Biological Desulfurization of Tannery Effluent Using Hybrid Linear Flow Channel Reactors

Round 1

Reviewer 1 Report

Dear Authors,

the topic of the recovery of elements in bioprocesses is an important direction of sustainable development. For this reason, I find your manuscript well however, it needs extensive work to be published. I hope you find my comments helpful, not discouraging.

1. line 25: You wrote „sulfide removal” and „sulfate reduction”. Please, be more accurate. Sulfide oxidation, sulfate reduction and sulphur removal.
2. lines 33: “SO = sulfate oxidation” => sulphide oxidation
3. I have the impression that in all text you use HS- and S2- interchangeably, e.g. in methodology you wrote about S2- measuring (lines 177, 186) and in results, you presented HS- concentration in reactors. I know it depends on pH, however, measurement methods of speciation forms differ from each other.
4. line 54: during gas exchange H2S could be removed, dissolved and dissociated HS- rather not, of course, HS- can be transformed to the H2S when pH is decreasing
5. line 61: the high concentration of organics – what order of magnitude of COD or TOC
6. Table 1: Cl=> Cl‾; H-TOC and L-TOC exist only in table caption, not in the table content; COD values are absent, but COD: sulphates and COD:TVS are present (please, complete COD values); in the table caption “mV” is present – why, when you didn’t present ORP values?
7. The raw and pre-treated TWW are significantly different. In experiments you used a mix of them (lines 113/115), so please give the characteristic of TWW after equalisation. Why equalisation was applied (please, add the information for the readers)?
8. Figure 1: a caption of the influent port is missing.
9. lines 128,129: How the active volume of 2L has been estimated? How was the domination of surface flow excluded? Please, explain in the methodology part.
10. Section 2.3. Maybe a timeline chart will be helpful to fast and easy catch the difference between HLFCR1 and HLFCR2.
11. Please explain carefully to the readers the main purposes of applying the HLFCR1 and HLFCR2 experiments.
12. How long did AD take? I do not see this information in section 2.4.
13. Section 2.6. Not all analytical methods are listed – in table 1 more parameters were presented. Maybe the source of table 1 is omitted and made measurements are properly described in section 2.6.
14. Figure 2: double INF symbol is present
15. Figures 2 and 3: Different colours of markers were used for measurement series of the same type. It is very hard to compare the series between fig.2 and 3.
16. Figure 2: EFF series is missing data (between 60 and 120 days). Ok, the reason is explained in lines 254/257, but why do the results of EFF appear on the days 120-140?
17. lines 216/218: What were ORP values of the influent (mixed TWW) and effluent from the reactor (reactors)? Can you add these data? It is very interesting.
18. lines 151,152: “It was then connected in series to HLFCR2” => “It was then connected in series to HLFCR1”
19. Fig. 3B – why sulphates increase in EFF in comparison to the concentration in SPF and SPB? The results of EFF are randomly and SPF and SPB results form a coherent series.
20. Generally, it will be more clear and easier for the reader when the results of sulphates and sulphides will be presented as S (mg/L) or just in mmol/L. The current form of the presented results is very confusing and requires the reader to be determined to follow the authors' thoughts. So, I think, a clearer balance sheet should be proposed. Please consider how to simplify the presented data.

Best regards

Author Response

Thank you for your feedback. Please see attached coverletter.

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors investigated Biological desulfurization of tannery effluent using hybrid linear flow channel reactors. I have follow specific comments.

 

1. Lines 112-115

Why did you use blended wastewater as substrate? How was the mixing ratio? In addition, please suggest the characteristics of blended wastewater used in this study.

2. Line 113

What is the "partially treated"?

 

3. Lines 141-142

It is difficult to understand operational methods of two HLFCRs. So, draw a figure describing operational methods.

 

4. Why did you operate two different reactor sets? The reason should be complemented in Introduction part.

 

5. Section 3.1

Why the sulfur reduction differed between HLFCR1 and HLFCR2? Please complement the reason with citing proper references.

 

6. Figure 2

Check typo errors. Something should be EFF.

 

7. Section 3.2

It is difficult to catch main point of the section 3.5. Please improve. In addition, suggest methane production data as figure.

 

8. Lines 427-434

Shorten or delete.

 

9. Conclusion

Current conclusion seems to be missed some important message. Please improve. In addition, please clearly suggest which method is more appropriate for post AD operation (The authors operated two different reactor sets.).

Author Response

Thank you for your feedback. Please see attached coverletter.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear Authors,

thank you very much for your improvement of the manuscript.

I still have some comments:

1. There are symbols (inverted triangles) in Figures 2 and 3 that are not explained.
2. I think, your explanation to my comment No. 19 should be added to the manuscript.
3.  My comment No. 18 wasn't applied in the text.

Best regards

Author Response

Please see the attachment.

Author Response File: Author Response.pdf