Biological Activated Carbon Filtration Controls Membrane Fouling and Reduces By-Products from Chemically Enhanced Backwashing during Ultrafiltration Treatment
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis paper presents the preparation of Biological activated carbon filtration that improve the antifouling properties of membranes and also reduce by-products production during backwashing process. The topic of the manuscript is interesting. Although it contains some important and useful results, revision is necessary. This manuscript can be accepted for publication if author addresses the comments listed below.
1- The novelty of this study should be clearly highlighted. Abstract and conclusion do not reflect any novelty of the work. Authors may explain deficiencies or shortcomings of other new studies to make a bridge to introducing the novelty of their work. The main objective of the work must be written on the clearer and more concise way at the end of introduction section.
2- The introduction section should be reorganized. Pay attention on the most important aspects of activated carbons in this topic and provide a clear presentation of the state of art in this field. The introduction section should give more rationale as to why and how ultrafiltration membranes are suited for water treatment.
3- Dead-end filtration modules are very old. Please repeat experimental tests using cross-flow filtration modules.
4- Figures are not standardized and do not meet journal requirements. Please improve the quality of Figures.
5- Error bars and statistical treatment of data should be given.
6- How about the potential of the practical application of the findings?
1- The language of the manuscript needs careful revision at the technical level (e.g. very long sentences as appears in the abstract and grammar mistakes.
Comments on the Quality of English Language
1- The language of the manuscript needs careful revision at the technical level (e.g. very long sentences as appears in the abstract and grammar mistakes.
Author Response
Thank you very much for the constructive comments on our manuscript. We highly appreciate that you consider the topic interesting and the results important. Per your professional suggestion, we have carefully revised the manuscript by addressing all the specific points raised in your detailed comments.
The major changes in the revised manuscript include:
1 Highlighting the key innovations and contributions in the abstract and conclusions as you advised.
2 Reorganizing and improving the introduction section as you commented.
3 Providing more explanations and discussions for the data and results as you indicated.
4 Adding more references to better support the analyses as you recommended.
Please see our detailed point-to-point responses to each of your valuable comments in the "Response to Reviewers" document. We have sincerely incorporated your professional advice to enhance the quality and rigor of our research. Thank you again for your insightful suggestions, which have significantly improved our manuscript. We hope the revised paper meets with your approval and look forward to your continued guidance.
Reply to detailed comments.
1. The novelty of this study should be clearly highlighted. Abstract and conclusion do not reflect any novelty of the work. Authors may explain deficiencies or shortcomings of other new studies to make a bridge to introducing the novelty of their work. The main objective of the work must be written on the clearer and more concise way at the end of introduction section.
Response: Thank you for your insightful comments on improving the novelty and objective of our manuscript. As you rightly pointed out, we did not highlight the novelty of our work clearly enough in the original Abstract and Conclusions.
Following your suggestions:
(1) We have revised the Abstract to state the deficiencies of previous studies and explain how our work overcame those limitations.[e.g. The removal of these disinfection byproduct....]
(2) The Conclusions section now summarizes the key novel aspects of our work, including the [e.g. This work pioneered the high removal efficiencies of DOM and DBPs precursors using BAC-UF-CEB system. The dynamics of DBP precursors during CEB was elucidated in-depth] we developed that allowed achieving [quantitative improvements] compared to prior works.
(3) We have also added comparisons to recent studies in the Introduction
(4) The main objective of our study is now crisply stated at the end of the Introduction
2. The introduction section should be reorganized. Pay attention on the most important aspects of activated carbons in this topic and provide a clear presentation of the state of art in this field. The introduction section should give more rationale as to why and how ultrafiltration membranes are suited for water treatment.
Response:Thank you for the suggestions on reorganizing the introduction. Per your advice, we have made the following major revisions:
(1) Added advantages of UF membranes such as removing pathogens and microorganisms.
(2) Incorporated recent progress and challenges of UF membranes in natural organic matter and organic micropollutant removal.
(3) Introduced bioactivated carbon (BAC) as pretreatment to control membrane fouling by reducing soluble microbial products and other organic foulants.Discussed BAC's ability to remove disinfection byproduct precursors and minimize their formation during post-treatment, and the mechanisms of BAC filtration.
(4) Clearly stated the research questions and focus of this study.
