High-Loaded Bioflocculation Membrane Reactor of Novel Structure for Organic Matter Recovery from Sewage: Effect of Dissolved Oxygen on Bioflocculation and Membrane Fouling

Round 1

Reviewer 1 Report

Recommendation: Accept only if required revisions are made

The submission details an interesting approach on high-loaded membrane bioreactors. Wastewater could be pre-concentrated using membrane technology to the range suitable for biogas production via anaerobic treatment. The study follows a similar work presented by Faust et al. work (Water research, 2014), who reported that higher DO was positively correlated to higher concentrations of EPS, and sludge flocs in the high DO reactor were reported to be bigger than in low DO reactor.  Daie et al. (Water 2018) investigated the COD removal efficiency and study the bioflocculation performance as well. They noted that higher biofolculation was obtained using high-rate contact stabilization-MBR compared to high-loaded-MBR. They observed that with increasing SRT, the bound EPS concentrations increased resulting in improved bioflocculation performance, which could thus mitigate membrane fouling the impact of bound EPSs on membrane fouling.

The authors undertake to describe DO's influence on bioflocculation and membrane fouling from the perspective of a microbial population, on the other hand they write that their goal is to illustrate the effect of DO on bioflocculation in an HLB-MR of novel structure (?) and the mechanism behind such effect. One objective has been achieved, the other has not.

I recommend to revise the manuscript at this stage as the authors would benefit from a more in-depth analysis of their results, a more clear presentation and a more focused paper.

The paper gives a detailed methodology and on the other hand, it is laconic in some fragments. Many interesting tests have been made, but there is no direct link between them, e.g. why were the metal ions (magnesium, calcium, and aluminum) measurements made? why haven’t the Authors investigated Fe2+/Fe3+.

I recommend shortening the introduction (it can start at line 38). In the manuscript, there are, however, several aspects that are very unclear for example:

L 68-69 .. as a stronger sewage treatment capacity, which boasts a promising application prospect, what do the Authors mean by “stronger sewage treatment capacity”

L 72 “real urban sewage in northern China” it could be just real urban sewage, details of the location can be given further in line 104

In the section of Experimental setup and operation parameters. There is no explanation why one reactor was aerated by oxygen and another by a mixture of nitrogen-air. Are there any interferences of nitrite on COD measurement?

The title of the article suggests that the Authors deal with sewage not water, and in the article there are interchangeable terms for water as the medium studied: L 103-107 In this study, raw water was extracted from… After collection, the sewage was… experimental water…

Abbreviations commonly known in technology should have their explanation for example PTFE

L.163-164 concentration factors of the concentrate CODTO relative to the influent CODTO

Concentration factors (CF) of wastewater and pollutants needs more information.

This indicated that the HDO reactor concentrated with a better effect (?) than the LDO reactor.

I also suggest the Authors do not repeat the same information throughout the manuscript DO concentration was 1-2 mg/L and DO concentration was 6-8 mg/L. If the authors use abbreviations (HDO, COD, LDO) in this case, they can also be used.

Overall, the work has a promising potential, and would certainly make a worthwhile contribution to the field of optimization of configuration of a MBR.

Author Response

Thanks for your comments and suggestions. We have already made replies and amendments in the original draft. Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

This manuscript studies the effect of dissolved oxygen on the flocculation in high loaded bioflocculation membrane reactor for concentrating organic matter in municipal wastewater. I have the following comments for the improvement of this manuscript:
1) If there is any methodological advancement or novelty, it should be included in the title. Otherwise, the title does not suggest any novelty or interest.

2) What is the scientific contribution (methodological and practical) of this paper at the academic level?. No message about the scientific relevance of the study to the general readership in abstract and introduction.

3) Novelty: There is no enough novelty. Please explain the research significance.

4) What is the hypothesis?

5) New references (2019 and 2020) are required.

6) Why and how did you choose the DO concentrations of 1-2 mg/L and 6-8 mg/L?

7) Authors claim that the species in the precipitate like Trichococcus, Ornithinibacter, and norank_f__Saprospiraceae may have a positive effect on bioflocculation. How and why?

Author Response

Thanks for your comments and suggestions. We have already made replies and amendments in the original draft. Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Manuscript Number: sustainability-909930

Title: Effect of Dissolved Oxygen on the Flocculation in High Loaded Bioflocculation Membrane Reactor for Concentrating Organic Matter in Municipal Wastewater

Article Type: article

 

In the manuscript the experimental research concerning flocculation performance of high-loaded bioflocculation membrane reactor is presented. In experiments two different dissolved oxygen concentration were used as well as the raw water from grit chamber of a Jilin Province municipal sewage treatment plant. The manuscript is very well written. The materials, experimental procedures are described properly. An interesting discussion of results is delivered. According to the WebOfScience database authors have vast experience in the wastewater treatment. Below I am presenting my remarks:

1. What was the volume of the sample taken from the treatment plant? How many samples were taken? Were they taken at the same time or in a given period of time (e.g. 3 days)? Could authors comment if the initial physicochemical and biological properties of the sample could influence the results of their research?
2. Figure 4: Authors should specify the fraction term. Is it the fraction of particles number? Usually such quantity is used in the Population Balance modelling whereas in the practical (engineering) application volume fractions are used. They allow for better assessment of physicochemical properties of the suspension and thus for better design subsequent unit operations, e.g. drying. Moreover the raw water was filtrated using 3 mm sieves. However the particle size distribution ends on 100 um. Why?
3. Figure 5: the color scheme has to be changed. The deviation bars are not visible.

Author Response

Thanks for your comments and suggestions. We have already made replies and amendments in the original draft. Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

There is no enough novelty and the hypothesis was not well explained.

Please revise the following sentence in the abstract:

"In this study, high loaded bioflocculation membrane reactor (HLB-MR) of novel structure for organic matter recovery from sewage, with the research purpose of the effect of dissolved oxygen (DO) on bioflocculation and membrane fouling."

Author Response

Please see the attachment.

Author Response File: Author Response.pdf