Ozone for Industrial Wastewater Treatment: Recent Advances and Sector Applications

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Please find attached the file with the comments.

Comments for author File: Comments.pdf

Author Response

General Comment

This manuscript presents a comprehensive review of ozonation and its integration with advanced oxidation processes for industrial wastewater treatment. The authors have included a substantial body of literature covering various industrial sectors and wastewater types, demonstrating a thorough understanding of the current state of research in this field. I recommend accepting this manuscript following minor revisions.

Response: We sincerely thank the reviewer for their thoughtful and encouraging comments. We appreciate your recognition of the manuscript's comprehensiveness and relevance and are grateful for your recommendation to accept the manuscript with minor revisions. We have carefully considered your specific suggestions and revised the manuscript accordingly, as outlined below.

 

Specific Comments

1. Even though ozone is beneficial in disinfection and oxidation of organic compounds, it is very harmful to the human body and extremely corrosive to implement. Hence, the authors should incorporate a balanced discussion of ozone's highly toxic nature to human health, its extremely corrosive properties that necessitate specialized equipment and materials, and the associated safety protocols, and monitoring systems for safe industrial implementation.

Response: We agree with the reviewer that the toxic and corrosive nature of ozone gas is a critical consideration in industrial implementation. In response, we have added this point to Section 2.3 (now titled Challenges and Trade-Offs in Ozone Treatment), which discusses the practical limitations of ozonation. This revised section now includes mention of ozone’s health hazards, the need for ozone-compatible materials and corrosion-resistant components, and the importance of appropriate safety measures such as gas leak detection and ventilation systems. We believe this addition helps provide a more balanced and complete perspective.

2. The authors should consider addressing how ozonation can create intermediate by-products that may be more toxic than the parent compounds. Moreover, the complete mineralization of these newly formed byproducts often requires much higher ozone doses, leading to increased energy use and operational costs. This discussion would offer readers the ozonation's limitations and the potential need for additional treatment steps or enhanced monitoring to ensure the safety and effectiveness of the overall treatment process.

Response: Thank you for this important suggestion. We have expanded Section 2.3 to discuss the formation of potentially toxic oxidation byproducts (e.g., aldehydes, ketones, carboxylic acids, bromate) and the challenges associated with their removal. We have also noted that complete mineralization of organic compounds typically requires impractically high ozone doses, leading to greater energy consumption. The section now emphasizes the role of subsequent biological treatment steps (e.g., biofiltration, MBRs) in removing biodegradable intermediates and reducing residual toxicity. These additions help clarify the limitations of ozonation and the importance of integrated treatment approaches.

3. I recommend that the authors add a comprehensive summary table that brings together all the key findings from studies they reviewed. This table should clearly show what type of industrial wastewater was treated, how much ozone was used, which contaminants were targeted, and how well they were removed. Having everything laid out in a table like this would make the paper much more useful in practice. Readers could quickly scan through to find studies relevant to their specific situation and easily compare how well ozonation worked across different industries and applications.

Response: We appreciate this helpful recommendation. In response, we have created a new Table 1, which summarizes selected studies on ozone-based industrial wastewater treatment. The table includes industry sector, wastewater characteristics, treatment process configuration, ozone dose/contact time, targeted pollutants, and references. While not exhaustive, the table is designed to highlight representative studies across major industrial sectors and to facilitate practical comparison of treatment performance and operational conditions.

4. Minor mistakes

Response: We thank the reviewer for identifying these issues, and we have made the following corrections in the revised manuscript.

• Line 376, 379 better use doses instead of concentrations

Response: The term concentrations has been replaced with doses for clarity and accuracy in the context of ozone application.

• Line 436. The number 3 in ozone should be subscript.

Response: The formatting of ozone (O₃) has been corrected to include the proper subscript.

• Reference 4 contains errors (wasterwater ,advances )

Response: Typographical errors in the title have been corrected (“wasterwater” → “wastewater” and “advances” capitalization adjusted).

