Review Reports - Effect of Fe(II)-Activated Peroxymonosulfate (PMS) on the Performance of Ultrafiltration (UF) Process for Secondary Effluent Treatment and Reuse

Round 1

Reviewer 1 Report

The article may be considered for acceptance, provided that the authors consider the following comments and recommendations:

Line 66: “Therefore, many studies have turned their attention to pretreatment of membranes.” Do the authors mean pre-treatment of the influent before membrane filtration?
Lines 94-95: “… the fouling mechanism was explored by Electron paramagnetic resonance (EPR), …” The mechanism of oxidation can be investigated using electron paramagnetic resonance, but not fouling. Please revise.
Lines 126-128: “The dosage of Fe(II)/PMS used in the Fe(II)-126 activated PMS experiment included: 0/0, 0/30, 0/60, 30/30, 60/60, 120/120, 15/60, 30/60, 127 90/60, 120/60, 60/15, 60/30, 60/90, 60/120 μmol/L.” Instead of “μmol/L“ should be “μM/μM”. Please correct.
Please provide data on the main parameters of the real sample used in this study, for example, in the form of a table with the main characteristics such as pH, ionic composition, organics, etc.
Lines 266-268: “Compared with the control group, the TOC removal rates of the second to eighth groups were 4.2%, 13.0%, 14.2%, 6.5%, 21.4%, 29.3%, and 35.8%, respectively.” It is not clear which data relate to which treatment process/sample. Rewrite or remove this sentence.
Lines 273-275: “Compared with the effluent of the control group, the UV254 values of the remaining groups decreased by 3.7%, 12.2%, 23.4%, 6.4%, 31.9%, 46.3%, and 49.5%, respectively…” It is not clear which data relate to which treatment process/sample. Rewrite or remove this sentence.
Lines 291-294: “As shown in Figure 3(b), detecting effluent after pretreatment and ultrafiltration, the protein concentrations of the second to eighth groups reduced by 5.8%, 13.6%, 15.6%, 19.5%, 29.2%, 39.0%, and polysaccharides reduced by 44.8%, 36.4%, 42.4%, 35.3%, 39.9%, 49.6%, 58.0%, respectively, compared with the control group.” It is not clear which data relate to which treatment process/sample. Rewrite or remove this sentence.
Lines 346-348: “Figure 3(c) reveals that the TN concentrations leveled off, and that for the eight groups of membranes were 16.20, 16.19, 16.07, 15.93, 16.16, 16.07, 15.86, and 15.78 mg/L, respectively.” It is not clear which data relate to which treatment process/sample. Rewrite or remove this sentence.
Lines 441-443: “The total resistance values of the 8 groups were 4.49×1011 m-1, 4.34×1011 m-1, 3.16×1011 m-1, 2.99×1011 m-1, 3.46×1011 m-1, 2.98×1011 m-1, 2.77×1011 m-1, 2.21×1011 m-1, respectively.” It is not clear which data relate to which treatment process/sample. Rewrite or remove this sentence.

Author Response

The article may be considered for acceptance, provided that the authors consider the following comments and recommendations:

Re: Thank you very much for the reviewer’s comments on this manuscript. The questions you raised for this manuscript are the most important issues in our research and writing process, and we highly appreciate your insightful comments and helpful suggestions. We have carefully considered the opinions of and made amendments on this basis. The following will respond to your questions one by one.

1* Line 66: “Therefore, many studies have turned their attention to pretreatment of membranes.” Do the authors mean pre-treatment of the influent before membrane filtration?

Re: Thanks for your question. The “pretreatment of membranes” mentioned in this manuscript all refer to the pre-membrane water quality optimization means, such as coagulation, oxidation, adsorption, etc., to improve the water quality of the membrane influent [1].

2* Lines 94-95: “... the fouling mechanism was explored by Electron paramagnetic resonance (EPR)....” The mechanism of oxidation can be investigated using electron paramagnetic resonance, but not fouling. Please revise.

Re: Thanks for the insightful suggestion. The authors have already made revisions and annotations in the revised manuscript (Line 94).

3* Lines 126-128: “The dosage of Fe(II)/PMS used in the Fe(II)-PMS activated PMS experiment included: 0/0, 0/30, 0/60, 30/30, 60/60, 120/120, 15/60, 30/60, 90/60, 120/60, 60/15, 60/30, 60/90, 60/120 umol/L.” Instead of “umol/L” should be “uM/uM”. Please correct.

Re: Thanks for the helpful suggestions. The authors have already made revisions and annotations in the revised manuscript (Line 129).

4* Please provide data on the main parameters of the real sample used in this study, for example, in the form of a table with the main characteristics such as pH, ionic composition, organics, etc.

