Microbial Selection for the Densification of Activated Sludge Treating Variable and High-Strength Industrial Wastewater

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The sedimentation performance of sludge is the key to the good treatment effect and stable operation of activated sludge process.  The results of this paper are of good value for understanding how to control and improve the sludge sedimentation performance when activated sludge treats industrial wastewater with high concentration and high fluctuation. The special paper's analysis of the reasons for the failure to achieve sludge granulation in the experimental process is very helpful to other researchers. 

Modification Suggestion:

1. Line 236: The detailed meaning of "SD" is unclear.

2. Line 296: What is the difference between DSVI and SVI? Detailed instructions should be given.

3. Line 436: "SVI10/SVI30 value

"≈1, 200 μm in size" is the expression incorrect?

4. The variation diagram of MLSS with the test running time should be given in the research results. The influence relationship between OLR and MLSS is clearly explained.

5. Lines 450-453: It is not convincing to regard the long age of sludge during the test as one of the reasons for the failure of granulation. In general, the core microorganisms of granular sludge should be slow-growing microorganisms, requiring a longer sludge age.

6. The results of the paper show that only by controlling stable OLR can the sludge sedimentation performance be stable. For the actual industrial wastewater treatment process with high fluctuation, the operation suggestion of activated sludge method should be put forward according to the test results.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This study investigates an activated sludge granulation with poor settleability.  The authors demonstrated that their concept using only microbial selection was not successful and needs to be improved. Despite the lack of success in this area, the presented research has cognitive value.

Significant revision is required in the interpretation of data and terminology. The detailed recommendations are as follows:

 Lines 34-35: Specify the country in which this region is located. Is the problem of sludge swelling unique to this region? Discuss this statement on a broader scale.

Line 41: Cl2 instead of Cl

Lines 76-80: Show the difference (comparison) between the use of dissolved oxygen by AGS compared to AS.

Line 104: Provide the full name of the AGMBR abbreviation.

Lines 125-134: Include a scheme of the research unit (SBR+MF >> MSBR).

Line 136: Specify the statement 'sludge properties were not good'.

Line 127: What was the mixing efficiency (rpm)?

Lines 135-139: Please clarify what exactly you mean by 'anaerobic feed was 300 min', 'anaerobic reaction was 180 min', 'aerobic reaction was 860 min'. What was the hydraulic retention time of the sewage in the reactor?

Line 148: Paragraph 2.2. (Small-scale MBR set up) refers to membrane unit.

Lines 171-180:  This part needs more detailed description to find the direct correlation with Section 3.4 (Membrane filtration experiments).

Lines 375-380: In what units are the data presented in Table 1a-c? Explain for a wider audience.

Lines 409-411: Discuss in more detail what components present in clarified wastewater will be responsible for the formation of the cake layer and the blocking of the pores.

Lines 393-394: On the basis of your research results, discuss the contribution of reversible and irreversible fouling of the initial permeability decline.

Fig. 7 Give an explanation (preferable in the Methods section) how FR was estimated.

The scale in Figure 7a is incorrectly selected.  The scale does not allow for the capture of changes in permeability.

The markers in Figures 7a and 7b differ, making the interpretation of the results difficult.

The authors should explain why they stopped at stating that granulation was unsuccessful and did not introduce any modifications during experimental procedures, especially in the context of available literature data.

Please comment on how varying oxygen concentration (1-4 mg O2/L) affects process stability, granulation, and microbial community. Why was not the oxygen concentration kept constant in the reactor?

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors addressed sufficiently all my questions.