Reviewer 2 Report

Comments and Suggestions for Authors

Although this manuscript focuses on the application of ozone oxidation technology in the field of industrial wastewater treatment, its academic value fails to meet the publication requirements of this journal. Specific comments are as follows:

1. It only stays at the level of statement of the literature content, and lacks the systematic summary and theoretical refinement of the research results.
2. Although the application cases in food and beverage, textile, oil and gas industries are listed, the characteristics of wastewater in different industries and the suitability of ozone technology have not been cross-analyzed, and the general summary of “pollutant nature - process parameters - treatment efficiency” has not been constructed.
3. The discussion part is not deep enough and fails to show critical academic thinking.
4. Only describe the effect of ozone technology, but not analyze the controversial points of the existing research on the kinetic mechanism, secondary pollution and so on.
5. Failure to explore the attenuation of ozone's effectiveness in high salt systems, which cannot provide decision-making reference for industrial practice.
6. There is an obvious lack of technology comparison dimension, and no horizontal research scale has been established. When listing the application cases in various industries, ozone technology is not compared with other treatment technologies (e.g., Fenton oxidation, activated carbon adsorption) in terms of performance, environmental friendliness and other quantitative dimensions.

Author Response

General Comment

Although this manuscript focuses on the application of ozone oxidation technology in the field of industrial wastewater treatment, its academic value fails to meet the publication requirements of this journal.

Response: We appreciate the reviewer’s detailed critique and understand their perspective. However, we respectfully note that the intent of this manuscript is to provide a focused narrative review of recent research on ozone-based treatment technologies for industrial wastewater, rather than a systematic or meta-analytic study. Our goal was to synthesize recent findings, highlight practical applications and performance trends across industrial sectors, and identify key research gaps and considerations for implementation. In response to the reviewer’s concerns, we have revised the manuscript in several ways to improve clarity, depth, and balance. We hope that these revisions clarify the article’s purpose and strengthen its contribution to the field by offering a timely synthesis of ozone applications in industrial wastewater treatment.

 

Specific Comments

• It only stays at the level of statement of the literature content, and lacks the systematic summary and theoretical refinement of the research results.

Response: A concise summary of the literature search strategy and rationale for selecting industrial sectors has been added to the Introduction to clarify the scope and methodology of this narrative review.

• Although the application cases in food and beverage, textile, oil and gas industries are listed, the characteristics of wastewater in different industries and the suitability of ozone technology have not been cross-analyzed, and the general summary of “pollutant nature - process parameters - treatment efficiency” has not been constructed.

Response: While we acknowledge that constructing a generalized framework (e.g., pollutant–process–efficiency) across diverse industrial scenarios is valuable, the variability in wastewater matrices and treatment configurations limits the feasibility of such comparative analysis within the scope of this article. However, a summary table of representative studies is now included to help readers compare sector-specific findings.

• The discussion part is not deep enough and fails to show critical academic thinking.

Response: The Discussion section (Section 4) has been expanded to address challenges in real-world implementation, economic trade-offs, and future research needs.

• Only describe the effect of ozone technology, but not analyze the controversial points of the existing research on the kinetic mechanism, secondary pollution and so on.

Response: A new subsection (Section 2.3) has been added to discuss limitations of ozone treatment, including byproduct formation, energy demand, safety concerns, and material compatibility, as well as alternatives such as Fenton, membrane, and adsorption processes.

• Failure to explore the attenuation of ozone's effectiveness in high salt systems, which cannot provide decision-making reference for industrial practice.

Response: We thank the reviewer for this observation. While a detailed analysis of high-salinity systems is beyond the scope of this review, we have added a brief note in the relevant section (oil and gas) to acknowledge that salinity may attenuate ozone effectiveness through reduced solubility and radical scavenging, and that further research is needed to better understand ozone performance under these conditions.

• There is an obvious lack of technology comparison dimension, and no horizontal research scale has been established. When listing the application cases in various industries, ozone technology is not compared with other treatment technologies (e.g., Fenton oxidation, activated carbon adsorption) in terms of performance, environmental friendliness and other quantitative dimensions.”

Response: We acknowledge the reviewer’s suggestion to include a broader technology comparison. However, this review was intentionally focused on ozone-based processes and was not intended to serve as a horizontal comparison across treatment technologies. That said, we have expanded the discussion (Sections 2.3 and 4.2) to explicitly mention alternative approaches such as Fenton oxidation, UV-based AOPs, and adsorption, and to highlight the importance of site-specific evaluation when selecting appropriate treatment options.

