Saline Sediments as a Suitable Source for Halophilic Inoculums to Degrade Azo Dyes in Synthetic and Real Textile Wastewaters by Microbial Electrochemical Systems

Round 1

Reviewer 1 Report

The objective of this study was to design microbial bioanodes capable of treating (i) synthetic textile wastewater (STWW) and (ii) real textile wastewater (RTWW) containing the two azo dyes TB and/or BR using an electromicrobial process involving electroactive halophilic bacteria already adapted in hypersaline sediments of extreme Tunisian environments.

In general, the paper is well written and understandable, then it contains less grammatical errors.
Specifically, the FTIR data analysis part is not supported by scientific sources.
The legend of figure 6 is not explicit, and figures 6f and 6g are not commented? why?
Also, the legend of figure 7 is difficult to understand, for example, I do not see the small "a" on the figures. Moreover, when you enlarge an image from X 5000 to X 10 000, the sizes should change too, but why does it stay the same 1µm (i.e. medium and high conditions) ?

Author Response

The objective of this study was to design microbial bioanodes capable of treating (i) synthetic textile wastewater (STWW) and (ii) real textile wastewater (RTWW) containing the two azo dyes TB and/or BR using an electromicrobial process involving electroactive halophilic bacteria already adapted in hypersaline sediments of extreme Tunisian environments.

Comment 1: In general, the paper is well written and understandable, then it contains less grammatical errors.

Specifically, the FTIR data analysis part is not supported by scientific sources.

The references used to discuss the FTIR part are now added in the section 3.3. “Monitoring of decolorization of TB and BR in RTWW: COD and FTIR analyses.”

Comment 2: The legend of figure 6 is not explicit, and figures 6f and 6g are not commented? why?

The legend of figure 6 is added.

Figures 6f and 6g correspond to the STWW-TB-SSM and RTWW-SSM treated groups. Compared to the FTIR spectrum of the control sample, the absorption peak of the azo vibrations was significantly reduced (as in 6c, d and e). The codes have been added in the text and the reference articles used to discuss the FTIR part are well added too.

Comment 3: Also, the legend of figure 7 is difficult to understand, for example, I do not see the small "a" on the figures. Moreover, when you enlarge an image from X 5000 to X 10 000, the sizes should change too, but why does it stay the same 1µm (i.e. medium and high conditions) ?

The legend of figure 7 is now improved and the abbreviations a, b and c are deleted. The different magnifications are now readable directly on the figure.

Between the x5000 and x10000 magnification, the length of the 1µm scale is different. The length of the white bar is bigger for the x10000.

The sizes of the different micrographs are enlarged to better visualize the scale.

Author Response File: Author Response.docx

Reviewer 2 Report

I read the paper and I can support it for acceptance after the revision of considering my comments below: 

1) In my eyes, the discussion is weak. Comparison with others in the literature could reflect the advantage of the current study. 

2) Most of the figures are poor in quality and should be improved.

3) Updated reference papers/literature should be cited especially some studies in 2023

4) Make sure to use the abbreviation when the full term is firstly appeared in the text.  There are many places in the text for such kind of improper use, please chekc and correct them all.

The paper will be benefitted after the proofreading of language checking. 

Author Response

I read the paper and I can support it for acceptance after the revision of considering my comments below:

Comment 1: In my eyes, the discussion is weak. Comparison with others in the literature could reflect the advantage of the current study.

èFollowing your comment regarding the discussion, we have added the following discussion items which you will find highlighted in the new version of the manuscript.

- A discussion about the tolerance of salinity in a synthetic textile effluent containing an azo dye group and deduce the advantage of using an extreme halophilic microflora versus a moderately extreme microflora, based on the latest publication that has to be used halophilic microorganisms for treating saline effluents.

- A discussion based on the comparison with a publication on the effect of initial dye concentration on fade rates. we deduce that the common point that we share with this study is that at low concentrations which do not exceed 600mg/L, the decolorization rates have always exceeded 70%.

- A discussion with another study recently published on the influence of the combination of the two electrochemical and biological approaches in the same unit. we explained the difference in the reduction pathways of azo molecules between a conventional biological reactor and a bioelectrochemical reactor, and how the specific extracellular reduction pathway of the electroactive community protects bacteria by keeping the dyes and their intermediates out of the cell. which significantly reduces bacterial toxicity.

Comment 2: Most of the figures are poor in quality and should be improved.

èFigures 1, 2, 3, 4, 5 and 6 were modified (size, font, scale) and then run through an online image optimizer to improve resolution.

Comment 3: Updated reference papers/literature should be cited especially some studies in 2023.

èThis table summarizes the different references added

Comment 4:  Make sure to use the abbreviation when the full term is firstly appeared in the text.  There are many places in the text for such kind of improper use, please chekc and correct them all.

Abbreviations that appear for the first time in the text are checked and corrected:

• Abbreviation 1: TWW (Line 11).
• abbreviation 2: COD (Line 20).
• Abbreviation 3: CA and CA (Line 95).
• Abbreviation 4: SEM (line 97).

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Can I suggest to remove Eq. (1) and (2) as they are too simple and will negatively affact the paper in some readers eyes.

Author Response

Comment: Can I suggest to remove Eq. (1) and (2) as they are too simple and will negatively affact the paper in some readers eyes:

Equations (1) and (2) have been deleted in the new version of the manuscript in the section 2.3. Monitoring of decolorization, quantification of COD, and measurement of azo dye biodegradation.