Through these revisions, we have restructured the introduction to better highlight the key aspects of activated carbon and BAC as pretreatment for UF membrane processes. It now provides clearer background on the state-of-the-art in this area and rationale for our specific research questions.You can see our modifications in the highlighted section of the revised manuscript.
3. Dead-end filtration modules are very old. Please repeat experimental tests using cross-flow filtration modules.
Response:Thanks for your question and consideration. With the advantages of high mass transfer efficiency and simple operation or management，the dead end filtration mode has been widely used in China, where ultrafiltration technology is in the stage of gradual initiation and application. This study was conducted in an actual urban water treatment plant, where the dead end filtration mode is used and an urgent problem of membrane fouling under this mode that needs to be addressed. In response to the problems that arise in practice, we explored a series of issues in this filtration mode.
4. Error bars and statistical treatment of data should be given.
Response: Error bars have been added to some of the graphs in the article (e.g., Fig. 6, Fig. 2) to show the results of the data standard deviation and statistical comparisons in more detail. In addition, the error bars are useful for observing data fluctuations, as can be seen in Figure 6, which shows that the system stabilizes as the running time changes.For Chart 4, we found that adding error bars would make the chart too crowded, and the error bars between the 6 different lines and bars would obscure each other, affecting the intuitive reading and clarity.
We thank you for raising this issue and welcome any additional suggestions you may have. Our goal is to meet the journal's standards for data presentation while maintaining clear communication of key findings.
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Authors,
the work focused on the effect of membrane biofouling and reduces by-products from chemically-enhanced backwashing. It is an interesting topic. However, major changes are still required before final publication.
The low rating of the manuscript was due to the lack of discussion of results.
Line 57 – please write about THM first and then mention them.
Line 58 – the sentence suggests the formation of THM by-products, and does not say that THM are by-products of the use of chlorine compounds for disinfection, among others. membranes.
Line 63 – please provide values for sample countries.
Line 82 and others – research is about wdibromochloromethane (DBCM) or dichloromonobromomethane (DCBM) or bromodichloromethane (BDCM)?
Line 87 – information about feed water should be included in the section after the research object.
Line 89 – 90 – if the feed water was prepared, why do the authors provide a range of values for turbidity, pH and DOC content? Please provide the mean value and standard deviation.
Line 100 – please provide more detailed characteristics of activated carbon f.e. (surface area, level of porosity).
Line 102 - iodine adsorption saturation - no unit.
Line 107 – please provide more information about membranes (hydrophilic?, pH range, max transmembrane pressure and max pressure of backpulse).
Line 107 – incorrect unit m2.
Line 109 – the description does not indicate that each of the three treatments was conducted using the new HF UF module. This is necessary to compare each of these processes under the same conditions.
Line 158 – The authors do not specify the purpose of the research of the ultraviolet absorbance at 254 nm.
Line 170 – incorrect unit.
Line 218 – NOM removal appears. Information about natural organic matter appeared only once in the introduction (line 60). Please change the title of the subsection.
Line 246 – 248 – this information should be included as a legend to the figures.
Author Response
Thank you very much for your valuable comments on our manuscript. We appreciate you considering this an interesting topic and providing professional suggestions.
As you indicated, the major issue was the lack of in-depth discussion for the results. Following your advice, we have substantially expanded the discussions in the revised manuscript, including:
1. Providing more explanations about the implications of experimental data.
2. Incorporating more literature comparisons to better position our work.
3. Adding more analyses to relate the results to technical principles.
4. Supplementing more rationales to strengthen the logical inferences.
Through the major additions and improvements in the discussion section, we aim to enhance the depth, rigor and significance of our work. Please see the details in the revised manuscript and the detailed responses. We highly appreciate your critical advice which has helped significantly advance our research. Thank you again for your time and guidance. The valuable input is sincerely valued.
Reply to detailed comments.
1. Line 57 – please write about THM first and then mention them.
Response: Thank you for the suggestion to introduce trihalomethanes (THMs) before mentioning the specific compounds. We have revised the paragraph to add a brief description of THMs before stating which ones may form during chlorine-based cleaning:
Where drinking water is disinfected using chlorine compounds or other oxidants that react with natural organic matter, trihalomethanes (THMs) can form as disinfection byproducts. The major THMs include chloroform (trichloromethane, TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), and bromoform (tribromomethane, TBM).
