Levofloxacin Degradation, Antimicrobial Activity Decrease, and Potential for Water Disinfection Using Peroxydisulfate Activation by Ag/TiO₂ under Sunlight

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript reported the fabrication of Ag/TiO2 photocatalysts for degradation of levofloxacin and inactivation of E. coli. The corresponding mechanisms were also studied. These results are valuable to advance this area, and therefore the manuscript could be accepted after revision. The following issues should be addressed for revising this manuscript:

1.       Line 80-81, it is mentioned sulfate radical-based advanced oxidation technologies (PDS activation) have been applied to organic pollutants. However, the PDS-activation has also been used for bacterial inactivation, such as Water Research, 2020, 176, 115746; Water Research, 2019, 157, 106-118. These studies should be cited and mentioned to show the updated research developments.

2.       In Fig. 1f, only the XPS spectra for Ag(3d) is shown. The full scale XPS spectra and the high-resolution XPS for Ti and O should also be provided and analyzed.

3.       High-resolution TEM showing the crystal lattice (with the d spacing values) of TiO2 and Ag in the Ag/TiO2 composites should be added.

4.       Line 294-295, “LEV underwent partial adsorption, with 15% and 30% adsorbed on TiO2 and Ag/TiO2, respectively (Fig. 2a)”. However, Fig. 2a is the photocatalytic degradation efficacy of LEV. There is no adsorption data in Fig. 2a. Please check and add adsorption data (graphics).

5.       It is known that Ag has antibacterial properties even under dark conditions. Was the photocatalytic inactivation of E. coli due to the intrinsic toxicity of Ag species in the Ag/TiO2? More discussions about the combined effect of Ag toxicity and photocatalysis should be added.

6.       How about the photostability and recyclability? The repeated experiments using the recycled Ag/TiO2 should be conducted. And the possible structure changes of the Ag/TiO2 before and after usage should be investigated by XRD.

Author Response

Please see the attachment. We have prepared a pdf document with the response to the reviewer's comments.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In the manuscript of water-3130110, the authors present a promising work regarding the catalytical removal LSV in a photocatalysis system. I think the concept is good, and the data related to this work is abundant. However, there are some obvious issues need to be addressed before it can be accepted for publication. Enclosed are my comments,

(1) Fluoroquinolones are a class of chemicals. as this study only investigates the degradation of LEV, I suggest to use LEV instead of fluoroquinolone in the title. Results and discussion about the performance and mechanism should focus on LEV not fluoroquinolones in the entire work, such as line 30 in the abstract.  

(2) The first paragraph of the introduction need to be revised. I understand the LEV is difficult to be metabolized by people, its antibiotics property make it a challenge to be degraded in conventional WWTPs. Also, WWTPs need to consider to disinfect the effluent water, typically deactivated the E. coli. I am confused that whether LEV residue is good for E. coli deactivation? Therefore, I suggest to not mention the E. coli, just state the serious issues of antibiotics residue in wastewater may cause the enrichment of ARGs. Therefore, it is important to deeply degrade  Fluoroquinolones such as LEV.

(3) I suggest the author could cite a reference 

Cai, M., LiYang, H., Yang, C., Zhou, Y., WU, H. 2024. Activated Sludge Incineration Ash Derived Fenton-like Catalyst: Preparation and Its Degradation Performance of Methylene Blue. Journal of Inorganic Materials, 39(10), 1135-1142. https://10.15541/jim20230580.

at the introduction section, as it is a fenton-like system which is highly related to this work. And also for https://10.3390/polym15122741. 

(4) Why to set the initial concentration of LEV as 0.05 mmol/L, Whether this concentration is too high?

(5) Figure 1 need to be revised especially for the (e).

(6) need to provide some evidence such as TOC analysis or a discussion that indicated the LEV is completely degraded, not only converted to the intermediates.

(7) About the Figure 6, I think it is too detailed. It is difficult to provide evidence that ROS only destroy the membrane and wall of a cell while UV destroys the DNA Enzymes proteins. Better to revise it to make it no ambiguity.

Hoping these suggestions could help the author improve their manuscript. 

Comments on the Quality of English Language

The quality of English Language in the introduction need to be improved.

Author Response

Please see the attachment. We have prepared a pdf document with the response to the reviewer's comments.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript is interesting as several approaches were used to assess the treatment capability of different photo-processes. However, there are some critical aspects (major revision) that must be considered by the authors to publish the manuscript in this journal.

What is the test water matrix?

UVA intensity is 90 W/m2? Are the authors sure about this value? It is much higher than the usual one and an efficient disinfection by only solar light should be observed (minutes of treatment).

Did the authors measure the Ag Leaching during and after the processes? Leaching has to be measured and considered in these systems as the metals can play a critical role. Can the silver precursor species adsorbed on the oxidative face leach during the process and be the reason for the disinfection improvement shown as Ag is a powerful disinfectant agent?.

A comparison with the commercial, effective and inexpensive TiO2 P25 catalyst has to be included.

Fig 2d. Revise microbiological units and change the icons to make it easier to distinguish the treatments on the graph. Disinfection by only solar light very slow.

The PDS concentration is 0.01 mmol L-1? Or 0.01 mol L-1?

AA activity removal was performed replicated? There are not statistics in the graphic and it is a measurement with high error associated.

 

Figure 3b. Are the authors sure that radicals can be generated in the dark by the interaction between TiO2 and PDS? TiO2 without light is inert.

Author Response

Please see the attachment. We have prepared a pdf document with the response to the reviewer's comments.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

All the issues have been clarified, and the manuscript can be accepted in the current form.

Author Response

Thanks for the revision

Reviewer 2 Report

Comments and Suggestions for Authors

After this time of revision, the authors have well addressed most of my comments. The quality of this manuscript improved significantly. However, I still have a little suggestions on its current introduction.

In order to save the time and human efforts in reviewing, I suggest the author could consider to revise the 1st and 2nd paragraphs of the introduction as follows,

The presence of antibiotics in aquatic environments poses a significant risk by potentially causing irreversible long-term changes in bacterial genomes, leading to the development of antibiotic-resistant microorganisms—a serious public health concern. Levofloxacin (LEV), a widely used antibiotic for treating various bacterial infections, exemplifies this issue. After consumption, approximately 87% of LEV is excreted unchanged, eventually reaching municipal wastewater treatment plants (WWTPs). However, due to its strong antimicrobial properties, LEV resists degradation by conventional WWTP methods, highlighting the need for more effective treatments to eliminate it from wastewater.

In parallel, Escherichia coli (E. coli) serves as a universal indicator of microbiological water contamination and is commonly detected in wastewater and WWTP effluents. The limitations of classical WWTP treatments in effectively addressing E. coli contamination underscore the necessity for alternative approaches. These could include advanced treatments at primary pollution sources, such as hospital wastewater or even the urine from patients harboring such bacteria, to mitigate the spread of resistant microorganisms and safeguard public health. Therefore, seeking effective ways to deeply eliminate the environmental risk caused by LEV and microbial contaminants is of great importance.

I think this would be more readable than the previous version.

Comments on the Quality of English Language

All good.

Considering about revising the introduction. Remember to go through the entire manuscript before submitting new version. 

Author Response

Thanks for the suggestion. We have modified the paragraphs as the reviewer has rewritten.

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript was improved and can be published.

 

Author Response

Thanks for the revision