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript is an extensive review on ozone and advanced ozone applications for industrial wastewater treatment. Here are some comments for its improvement:

1. The introduction section is way too short. Kindly extend it. also include the scope of the work and its broader implications.
2. Section 2.1: organic synthesis does not seem a fit for this paper, esp when the work is about wastewater treatment. it may be removed.
3. kindly discuss the mechanisms of action of ozone and adv ozone for contaminant oxidation.
4. For section 3, an extensive amount of data is presented. In some cases, the data can be better presented in the form of a table. also, the treatment efficiencies need to be reported as % removal for better comprehension.
5. The data for treatment is mostly presented for lab experiments. If possible, kindly present the efficiency data for actual industrial applications.

Author Response

General Comment

The manuscript is an extensive review on ozone and advanced ozone applications for industrial wastewater treatment.

Response: We thank the reviewer for their thoughtful comments and valuable suggestions, which have helped improve the clarity and impact of our manuscript. We have carefully considered each point and made revisions accordingly, as detailed below.

 

Specific Comments

• The introduction section is way too short. Kindly extend it. also include the scope of the work and its broader implications.

Response: We appreciate this suggestion. The introduction has been significantly expanded to better contextualize ozone-based technologies in industrial wastewater treatment. We now include a broader overview of industrial wastewater challenges, ozone’s unique role among treatment technologies, and the rationale for focusing on specific industry sectors. We also clarified the scope of the review and its implications for both researchers and practitioners.

• Section 2.1: organic synthesis does not seem a fit for this paper, esp when the work is about wastewater treatment. it may be removed.

Response: We agree with the reviewer’s observation. The former Section 2.1, which discussed organic synthesis-related applications of ozone, has been removed to maintain a focused and relevant narrative on wastewater treatment.

• Kindly discuss the mechanisms of action of ozone and adv ozone for contaminant oxidation.

Response: Thank you for pointing this out. While the manuscript does not include an in-depth description of ozone chemistry and mechanisms, we have added clarifying text in Section 2 directing readers, particularly those less familiar with ozone science, to foundational references and reviews. These resources provide detailed information on ozone decomposition, hydroxyl radical generation, and reaction pathways relevant to aqueous systems.

• For section 3, an extensive amount of data is presented. In some cases, the data can be better presented in the form of a table. also, the treatment efficiencies need to be reported as % removal for better comprehension.

Response: We appreciate this suggestion. In response, we created a new Table 1, which summarizes representative studies across industrial sectors, including wastewater characteristics, treatment processes, ozone doses, target pollutants, and references. While the reporting of treatment efficiency varies widely across the literature, we have used percentage removals where available and clarified this format wherever appropriate in the text. The table is intended to improve readability and allow for easier cross-sector comparison.

• The data for treatment is mostly presented for lab experiments. If possible, kindly present the efficiency data for actual industrial applications.

Response: We thank the reviewer for this comment. While our review focuses on peer-reviewed academic research rather than full-scale commercial deployments, we made a deliberate effort to include studies that used real industrial effluents collected from operational facilities. This is clarified in our Introduction (Methodology paragraph), where we note that studies using synthetic wastewater were excluded (with rare exceptions). However, we acknowledge that most of these studies were conducted at bench or pilot scale, which is a common limitation in academic research on industrial wastewater treatment technologies.

Reviewer 4 Report

Comments and Suggestions for Authors

Article entitled Ozone for Industrial Wastewater Treatment: Recent Advances and Sector Applications written by Daniel A. Leontieff, Keisuke Ikehata, Yasutaka Inanaga and Seiji Furukawa and submitted to Processes journal as a draft no 3679202 is a review article, dealing with an important issue of effective industrial wastewater treatment.

The article is in journal’s scope. Therefore, it could be considered for publication in processes journal. As English is not my native language, I am not able to assess language correctness. However, while reading, I found some statements missing, confusing or unclear. Below, I enclose the list of my comments.

Line 41: It is not true. Many review articles were published in field of ozone application for wastewater treatment, eg. : https://doi.org/10.1016/j.cep.2024.109852.

