Recent Advances in Advanced Oxidation Processes for Degrading Pharmaceuticals in Wastewater—A Review
, Jun-Wei Lim 4,5 and Anwar Usman 1,*
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe review addresses the current forefront in wastewater treatment, presenting a well-structured and lucid framework that aligns with the journal's requirements and captivates readers' interest. However, focusing specifically on the field of TiO2-based photocatalysis, the content appears somewhat lacking. The review of existing research lacks depth, and the prospective outlook on future research directions lacks novelty and specificity, failing to adequately highlight the advanced nature of photocatalysis in pharmaceutical treatment in wastewater.
Here are specific recommendations for improvement:
1. The title of the manuscript suggests a broad overview of advanced oxidation technologies for pharmaceutical degradation in wastewater. However, the emphasis and detailed discussion focus primarily on TiO2-based photocatalytic degradation, creating a mismatch. Consider revising the title to accurately reflect the content.
2. Considering the highlighted emphasis on TiO2-based photocatalytic degradation in the abstract, you may consider reducing the detailed discussion on various advanced oxidation technologies. Emphasize the exploration of photocatalytic materials, the unique advantages and research value of TiO2 photocatalysis, extending the discussion to the combined use of TiO2 photocatalysis with other technologies.
3. In section 3.3 Ozone-based processes, the discussion regarding the ozone in pollutant degradation emphasizes both direct and indirect oxidation. In reality, within the realm of indirect oxidation, apart from the mentioned combined techniques, another more commonly employed method is catalytic ozonation. This approach significantly enhances the efficiency of pollutant degradation. It is essential to supplement this information in the manuscript.
4. Provide a more focused discussion on the application of TiO2 photocatalytic materials in the degradation of pharmaceuticals in wastewater. Clearly delineate the advantages, such as enhanced pollutant degradation, inhibition of toxic byproduct generation and so on.
5. Investigate whether TiO2 photocatalytic technology described in the manuscript has industrial applications. If applicable, provide examples and analysis; if not, analyze the reasons and propose future application directions.
6. Some related papers (e.g., Chinese Chemical Letters 34(4) (2023) 107541; Acta Physico-Chimica Sinica 38(7) (2022) 2201008; Journal of Hazardous Materials 384 (2020) 121494; Rare Metals 2023 https://doi.org/10.1007/s12598-023-02499-3) are suggested to cited and discussed.
7. On Page 15, Line 591, there is a missing period at the end of the sentence. Please carefully review the entire manuscript to avoid such errors.
Comments on the Quality of English LanguageNA
Author Response
Reviewer 1
The review addresses the current forefront in wastewater treatment, presenting a well-structured and lucid framework that aligns with the journal's requirements and captivates readers' interest. However, focusing specifically on the field of TiO2-based photocatalysis, the content appears somewhat lacking. The review of existing research lacks depth, and the prospective outlook on future research directions lacks novelty and specificity, failing to adequately highlight the advanced nature of photocatalysis in pharmaceutical treatment in wastewater. Here are specific recommendations for improvement:
Comment 1: The title of the manuscript suggests a broad overview of advanced oxidation technologies for pharmaceutical degradation in wastewater. However, the emphasis and detailed discussion focus primarily on TiO2-based photocatalytic degradation, creating a mismatch. Consider revising the title to accurately reflect the content.
Our response: Thank you for your suggestion. We think that it would have been interesting to explore the aspect of pharmaceutical degradation using different advanced oxidation technologies and not limited to photocatalysis. The emphasis and detailed discussion on TiO2-based photocatalysis is unavoidable as this topic is really well studied. Therefore, we would like to keep the current title.
Comment 2: Considering the highlighted emphasis on TiO2-based photocatalytic degradation in the abstract, you may consider reducing the detailed discussion on c Emphasize the exploration of photocatalytic materials, the unique advantages and research value of TiO2 photocatalysis, extending the discussion to the combined use of TiO2 photocatalysis with other technologies.
Our Response: Thank you for your comment. We did not reduce the detailed discussion on advanced oxidation technologies, instead we have added the exploration of other photocatalytic materials as outlined in section 3.5, page 12, line 388-398, line 402-408; section 5, page, 17, line 640-644.
Comment 3: In section 3.3 Ozone-based processes, the discussion regarding the ozone in pollutant degradation emphasizes both direct and indirect oxidation. In reality, within the realm of indirect oxidation, apart from the mentioned combined techniques, another more commonly employed method is catalytic ozonation. This approach significantly enhances the efficiency of pollutant degradation. It is essential to supplement this information in the manuscript.
Our Response: We agreed with the reviewer’s comment. Accordingly, we have included a discussion on catalytic ozonation approach in section 3.3, page 10, line 306-325.
Comment 4: Provide a more focused discussion on the application of TiO2 photocatalytic materials in the degradation of pharmaceuticals in wastewater. Clearly delineate the advantages, such as enhanced pollutant degradation, inhibition of toxic byproduct generation and so on.