Re: Thanks for the comment. We have made additions and improvements based on your suggestions and added information on raw water quality in Table S1 of the supporting information.

Table S1 Characteristics of secondary effluent quality.

Water quality parameters	Units	Ranges of concentration	Mean values
TOC	mg/L	8-10	9.12
BOD₅	mg/L	4-6	5
TN	mg/L	15-20	16.4
TP	mg/L	0.6-0.8	0.7
Turbidity	NTU	2-5	3.6
Temperature	℃	18-22	20
pH	-	5-7	6.6

5* Lines 266-268: “Compared with the control group, the TOC removal rates of the second to eighth groups were 4.2%, 13.0%, 14.2%, 6.5%, 21.4%, 29.3%, and 35.8%, respectively.” It is not clear which data relate to which treatment process/sample. Rewrite or remove this sentence.

Re: Thanks for the comments. To facilitate the reader's understanding, the authors have explained the dose setting for each group in detail in the revised manuscript (Lines 264-267).

6* Lines 273-275: “Compared with the effluent of the control group, the UV₂₅₄ values of the remaining groups decreased by 3.7%, 12.2%, 23.4%, 6.4%, 31.9%, 46.3%, and 49.5%, respectively...” It is not clear which data relate to which treatment process/sample. Rewrite or remove this sentence.

Re: Thanks for the comments. To facilitate the reader's understanding, the authors have explained the dose setting for each group in detail in the revised manuscript (Lines 264-267).

7* Lines 291-294: “As shown in Figure 3(b), detecting effluent after pretreatment and ultrafiltration, the protein concentrations of the second to eighth groups reduced by 5.8%, 13.6%, 15.6%, 19.5%, 29.2%, 39.0%, and polysaccharides reduced by 44.8%, 36.4%, 42.4%, 35.3%, 39.9%, 49.6%, 58.0%, respectively, compared with the control group.” It is not clear which data relate to which treatment process/sample. Rewrite or remove this sentence.

Re: Thanks for the comments. To facilitate the reader's understanding, the authors have explained the dose setting for each group in detail in the revised manuscript (Lines 264-267).

8* Lines 346-348: “Figure 3(c) reveals that the TN concentrations leveled off, and that for the eight groups of membranes were 16.20, 16.19, 16.07, 15.93, 16.16, 16.07, 15.86, and 15.78 mg/L, respectively.” It is not clear which data relate to which treatment process/sample. Rewrite or remove this sentence.

Re: Thanks for the comments. To facilitate the reader's understanding, the authors have explained the dose setting for each group in detail in the revised manuscript (Lines 264-267).

9* Lines 441-443: “The total resistance values of the 8 groups were 4.49×10¹¹ m^-1, 4.34×10¹¹m^-1, 3.16×10¹¹ m^-1, 2.99×10¹¹ m^-1, 3.46×10¹¹ m^-1, 2.98×10¹¹ m^-1, 2.77×10¹¹ m^-1, 2.21×10¹¹ m^-1, respectively.” It is not clear which data relate to which treatment process/sample. Rewrite or remove this sentence.

Re: Thanks for the comments. To facilitate the reader's understanding, the authors have explained the dose setting for each group in detail in the revised manuscript (Lines 446-449).

References:

Gao, W., Liang, H., Ma, J., Han, M., Chen, Z.-l., Han, Z.-s.,Li, G.-b. Membrane fouling control in ultrafiltration technology for drinking water production: A review. Desalination 2011, 272, 1-8.

Reviewer 2 Report

The manuscript has been improved according to my comments, hence, I recommend it for publication.

Author Response

The manuscript has been improved according to my comments, hence, I recommend it for publication.

Re: Thank you very much for your appreciation of our manuscript. Your opinions are the greatest encouragement to our work.

Reviewer 3 Report

Ultrafiltration (UF) is promising process for the treatment of secondary effluent of WWTP. But, the efficiency of UF is limited by the membrane fouling. Membrane fouling shortens the lifetime of membranes, limits the capacity of UF modules and has effect on the pollutant removal efficiency, as well.

The application of PMS coagulation and oxidation processes before UF can mitigate the fouling. MS has a specific research focus on the effects of Fe(II)/PM ratio on the removal efficiency and fouling behaviour, as well. Therefore, the topic of the manuscript can be considered as interesting for the readers.

The manuscript is generally well written with a logic structure. Introduction summarizes well the relevance of the study, and the background of the research. The specific research motivations and the main aims of the research are clearly given. Key words are well defined.

The applied methods are adequate to the aims/focus of the research. Materials and methods are given clearly and in details (some section contains unnecessary information, please see my specific comment).

