The Use of Natural Minerals in a Pilot-Scale MBR for Membrane Fouling Mitigation

Round 1

Reviewer 1 Report

This study aims at identifying fouling mitigation effects on the membrane by adding inert material (bentonite and Zeolite) in a membrane bioreactor with charged (10x) synthetic wastewater as feed. The manuscript contents are written very clearly especially the introduction and methodology section. From the reviewer’s perspective, these sections give a clear outlook on the state of the art, the problem statement and describe the methods applied. However, some parts of the method and the whole result section is poorly developed and would require some more attention from the authors.

• A total of 20 concentrations of bentonite and additional 20 concentrations of zeolite were tested to find an optimum concentration. So overall of 40 concentrations. However, looking at the last figure (L293) it seems the total tests were conducted in 16 days. This seems really bizarre; the authors did not mention how long each test was conducted and how the fouling was made to develop. Fouling analysis is done only after the membrane gets clogged and I believe the authors did not explain how long each concentration was assessed and if underdeveloped fouling was analyzed then the true potential of the bentonite or zeolite was never be realized.
• Normally membrane fouling is described by filtration resistance. That is intrinsic membrane resistance, removable fouling resistance, reversible organic fouling resistance, reversible inorganic fouling resistance, irreversible fouling resistance which is all equal to total filtration resistance. It is surprising to see the authors have categorized only 2 kinds of fouling in their paper i.e. reversible and irreversible fouling. This makes the analysis weak i.e. under their analysis removable fouling, reversible organic fouling and reversible inorganic fouling is clubbed into reversible fouling and irreversible fouling. As the authors are adding inorganic inert material and not measuring its fouling impact separately, it makes it quite difficult to judge the effectiveness of the study.
• Also, it would be wise to make a % fouling analysis pie chart to see how the fouling type changes for various concentrations better understand where the fouling is contributing towards. Normally if irreversible fouling is more than 1 % then the intervention might not be a good one.
• Did the authors use a new membrane for each experiment? If no, then how reliable is the data?
• Did the authors calculate the membrane resistance first and fouling resistance later on? What is the proportion of removal, reversible and irreversible fouling on the membrane surface after each experiment?  
• The authors have to present the data together as a % contribution of total fouling resistance.
• Fig 2, 3, 4,5: It’s not necessary to put a 3D graph here. Can the authors change the data to a 2D graph so that the axis can be ready correctly? Also, why the data is split between the two ranges. It would be better to see the low and high bentonite (zeolite too) concentration on a single long horizontal graph.
• There is a lot of data from Figures 2 to 5 and the authors have not taken time to elaborate on these results.
• Data doesn’t seem to highlight that these many tests reveal anything substantial as most +ive effects are seen at 3 g/L
• It seems like adding/not removing bentonite / Zeolite does not make a huge difference as the data reversible fouling in MBR's are normally between 20 -30 %, recoverable 70-80 % and irreversible ideally be less than 1 %. But as seen here adding bentonite in the best-case scenario does not outperform normal MBR operation. If the reviewer has misunderstood the author's interpretation. Do clarify in the corrections.
• Fig 1 should be Figure 8: Typo. Additionally, the data shows that the authors only measure the effluent only 4 times in 16 days.

Just a comment the authors need not comment or address this in their manuscript. Feed quality though elevated however ideal feed for digestion C: N:P ratio so it’s not remarkable to see a good effluent quality. Most MBR has problems when the nitrogen and phosphorus are in imbalance. So, when the authors are developing the newer continuous inert addition experiment, they can imagine a nutrient imbalance to see how the fouling develops.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Text is written in correct english, no significant mistakes were detected during review. 

Small mistake in chapter title was found 3.1. Effect of bentonite and zeolite on membrane foulin - please check foulin to fouling

Line 278, 279 - Total Suspended Solids, Total Nitrogen - I think capital letters are not needed

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have revised the manuscript according to my suggestion. Authors should proof read the manuscript for errors and from myside the manuscript is good to go.