Our Response: We thank the reviewer for her/his comment. We have outlined in detail the application of TiO2 photocatalytic materials and its advantages in Section 3.5, page 11, line 366-381, and in Section 4, line 489-496; and section 6 on the reported studies photodegradation using these materials.
Comment 5: Investigate whether TiO2 photocatalytic technology described in the manuscript has industrial applications. If applicable, provide examples and analysis; if not, analyze the reasons and propose future application directions.
Our Response: We have accordingly added a new section (Section 7) specific for future industrial application in page 17, line 655 – 695, and comparing results from pilot tests of the remediation of real wastewater using different AOPs techniques and addressing possible limitations for large-scale use.
Comment 6: Some related papers (e.g., Chinese Chemical Letters 34(4) (2023) 107541; Acta Physico-Chimica Sinica 38(7) (2022) 2201008; Journal of Hazardous Materials 384 (2020) 121494; Rare Metals 2023 https://doi.org/10.1007/s12598-023-02499-3) are suggested to cited and discussed.
Our Response: Thank you for this suggestion. We have cited these papers in section 3.5, page 12, line 393-398; and page 12, line 402-408.
Comment 7: On Page 15, Line 591, there is a missing period at the end of the sentence. Please carefully review the entire manuscript to avoid such errors.
Our Response: Thank you for pointing this out. We have reread this manuscript carefully and corrected all mistakes and grammatical errors. The entire manuscript has been checked and reviewed to avoid the errors, including the missing period at the end of the sentence.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript titled “Recent advances in advanced oxidation processes for degrading pharmaceuticals in wastewater – A review” reports on using AOP for remediation of pharmaceuticals in wastewater. The manuscript in its current state provides little novelty as there are already several publications on the same topic which is quite saturated. To improve the quality and novelty of the manuscript, the following comments should be considered.
· Table 1 includes various pharmaceuticals commonly found in wastewater. For general comparison, their relative concentration detected in wastewater in various surveys should be provided in the table as well.
· The introduction should provide tolerance limits of various drugs in order to judge the relative toxicity of these drugs as compared to other pollutants such as heavy metals and organic dyes. The role of pKa, pH, and other similar factors should be discussed.
·
· Besides pharmaceutical drugs, endocrine-disrupting drugs such as estrogenic hormones should be included, which are more potent and bioaccumulative.
· Bibliometric analysis of various AOP methods using Web of Sience database can be provided by using VOSviewer software.
· Reported literature studies for the ultrasonication and ozonation section should be provided to elaborate on their status in comparison to other techniques. Currently, the section is just a basic description of these processes without any results from the literature.
· A table should be provided illustrating the pros and cons of each AOP method for drugs removal. Electrical energy per Order (EEO) should be included as well for relative selection of methods.
· Full form of equations of each generative molecular species should be provided in equation form. Line numbers 210 to 213.
· A separate section on the influencing factors for different AOP processes should be discussed.
· The photocatalytic AOP process is limited in scope. Results on advanced photocatalytic studies should be included. For example: https://doi.org/10.1016/j.jphotochem.2023.114733, can be included as examples of recent studies.
· Since, photocatalysis is the most active field of AOP, detailed strategies which are currently being implemented to improve photocatalytic activity in visible light range should be provided. These strategies mostly involve engineering surface defects, plasmonic materials, doping, and the formation of heterojunction. For a detailed description, the following article can be taken as a reference guidance. Ref: https://doi.org/10.1016/j.jece.2023.111541
· Commonly used photocatalysts should be provided graphically along with their relative bandedge positions. For organic pollutants degradation, photocatalysts with a more positive valence band edge position are preferred. It is because degradation primarily proceeds via the oxidative pathway. Such discussion should be included. Ref above sample figure of most commonly used photocatalysts.
Multifunctional properties of photocatalytic materials should be included, as these materials are not only effective for pharmaceuticals but also for antibacterial activities and self cleaning properties.
· Comparison of AOP processes with other techniques for removal of contaminants should be discussed, such as membrane technology and adsorptive materials.
Author Response
Reviewer 2
The manuscript titled “Recent advances in advanced oxidation processes for degrading pharmaceuticals in wastewater – A review” reports on using AOP for remediation of pharmaceuticals in wastewater. The manuscript in its current state provides little novelty as there are already several publications on the same topic which is quite saturated. To improve the quality and novelty of the manuscript, the following comments should be considered.
Comment 1: Table 1 includes various pharmaceuticals commonly found in wastewater. For general comparison, their relative concentration detected in wastewater in various surveys should be provided in the table as well.
Our Response: Thank you for this suggestion. However, the relative concentration of pharmaceuticals is not critically high in most wastewater systems as mentioned in page 4, line 167-170.