The MS contains interesting results that are valuable not just for the science but also for the practice. removal efficiency was characterized by non-specific indicators (TOC, UV254) and by macromolecular components/TN/TP, as well. Investigation of membrane morphology and membrane fouling mechanisms can provide useful information for the practice. Experimental results are discussed in details with relevant references.

Comments, suggestions:

It is not clear how was the Fe(II)/PMS dosage levels are defined (based on preliminary experiments, or using preliminary experiences form references)?

In my opinion, unnecessary information is given in line 142-147 (unnecessary methodology details).

If the authors decided to give the ‘background’ of membrane fouling modelling please give this information in the Introduction section (see line 207-220).

Please improve the visibility/quality of Figure 3 (mainly the axis labels).

I suggest to the authors to give a brief summary on the practical applicability and the possibilities for scaling-up the process compare to the other fouling mitigation methods.

Author Response

The application of PMS coagulation and oxidation processes before UF can mitigate the fouling. MS has a specific research focus on the effects of Fe(II)/PMS ratio on the removal efficiency and fouling behaviour, as well. Therefore, the topic of the manuscript can be considered as interesting for the readers.

The MS contains interesting results that are valuable not just for the science but also for the practice. removal efficiency was characterized by non-specific indicators (TOC, UV₂₅₄) and by macromolecular components/TN/TP, as well. Investigation of membrane morphology and membrane fouling mechanisms can provide useful information for the practice. Experimental results are discussed in details with relevant references.

Re: Thanks very much for the reviewer’s positive evaluations. We highly appreciate the reviewer’s insightful comments and helpful suggestions, which greatly improve the quality of the manuscript. We have tried our best to consider the reviewer’s comments carefully and revised the manuscript accordingly.

Comments, suggestions:

1* It is not clear how was the Fe(II)/PMS dosage levels are defined (based on preliminary experiments, or using preliminary experiences form references)?

Re: Thanks for the helpful comments. The setting of the dosage ratios of the experiment were based on the reference of other experiments [1, 2], and the corresponding preliminary experimental evaluations were carried out before this research.

2* In my opinion, unnecessary information is given in line 142-147 (unnecessary methodology details.

Re: Thanks for the comment. We have fully considered your comments and made corresponding deletions in the revised manuscript (Lines 146-150).

3* If the authors decided to give the ‘background’ of membrane fouling modelling please give this information in the Introduction section (see line 207-220).

Re: Thank you for your helpful suggestions. The authors believed that the Introduction focused on the detailed description of the membrane technology and the Fe(II)/PMS pretreatment method applied in the manuscript. The fitting of the fouling model did not belong to the category of “background”, and the research of other scholars also tended to think of it as a “method” [3, 4].

4* Please improve the visibility/quality of Figure 3 (mainly the axis labels).

Re: Sorry for our carelessness. The figure quality in the revised manuscript has been improved to provide clearer and more useful information.

5* I suggest to the authors to give a brief summary on the practical applicability and the possibilities for scaling-up the process compare to the other fouling mitigation methods.

Re: Thanks for your insightful comments. Fe(II)-activated PMS process has the advantages of more efficient removal of organic pollutants, less dosage, and relatively low cost as a pretreatment method of membrane technology. The two synergistically have the dual functions of coagulation and oxidation. Compared with single coagulation and single oxidation, it showed better performance in reducing reversible and irreversible fouling [4]. The Conclusions in the manuscript have been reflected accordingly (Lines 518-519), and at the same time, we have also taken your comments into consideration and made supplements in the Conclusions accordingly (Lines 533-534).

References:

Cheng, X., Liang, H., Ding, A., Tang, X., Liu, B., Zhu, X., Gan, Z., Wu, D.,Li, G. Ferrous iron/peroxymonosulfate oxidation as a pretreatment for ceramic ultrafiltration membrane: Control of natural organic matter fouling and degradation of atrazine. Water Res 2017, 113, 32-41.
Cheng, X., Liang, H., Ding, A., Zhu, X., Tang, X., Gan, Z., Xing, J., Wu, D.,Li, G. Application of Fe(II)/peroxymonosulfate for improving ultrafiltration membrane performance in surface water treatment: Comparison with coagulation and ozonation. Water Res 2017, 124, 298-307.
Shen, Y., Zhao, W., Xiao, K.,Huang, X. A systematic insight into fouling propensity of soluble microbial products in membrane bioreactors based on hydrophobic interaction and size exclusion. J Membrane Sci 2010, 346, 187-193.
Bowen, W. R., Calvo, J. I.,Hernández, A. Steps of membrane blocking in flux decline during protein microfiltration. J Membrane Sci 1995, 101, 153-165.