors would like to thank the reviewer for the detailed comments that have helped in significantly improving the manuscript. Our response to each comment is provided below. Changes to the original submitted manuscript have been made using the “change tracking” function in Microsoft word.

Reviewer comment: Thank you very much for providing an improved manuscript version. In the current form, the abstract and introduction parts are more clear. You added a lot of key explanations to methods and descriptions of three new neutralization setups. Now it makes more sense to me. 

Authors’ response: We thank the reviewer for positive assessment of our manuscript.

Reviewer comment: Now I would like to show you only a few additional things:

1) lines 64-66 and 77-78 repetition of the same information

Authors’ response: We thank the reviewer for pointing out the redundant statement. The statement in lines 77-78 is removed

Reviewer comment: 2) some editorial errors in lines 89, 102, 147

Authors’ response: We thank the reviewer for pointing out the editorial errors. The errors have been addressed in the revised manuscript.

Reviewer comment: 3) Table 1 - you should name the column with the m3 symbol

Authors’ response: We thank the reviewer for the comment. Description “Effluent volume” has been added before the m3 symbol.

Reviewer comment: 4) You write in many places optimal, most optimal, etc. for instance lines 73, 83. In my opinion, you should use improved or more efficient instead. There is no evidence this is an optimal (so maximized) solution, I can only agree this is improved, cause it requires for example less cost. 

Authors’ response: We thank the reviewer for the observation. We have changed the words in line 73, 83, 280 from “optimal” to “efficient”.

We have also replaced “optimized” in lines 12, 17, 76, 193 with “efficient” and removed the word optimized from Figure 7.

Reviewer comment: 5) The main weakness of this work is the lack of evidence of how this improved setup will work. In the current version, you added information, that you were using the ASPEN tool to verify it, so it is better than in the previous form.  However, still, some experiments should be done to verify it. Nevertheless, to design a new solution this could be enough, but you cannot forget to validate the computer solution. Therefore, I accept the current version of the manuscript after some small corrections.

Authors’ Response: We thank the reviewer for the feedback. We have included results of experiments that were performed to ensure that the engineered design will work. We have also included text in the manuscript “The dilute streams were then directed to the outfall 2 for several months and the measured pH of the outfall was found to stay within the desired range of 7-8 pH as shown by the plant data” lines 301-303, outlining that the dilute streams have been directed to an outfall without treatment at the site based on the experiments outlined in this study. We feel confident that the commercial scale of the design will work as anticipated. We are very thankful of the reviewer for providing us valuable comments that has enabled us to significantly improve the manuscript.

Author Response File: Author Response.docx