Comment 2: The introduction should provide tolerance limits of various drugs in order to judge the relative toxicity of these drugs as compared to other pollutants such as heavy metals and organic dyes. The role of pKa, pH, and other similar factors should be discussed.
Our Response: Thank you for this comment. The concentration of various drugs is relatively low in comparison to other organic pollutants, such as synthetic dyes. We have added additional discussion on the role of pKa, pH, and other similar factors in section 4, page 14, line 497-522.
Comment 3: Besides pharmaceutical drugs, endocrine-disrupting drugs such as estrogenic hormones should be included, which are more potent and bioaccumulative.
Our Response: We thank the reviewer for her/his comment. We have included endocrine-disrupting drugs in section 6, page 17, line 640-644, and section 3.5, page 12, line 402-408.
Comment 4: Bibliometric analysis of various AOP methods using Web of Sience database can be provided by using VOSviewer software.
Our Response: Thank you for this suggestion, however, there are plenty of studies working on the analysis of various AOP methods as we mentioned in page 3, line 131-132.
Comment 5: Reported literature studies for the ultrasonication and ozonation section should be provided to elaborate on their status in comparison to other techniques. Currently, the section is just a basic description of these processes without any results from the literature.
Our Response: We agreed with the reviewer for her/his comment. Accordingly, we provide some results obtained from literature as discussed in page 10, line 319-324; and page 11, line 343-348.
Comment 6: A table should be provided illustrating the pros and cons of each AOP method for drugs removal. Electrical energy per Order (EEO) should be included as well for relative selection of methods.
Our Response: To date, there is still partial analysis on energy consumption with lack of comprehensive studies and reports in literature. It is also difficult to compare EEO values because the electrical prices vary from country to country.
Comment 7: Full form of equations of each generative molecular species should be provided in equation form. Line numbers 210 to 213.
Our Response: We have provided the equations of each molecular species in page 7, line 212-217.
Comment 8: A separate section on the influencing factors for different AOP processes should be discussed.
Our Response: We have added a separate section on the influencing factors (Section 4) for different AOP processes on page 13, line 449-522.
Comment 9: The photocatalytic AOP process is limited in scope. Results on advanced photocatalytic studies should be included. For example: https://doi.org/10.1016/j.jphotochem.2023.114733, can be included as examples of recent studies.
Our Response: We have discussed the photocatalytic AOP process in more detail and included this reference in page 17, line 640-644.
Comment 10: Since, photocatalysis is the most active field of AOP, detailed strategies which are currently being implemented to improve photocatalytic activity in visible light range should be provided. These strategies mostly involve engineering surface defects, plasmonic materials, doping, and the formation of heterojunction. For a detailed description, the following article can be taken as a reference guidance. Ref: https://doi.org/10.1016/j.jece.2023.111541
Our Response: A mention of using and fabricating visible-light-responsive catalyst, including the involvement of engineering surface defects, plasmonic materials, doping, and the formation of heterojunction is outlined in page 11, line 380-408. The following article recommendation has been added into the manuscript, line 388-393.
Comment 11: Commonly used photocatalysts should be provided graphically along with their relative bandedge positions. For organic pollutants degradation, photocatalysts with a more positive valence band edge position are preferred. It is because degradation primarily proceeds via the oxidative pathway. Such discussion should be included. Ref above sample figure of most commonly used photocatalysts.
Our Response: This discussion of the relative band edge has been summarized in page 12, line 410-423 with additional band edge diagram in Figure 2 in page 13.
Comment 12: Multifunctional properties of photocatalytic materials should be included, as these materials are not only effective for pharmaceuticals but also for antibacterial activities and self-cleaning properties.
Our Response: The multifunctional properties of photocatalytic materials have been included in line 369-375.
Comment 13: Comparison of AOP processes with other techniques for removal of contaminants should be discussed, such as membrane technology and adsorptive materials.
Response: The removal techniques, such as membrane technology and adsorptive materials was previously mentioned in line 78-95. When compared with AOP techniques, the membrane technology and adsorption are at some point impractical due to their post-treatment issues. Although, they are cheaper than AOPs, complete elimination of pollutants could not be achieved and do not occur instantaneously as AOP. We have outlined this point in more detail in Line 89-94: “It is worth noting that several key issues related to the post-adsorption steps to treat the pharmaceuticals remain crucial challenges [30]. Similar problems are also accounted for other techniques, such as flocculation, coagulation, and membrane filtration. From this point of view these techniques are less practical in comparison with AOPs, which could degrade the organic pollutants and pharmaceuticals instantaneously into smaller chemical compounds that could possibly be of less toxicities.”
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript is more or less improved after revision, and can be accepted.
Comments on the Quality of English LanguageModerate editing of English language required
Reviewer 2 Report
Comments and Suggestions for AuthorsRelevant suggestions have been considered. Therefore, manuscript can be accepted for potential publication.