It would be valuable to include a methodology section at the beginning of the article. This section should explain how the authors searched for data to support the article: what the scope of the search was, which databases were reviewed, how many articles were initially identified, and what inclusion and exclusion criteria were applied. It should also state the time period considered in the review, and any other relevant details that define the approach used to gather and analyze the sources.

Section 2.1 is a bit out of topic.

Before discussing the applications of ozone, it is important to first provide a detailed description of its physical and chemical properties. These properties determine the possibilities and limitations of using ozone in wastewater treatment.

Since the paper suggests industrial applications, the review should be clearly divided into two distinct sections: one focusing on laboratory studies related to industrial wastewater treatment, and the other on actual full-scale industrial applications.

It would be helpful to add a summary table to each subsection in Chapter 3. The table should include information such as: what was done, how it was done, the effectiveness of the treatment, and a reference to the source.

Chapter 4 should be significantly expanded. It should include technological considerations related to the properties of ozone – for example, how to handle residual ozone and how it should be safely neutralized or disposed of.

Additionally, the chapter should present an economic analysis, including both capital (investment) and operational costs. It is also important to discuss the potential risks associated with the use of ozone in wastewater treatment.

What was the criterion for selecting the specific industries discussed in Chapter 3? Are there any contraindications for the use of ozone in other industries, or is it also being applied elsewhere?

The article contains numerous logical, substantive, and editorial shortcomings. In its current form, it is not suitable for publication. However, since this is a review paper, not an original research article, it can be revised and improved. The topic of using ozone for wastewater treatment is both important and interesting.

Therefore, based on my comments and overall impression, I recommend a major revision.

Author Response

General Comment

Article entitled Ozone for Industrial Wastewater Treatment: Recent Advances and Sector Applications written by Daniel A. Leontieff, Keisuke Ikehata, Yasutaka Inanaga and Seiji Furukawa and submitted to Processes journal as a draft no 3679202 is a review article, dealing with an important issue of effective industrial wastewater treatment.

The article is in journal’s scope. Therefore, it could be considered for publication in processes journal. As English is not my native language, I am not able to assess language correctness. However, while reading, I found some statements missing, confusing or unclear. Below, I enclose the list of my comments.

Response: We sincerely thank the reviewer for their careful evaluation and constructive feedback. We appreciate your recognition of the relevance and importance of ozone-based technologies for industrial wastewater treatment. In response to your suggestions, we have revised the manuscript substantially to improve its structure, clarity, and technical rigor. Below, we provide detailed responses to each of your comments.

 

Specific Comments

• Line 41: It is not true. Many review articles were published in field of ozone application for wastewater treatment, eg. : https://doi.org/10.1016/j.cep.2024.109852.

Response: We agree with the reviewer that there are many excellent review articles on ozonation for wastewater treatment in general, including the one suggested (which we have now cited in the revised manuscript). However, comprehensive reviews that focus specifically and exclusively on industrial wastewater applications, rather than municipal or general wastewater treatment, remain limited. We have clarified this distinction in the introduction to avoid any confusion.

• It would be valuable to include a methodology section at the beginning of the article. This section should explain how the authors searched for data to support the article: what the scope of the search was, which databases were reviewed, how many articles were initially identified, and what inclusion and exclusion criteria were applied. It should also state the time period considered in the review, and any other relevant details that define the approach used to gather and analyze the sources.

Response: Thank you for this suggestion. While we did not include a formal “Methodology” section, we have added a detailed paragraph at the end of the Introduction describing our review approach. This includes the use of the Web of Science database, key search terms, industry-specific filters, and the inclusion criteria (e.g., peer-reviewed studies using real industrial effluents). We also clarified the approximate time frame considered (past 20 years) and the rationale for selecting particular industry sectors.

• Section 2.1 is a bit out of topic.

Response: We agree, and we have removed Section 2.1 in the revised version to maintain the manuscript's focus on industrial wastewater treatment applications.

• Before discussing the applications of ozone, it is important to first provide a detailed description of its physical and chemical properties. These properties determine the possibilities and limitations of using ozone in wastewater treatment.

