Combining α-Al2O3 Packing Material and a ZnO Nanocatalyst in an Ozonized Bubble Column Reactor to Increase the Phenol Degradation from Wastewater
Round 1
Reviewer 1 Report
The article is devoted to the study of a new approaches to enhance the ozonation reaction to attain high phenol removal from wastewater. It was found, that the use of a ZnO nanocatalyst and α-Al2O3 combination allowed to achieved total phenol removal for a short period of time. The results presented in the article can be useful to a wide range of researchers. The article is written in clear language. To publish the article in the «Processes» journal, it is necessary to refine it in accordance with the comments presented below.
1. Has the type of dependency presented on the Fig. 4 changed if α-Al2O3 or a (ZnO + α-Al2O3 ) mixture was used?
2. What device was used to measure the bubble diameter? Can the values of bubble diameter with ozone gas alone and with ozone gas plus a ZnO nanocatalyst be within the measurement error?
3. What is the main conclusion was made from Fig. 7? Was pure ZnO phase in the catalyst?
4. It is necessary to show the SEM data of the samples after sonication. It will clearly demonstrate the enhance of the dispersion.
5. P. 9, line 287: according to the data at Fig. 11 must be another value for the phenol concentration of 25 ppm (not a 50.861).
6. P. 9, line 293: most likely, there is an error in the figure number.
7. Why only α-Al2O3 was more active compared to the ZnO nanocatalyst? Is the existence of a synergetic effect between α-Al2O3 and ZnO nanocatalyst in the experimental conditions possible?
Author Response
Response to the comments of Reviewer 1
Dear Reviewer,
Thank you very much for your effort in reviewing our manuscript. Fortunately, we have corrected the manuscript according to your useful comments. All the items that you mentioned are corrected and can be seen as blue text in the manuscript to facilitate the review process. Finally, we highly appreciate your notes as they allowed us to appropriately upgrade our manuscript.
Thank you with best regards
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The authors reported phenol mineralization with ozone in a bubble column reactor (BCR). The reaction was carried out in a fed-batch mode. The impact of superficial gas velocity on gas holdup and gas bubbles were characterized. The results were used to justify a flow of 2.5 m/s. In this set up, the benefits of using Al2O3 packing and ZnO nanoparticles in the reactor were evaluated. It was found adding Al2O3 and ZnO could increase the efficiency of phenol mineralization.
•Overall, this report is very preliminary. Much of the content was about literature summary and preparative work for conducting the research on the impact of Al2O3 and ZnO in the reactor. •There is not enough detail in the research conditions (Section 2.3) . The amount of packing and catalyst are missing. There is no description about KI test and how it was used to improve the understanding of the study. •The reaction design could have been better. Four conditions (Figure 3, line 153-154) were evaluated to compare the Al2O3 packing and ZnO nanoparticles. Then the evaluation should be side-by-side and the results should be presented together. For example, what are the conversions of 10 ppm phenol after 50 min ozonation with ozone, ozone + ZnO, ozone + Al2O3, ozone + ZnO + Al2O3? What are the required times to complete the mineralization under the four conditions? •The postulated mechanism is not supported by the experiment results. Kinetics (reaction rate) has not been systematically studied. Reaction intermediates were not characterized. There is no need to include Figure 15 (line 391-392) in the report.Line 34: "phenol is one of the dangerous materials" (chemicals)
Line 130: "perverted plate" (What is perverted, perforated?)
Line 119: "Semi-batch" (fed-batch)
Author Response
Response to the comments of Reviewer 2
Dear Reviewer,
Thank you very much for your effort in reviewing our manuscript. Fortunately, we have corrected the manuscript according to your useful comments. All the items that you mentioned are corrected and can be seen as red text in the manuscript to facilitate the review process. Finally, we highly appreciate your notes as they allowed us to appropriately upgrade our manuscript.
Thank you with best regards
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Please see comments and highlights in the document.
Specifically, second order kinetics does not make sense, because phenol degradation is not a reaction between two phenol molecules. It is a reaction of phenol with ozone (or reactive species from ozone). Therefore, removing the content of 2nd order reaction study is recommended.
Comments for author File: Comments.pdf
Careful editing is needed for publication.
Author Response
Response to the comments of Reviewer 2
Dear Reviewer,
Thank you very much for your effort in reviewing our manuscript. Fortunately, we have corrected the manuscript according to your useful comments. All the items that you mentioned are corrected and can be seen as red text in the manuscript to facilitate the review process. Finally, we highly appreciate your notes as they allowed us to appropriately upgrade our manuscript.
Thank you with best regards
Author Response File: Author Response.pdf