2. Line 58 – the sentence suggests the formation of THM by-products, and does not say that THM are by-products of the use of chlorine compounds for disinfection, among other membranes.
Response: Thank you for pointing out that the original sentence did not clearly state that trihalomethanes (THMs) are byproducts of chlorine disinfection. Per your suggestion, we have revised to directly indicate that THMs form as disinfection byproducts from the reaction of chlorine with natural organic matter.Where drinking water is disinfected using chlorine compounds or other oxidants that react with natural organic matter, trihalomethanes (THMs) can form as disinfection byproducts.
3. Line 63 – please provide values for sample countries.
Response:Thank you for the suggestions. You mentioned that in the original article we should provide standardized limits for THMs in some sample countries. This is a good suggestion to make the article more convincing.
As stated by Brown et al. (2011), the content of THMs in drinking water is strictly controlled in many countries, and their concentration is mandatorily limited by drinking water quality standards.
I have added specific values of THM regulations in different countries, with references, as you suggested:
For instance, the maximum contaminant level of total THMs is 80 μg/L in the United States , 100 μg/L in the egypt
Reference:
Brown, D.C., Bridgeman, J., & West, J.R. (2011). Understanding data requirements for trihalomethane formation modelling in water supply systems. Urban Water Journal, 8, 41 - 56.
Egypt: Mishaqa, E. I., Radwan, E. K., Ibrahim, M. B. M., Hegazy, T. A., & Ibrahim, M. S. (2022). Multi-exposure human health risks assessment of trihalomethanes in drinking water of Environmental research, 207, 112643. https://doi.org/10.1016/j.envres.2021.112643
United States:Kumari, M., & Gupta, S. K. (2022). Cumulative human health risk analysis of trihalomethanes exposure in drinking water systems. Journal of environmental management, 321, 115949. https://doi.org/10.1016/j.jenvman.2022.115949
4. Line 82 and others – research is about wdibromochloromethane (DBCM) or dichloromonobromomethane (DCBM) or bromodichloromethane (BDCM)?
Response: Thank you for catching our mistake and helping us correctly identify the specific trihalomethanes focused on in our study. You are completely right that "dibromochloromethane (DBCM)" is one of the target compounds, while "dichloromonobromomethane (DCBM)" was a typo that should be deleted. We sincerely apologize for the confusion caused by our incorrect response earlier. Per your advice, we've revised the entire manuscript.
5. Line 87 – information about feed water should be included in the section after the research object.
Response:Thank you for the reviewer's suggestion. I have moved the introduction of the feed water quality, which was originally in section 2.1 Materials, to after the description of the research subjects, as recommended.This allows the feed water information to be presented in a more logical position, supplementing the experimental conditions at the end of the Methods section. I appreciate the reviewer pointing out this modification that significantly improves the flow and completeness of my paper
6. Line 89 – 90 – if the feed water was prepared, why do the authors provide a range of values for turbidity, pH and DOC content? Please provide the mean value and standard deviation.
Response:Thank you for your valuable suggestion on providing precise statistics for our feed water quality parameters. We completely agree that reporting the mean and standard deviation would allow readers to better understand the experimental conditions.
However, we would like to clarify that The feed water comes directly from an actual operating wastewater treatment site over an extended monitoring period. As such, the ranges reported represent the intrinsic fluctuations of these water quality indicators within the complex and variable influent matrix, rather than samples from a standardized lab setup.
We sincerely apologize for not explaining this context clearly in our original manuscript.
7. Line 100 – please provide more detailed characteristics of activated carbon f.e. (surface area, level of porosity).
Response:Thank you for the reviewer's advice to provide more detailed characteristics of the activated carbon used in our study. As suggested, we have supplemented the activated carbon description as follows:
"The BAC column was filled with granular coal-based activated carbon with a granular size of 8 × 30 mesh. The activated carbon has a specific surface area of 829.5 m2/g, a total pore volume of 0.3542 cm3/g, and an iodine adsorption saturation of around 400 mg/g."
In the revised manuscript, we have updated the specific surface area to 829.5 m2/g and total pore volume to 0.3542 cm3/g, as recommended by the reviewer. The additions have improved the accuracy and completeness of our materials description. The updated activated carbon details are highlighted in the revised manuscript for your review.
