Effect of Carbon to Nitrogen Ratio on Water Quality and Community Structure Evolution in Suspended Growth Bioreactors through Biofloc Technology
and Xugang He 1,2,3,*Round 1
Reviewer 1 Report
The article does not present originality, however it deepens and contributes with new results for the area.
The introduction needs to be further developed, bringing more recent articles on the influence of the C / N ratio on the treatment of effluents with high nitrogen concentration, as well as on the bacterial community.
The material and methods part needs to be more detailed, with information such as diffuser size and porosity, air flow, how the C / N ratios were defined, which SMEWW method was used to determine the TSS, a more complete characterization of the effluent used, etc.
In the results we need a comparison with the literature, comparing and / or validating the results obtained.
The state of the art in the introduction is fundamental, so that we can evaluate the real contribution of this article.
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
This paper was well written! I do have a question on scaling up the size of the reactors?
Author Response
Response to Reviewer 2 Comments
Point 1: This paper was well written! I do have a question on scaling up the size of the reactors?
Response 1: Thank you very much for your recognition of our manuscript. The development of biofloc technology was derived from the contributions of previous researchers' work, and we are honored to continue researching the bioflocs. Our next work will focus on scaling up the size of the reactors. We will consider the feasibility of larger reactors from the following aspects:
1. In our study, the C/N reached 15, the bioflocs had obvious nitrogen-reducing properties, and the microbial community structure tended to be stable. Therefore, if the reactors are to be expanded, it is necessary to adjust the C/N ratio of the influent to maintain a relatively constant.
2. Explore the search for cheap carbon sources because glucose was expensive
3. Ensure adequate dissolved oxygen in the reactor. Adequate oxygen supply was necessary for heterotrophic microorganisms in the biofloc.
4. Because the volume of water in the reactor will increase when the culture is expanded, it is necessary to provide agitation because the agitation caused by aeration may not be sufficient to maintain the suspension state of the biofloc.
Reviewer 3 Report
・General Comments
The manuscript submitted by Gou et al. describes the effect of carbon to nitrogen ratio on water quality and community structure evolution. While the findings presented in this study should be of interest to the audience, it is my opinion that a rather substantial revision, based on the technical comments given below, is needed to make this manuscript suitable for publication.
・Specific Comments
1. Abstract
The abstract only contains the results of the experiments. The abstract should be rewritten as the general purpose of the proposed publication does not appear clearly.
2. Writing convention of the cited reference
The author names described before the reference number ([X]) should be deleted.
3. Line 87
The information about water sampling in the South Lake such as date, condition of the water quality or sampling point (surface layer, middle layer or bottom) should be added.
4. Line 121
The rationale of sedimentation time of 30 minutes should be described. The testing methodology used as a reference should be added.
5. Line 143
Space is required at the begging of the sentence.
6. Figure 1 (a)
The value of TAN concentration rises again from the 16 days from the begging of the experiment in the case of C/N 10. This behavior is not confirmed in other cases. Explanation of this result should be discussed.
7. 3.4.2. Evolution of bacterial community structure
The information about the life history of the representative or dominant bacterial species will help the readers to understand the relationship between the C/N ratio and bacterial community structure.
8. Figure 4 (b)
The figure legend is complicated. The bacterial species with low occurrence probability should be included to others.
9. Result of PCA
Figure 4 → Figure 5
10. Result of PCA: (a) and (b)
The explanation of each plot should be added.
11. Result of PCA, b
The plot is less-visible due to the circles indicating the classification result.
12. Figure 4 and 5
These two figures are overall confusing (small font of the explanation of the axis and low resolution of figures).
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 3 Report
The manuscript has been much improved and is in a nice condition now. I think this manuscript will be acceptable.
