Effect of Electrochemical Pre-Oxidation for Mitigating Ultrafiltration Membrane Fouling Caused by Extracellular Organic Matter
Round 1
Reviewer 1 Report
The manuscript contains relevant and interesting results on mitigation UF fouling from algae-derived organic matter. The article has the adequate structure and gives enough information on the introduction and the material and methods. Results are well presented and discussed. The references used are updated as well.
Author Response
Thanks for the kindly comment from the reviewer.
Reviewer 2 Report
This study evaluated the performance of electrochemical oxidation as pretreatment to control the fouling issue of membrane process caused by extracellular organic matter. Though the study reported interesting finding, there are a few major aspects that need to be improved before it can be considered for publication.
1. The abstract should include data (findings) and discussion.
2. Clarification is required for methodology. The feed water for membrane filtration was taken from the electrochemically-treated water?
3. Incomplete sentence in results and discussion (line 188).
4. Though the discussion was satisfactorily, references must be cited to support the claims made on the observation from this study.
5. It is suggested to provide membrane autopsy results to support the fouling explanation.
The manuscript requires proofreading to improve the language quality. Avoid writing long sentences (e.g., first sentence of abstract).
Author Response
This study evaluated the performance of electrochemical oxidation as pretreatment to control the fouling issue of membrane process caused by extracellular organic matter. Though the study reported interesting finding, there are a few major aspects that need to be improved before it can be considered for publication.
Response: Thanks for the patiently and meticulous review from the reviewer. This study focused on the membrane fouling control strategy of electrochemical pre-oxidation for excellular organic matter of algae-laden water. To the best of our knowledge, the pretreatment of electrochemical pre-oxidation for mitigating ultrafiltration membrane fouling caused by extracellular organic matter had not been reported before. To improve the quality of this paper, the abstract was revised. Furthermore, we carefully checked the whole paper to avoid grammatical errors and better reconstruct sentences as much as possible. Also the figures were revised for clear representation. Hope our revision could meet the standard of the journal.
- The abstract should include data (findings) and discussion.
Response: Thanks for the review from the reviewer. We revised the abstract to include data and discussion from this study.
- Clarification is required for methodology. The feed water for membrane filtration was taken from the electrochemically-treated water?
Response: Thanks for the review from the reviewer. The samples after different duration of electrochemically-treatment was directly filtrated by the membrane.
- Incomplete sentence in results and discussion (line 188).
Response: Thanks for the review from the reviewer. The incomplete sentence was revised to “This may because that small molecular organics generated at 10 min had higher potential to penetrate in or adsorb onto the membrane.”
- Though the discussion was satisfactorily, references must be cited to support the claims made on the observation from this study.
Response: Thanks for the review from the reviewer. We had added references to support the claims made on the observation from this study.
- It is suggested to provide membrane autopsy results to support the fouling explanation.
Response: Thanks for the review from the reviewer. In this study, we employed membrane fitration flux curve, fouling modeling, organic property analysis to investigate the fouling mitigation performance and mechanism of BDD anodizing pretreatment for extracellular organic matters. In our future study, we are pleased to utilize more methods such as autopsy for the fouling explanation.
Reviewer 3 Report
1. There was no up-to-date information on the current status of the electrochemical pretreatment of the membrane process, especially ultrafiltration.
2. Why BDD is used, as it is expensive compared to all other electrode materials.
3. The efficiency of electrochemical oxidation to degrade and mineralize the organic pollutants is well known with boron-doped diamond (BDD) electrodes. I don’t see any novelty in this work. The emerging trends are using membranes as electrodes and degrading minimizing the fouling formation (there is growing research on electroconductive membrane development-need to add to the discussions from this area of literature).
4. Comparison to other related studies should be included in terms of flux and removal efficiency should be discussed. In the end, the comparison of energy consumption needs to be discussed.
5. Line 262-264 “When pre-oxidation was employed, the zeta potential of the EOM solution started to decline, which indicate that the solution tends to unstable when BDD anodizing utilized. And with longer oxidation duration, the decline of zeta potential was more significant.” Why does it happen? What is the mechanism? Need valid information with reference to the relationship between zeta potential and solution stability.
6. MCLR abbreviation is missing.
7. The modeling part is not explained in the appropriate way. What is the importance of modeling and fitting curves (Figure 5), how does it help this scope of the paper?