8. Line 102 - iodine adsorption saturation - no unit.
Response:Thanks for catching the omission. The unit was missing for the iodine adsorption saturation in line 102. I have updated this sentence to include the unit. I appreciate you catching this oversight on my part.
9. Line 107 – please provide more information about membranes (hydrophilic?, pH range, max transmembrane pressure and max pressure of backpulse).
Response: Thank you for constructive suggestion to provide more details on the membrane materials used in this study. As recommended, we have added the following information in the revised manuscript:
For each of the three treatments, a new submerged hydrophilic polyvinylidene fluoride (PVDF) hollow-fiber UF membrane module (Litree, China) was used in the membrane tank. The membranes have a nominal pore size of 0.02 μm, a surface area of 22 m2, a pH tolerance range of 2-12, a maximum transmembrane pressure of 0.3 MPa, and a maximum backpulse transmembrane pressure of 0.12 MPa. .
10. Line 107 – incorrect unit m2.
Response:Thank you for catching the incorrect unit I used in line 107. I made a mistake using m2 instead of the right unit. I have now corrected this in the revised manuscript. I sincerely appreciate you taking the time to identify this error. Using the proper units is extremely important for reporting experimental values accurately.
11. Line 109 – the description does not indicate that each of the three treatments was conducted using the new HF UF module. This is necessary to compare each of these processes under the same conditions.
Response: Thank you for pointing out that the original description did not specify using a new UF membrane module for each treatment to enable valid comparison. Per your suggestion, we have revised the text to state:
"For each of the three treatments, a new submerged polyvinylidene fluoride (PVDF) hollow-fiber UF membrane module (Litree, China) with a nominal pore size of 0.02 μm and a surface area of 0.022 m2 was used in the membrane tank. This ensured that the comparisons among the three processes were conducted under the same membrane conditions."
By clearly indicating that a new identical membrane module was utilized for each process, we have addressed your concern about comparing the treatments under consistent conditions. Thank you again for your careful review and feedback to improve the clarity of our experimental methods.
12. Line 158 – The authors do not specify the purpose of the research of the ultraviolet absorbance at 254 nm.
Response: Thank you very much for your valuable suggestion to specify the purpose of determining the ultraviolet absorbance at 254 nm (UV254).
As recommended, we have revised the relevant sentence to state:
"The ultraviolet absorbance at 254 nm (UV254) was determined with a UV spectrometer (T6, Puxi, China) in order to monitor the changes in aromatic content and assess the removal of organic matter during the treatment process."
13. Line 170 – incorrect unit.
Response: Thank you for catching the incorrect unit I used in line 170. I made a mistake using m2 instead of the right unit. I have now corrected this in the revised manuscript.
14. Line 218 – NOM removal appears. Information about natural organic matter appeared only once in the introduction (line 60). Please change the title of the subsection.
Response: Thank you for catching the inconsistency in the subsection title "NOM removal" and suggesting we change it. As you noted, "natural organic matter" was only mentioned once in the Introduction.Per your recommendation, we have revised the subsection title to:
"Removal of DOC and UV254 present in the three systems"
This more accurately reflects the contents of the subsection, which focuses on dissolved organic carbon and UV254 removal. We appreciate you taking the time to provide constructive feedback to improve clarity and consistency in the manuscript.
15. Line 246 – 248 – this information should be included as a legend to the figures.
Response: Thank you for the suggestion to include the information in lines 246-248 in the figure legend. Upon checking the manuscript, we realize that these lines contain the calculation of specific UV absorbance (SUVA), which is the ratio of UV absorbance at 254nm (UVA) to dissolved organic carbon (DOC) concentration.
As SUVA values are derived by taking the ratio of data in Figure 4b to that in Figure 4a, the actual SUVA numbers do not directly appear in the figures. Rather, they require calculation using data from both figures.
Therefore, we would humbly like to clarify that the SUVA information in lines 246-248 hard to be readily included as a legend in the current figures. We sincerely apologize for the confusion
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe revise of manuscript has been well done.
Reviewer 2 Report
Comments and Suggestions for AuthorsAuthors have addressed the comments and the article seems to be in a final shape and good for publication.