Response: We appreciate this comment. Rather than repeating well-established fundamentals, we now direct readers to authoritative resources in Section 2, which briefly introduces ozone's roles in wastewater treatment. This keeps the manuscript concise while still guiding novice readers to relevant foundational material.

• Since the paper suggests industrial applications, the review should be clearly divided into two distinct sections: one focusing on laboratory studies related to industrial wastewater treatment, and the other on actual full-scale industrial applications.

Response: We acknowledge the importance of distinguishing between scales of study. However, as stated in the methodology paragraph, this review focuses on peer-reviewed academic studies, most of which are bench- or pilot-scale investigations using real industrial wastewater. Full-scale industrial applications remain limited in academic literature. We have clarified this scope in the Introduction and throughout the manuscript to set appropriate expectations.

• It would be helpful to add a summary table to each subsection in Chapter 3. The table should include information such as: what was done, how it was done, the effectiveness of the treatment, and a reference to the source.

Response: Thank you for this valuable suggestion. While adding a separate table for each industrial sector was impractical, we have created a comprehensive summary table (Table 1) that captures key aspects of representative studies, including wastewater type, treatment configuration, ozone dose, targeted contaminants, and references. We believe this meets the reviewer’s intent and greatly improves usability.

• Chapter 4 should be significantly expanded. It should include technological considerations related to the properties of ozone – for example, how to handle residual ozone and how it should be safely neutralized or disposed of.

Response: We appreciate this comment. In the revised manuscript, Chapter 4 (Discussion) has been restructured and expanded into several subsections to improve clarity and depth, including a sector-based research summary with a comprehensive table (Table 1) and a focused subsection on economic considerations and future research needs.

To address the reviewer’s concern about engineering and safety considerations (e.g., ozone’s corrosive nature, gas handling, and safety protocols), we have added detailed content to Section 2.3: Limitations and Challenges of Ozonation. This section now discusses ozone’s toxicity to human health, the need for specialized materials and containment, monitoring systems, and safety measures required for safe industrial implementation.

• Additionally, the chapter should present an economic analysis, including both capital (investment) and operational costs. It is also important to discuss the potential risks associated with the use of ozone in wastewater treatment.

Response: Thank you for highlighting this. While detailed economic analysis was not feasible due to data limitations, we have added a dedicated subsection titled "Economic Considerations and Future Research Needs" (Section 4.2). This section discusses capital and operating cost factors, lack of cost standardization in the literature, and future research needs related to life-cycle assessments. We also discuss the potential risks of ozonation, including byproduct formation, toxicity of ozone gas, and energy demands, in Section 2.3.

• What was the criterion for selecting the specific industries discussed in Chapter 3? Are there any contraindications for the use of ozone in other industries, or is it also being applied elsewhere?

Response: We have clarified our selection criteria in the revised methodology paragraph in the Introduction. Industries were chosen based on both prior knowledge of ozone's practical relevance and the availability of recent peer-reviewed studies using real industrial wastewater. While ozone may be applicable in other sectors, the review focused on those with sufficient literature. We also acknowledge that in some settings (e.g., high-salinity systems), ozone’s performance can be limited — this is now addressed in the Oil & Gas subsection.

• The article contains numerous logical, substantive, and editorial shortcomings. In its current form, it is not suitable for publication. However, since this is a review paper, not an original research article, it can be revised and improved. The topic of using ozone for wastewater treatment is both important and interesting.

Response: We appreciate the reviewer’s candid assessment. In response to all reviewer comments, including yours, we have significantly revised the manuscript, including:

• Major restructuring of the Discussion section.
• Addition of a comprehensive summary table.
• Clarification of scope and methodology.
• Better articulation of ozone limitations and trade-offs.
• Expanded content on cost, safety, and practical challenges.

We believe the revised manuscript better reflects the current state of research and offers improved value for both academics and practitioners.

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

all the comments have been successfully incorporated and the manuscript may be accepted now.

Reviewer 4 Report

Comments and Suggestions for Authors

This is my second review of this manuscript. Authors answered all of my questions and comments. I find the authors' responses to be thorough, convincing, and appropriate. Suggested corrections have been applied. I suggest to accept this manuscript in its present form.