Language can be improved.
Author Response
- There was no up-to-date information on the current status of the electrochemical pretreatment of the membrane process, especially ultrafiltration.
Response: Thanks for the review from the reviewer. The study of electrochemical pretreatment for ultrafiltration fouling mitigation was rarely reported by previous literature. Our research group had one related reference on this research filed (Liu, Bin, et al. "Ultrafiltration pre-oxidation by boron-doped diamond anode for algae-laden water treatment: membrane fouling mitigation, interface characteristics and cake layer organic release." Water Research 187 (2020): 116435.).
- Why BDD is used, as it is expensive compared to all other electrode materials.
Response: Thanks for the review from the reviewer. The BDD anode was with many merits. BDD electrode is a superior catalytic electrode material with high oxygen evolution potential, and was usually preferred as the non-active anode due to its stability and efficiency. Besides, the BDD anodizing shows high degradation and mineralization effect under wide pH range. Therefore, we employed BDD anodizing as UF pretreatment.
- The efficiency of electrochemical oxidation to degrade and mineralize the organic pollutants is well known with boron-doped diamond (BDD) electrodes. I don’t see any novelty in this work. The emerging trends are using membranes as electrodes and degrading minimizing the fouling formation (there is growing research on electroconductive membrane development-need to add to the discussions from this area of literature).
Response: Thanks for the review from the reviewer. We can understand the reviewer's point of view, and indeed the current research on electroconductive membrane is more hot. However, in this work, we evaluated the effect and mechanism of BDD electrode oxidation as a pretreatment on fouling mitigation in the process of ultrafiltration treatment of EOM. In fact, this is a good supplement to the technology of electrochemical oxidation coupled membrane separation, and also can provide new perspectives for the industry.
- Comparison to other related studies should be included in terms of flux and removal efficiency should be discussed. In the end, the comparison of energy consumption needs to be discussed.
Response: Thanks for the review from the reviewer. The comparison and citation to related studies was added in the result and discussion. At present, our work is still in the small-scale test stage, and its energy consumption is quite different from that of large-scale applications. When we use larger-scale reactors (such as 10 tons per hour) in the future, we will analyze the energy consumption as one of the focuses of our research.
- Line 262-264 “When pre-oxidation was employed, the zeta potential of the EOM solution started to decline, which indicate that the solution tends to unstable when BDD anodizing utilized. And with longer oxidation duration, the decline of zeta potential was more significant.” Why does it happen? What is the mechanism? Need valid information with reference to the relationship between zeta potential and solution stability.
Response: Thanks for the review from the reviewer. The zeta potential of the water samples represents the the state of the substance in the water. In fact, many of our previous studies had similar findings. As the oxidation strength increases, the zeta potential of the solution decreases gradually (Cheng, Xiaoxiang, et al. "Integrated ferrate and calcium sulfite to treat algae-laden water for controlling ultrafiltration membrane fouling: High-efficiency oxidation and simultaneous cell integrity maintaining." Chemical Engineering Journal 461 (2023): 141880; Zhu, Tingting, and Bin Liu. "Mechanism study on the effect of peracetic acid (PAA), UV/PAA and ultrasonic/PAA oxidation on ultrafiltration performance during algae-laden water treatment." Water Research 220 (2022): 118705; Liu, Bin, et al. "Ultrafiltration pre-oxidation by boron-doped diamond anode for algae-laden water treatment: membrane fouling mitigation, interface characteristics and cake layer organic release." Water Research 187 (2020): 116435.).
- MCLR abbreviation is missing.
Response: Thanks for the review from the reviewer. The full name of MCLR was added when it first appeared in the manuscript.
- The modeling part is not explained in the appropriate way. What is the importance of modeling and fitting curves (Figure 5), how does it help this scope of the paper?
Response: Thanks for the review from the reviewer. We re-edited the order of the figures. In Fig. 5, the modeling and fitting curves implies the fouling model of the filtration process during different pretreatment duration. We can easily observe that the typical two stage model was varied to one stage model when oxidation duration over 60 min. This suggest that the cake layer formation was highly mitigated by the BDD anodizing when oxidation duration was 60 min and 100 min.
Round 2
Reviewer 2 Report
All comments have been addressed.
Reviewer 3 Report
The authors answered all the comments.
