Reduction of Cr(VI) by Synergistic Effects of Iron-Rich Biochar and Pseudomonas aeruginosa

Round 1

Reviewer 1 Report

The manuscript presents a systematic and thorough investigation on the reduction of Cr(VI) by iron-rich biochar and Pseudomonas aeruginosa. The  manuscript is very well-written and easy to follow. Details on the species of Cr, Fe and released phosphorus were thoroughly investigated and presented. 1. It will be good if the findings from this study could be compared with other studies using different biochar or bacteria in section 3.1
2. In addition, how is the Cr(VI) reduction performance using biochar/PA in this study compared with other studies? Please include a comparative table on reduction of Cr(VI) from other studies.

Author Response

Please see the attachment including the Response, the Revision with marked changes and the clean Version.

Author Response File: Author Response.pdf

Reviewer 2 Report

In the present article, the authors have evaluated the potential synergistic effects of Cr (VI) reduction by iron-rich biochar and Pseudomonas 10 aeruginosa (PA). A major revision is recommended:

i. Add more details in the introduction section for improving the novelty of the article.

ii. Details about physiochemical characterization are missing. Please introduce the methods used for characterization.

iii. Details about Statical methods not included.

iv. were the experiments not conducted in triplicate, as the error bar is missing/not visible clearly in some figures?

v. Instead of a pointwise conclusion, make it crisp

vi. You can improve the novelty by taking the help of the following articles:

a. Chromium adsorption on surface activated biochar made from tannery liming sludge: A waste-to-wealth approach. Doi: https://doi.org/10.1016/j.wse.2022.09.001

b. Sustainable reduction of Cr (VI) and its elemental mapping on chitosan-coated citrus limetta peels biomass in synthetic wastewater, Doi: 10.1080/01496395.2021.1993921.

c. A comprehensive review on emerging natural and tailored materials for chromium-contaminated water treatment and environmental remediation. Doi: https://doi.org/10.1016/j.jece.2022.107325

Author Response

Please see the attachment including the Response, the Revision with marked changes and the clean Version.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors studied the possibility of reducing Cr(VI) to Cr(III) in polluted water by simultaneous application of iron-induced biochar and pseudomonas aeruginosa. Major improvements need to be made before considering the manuscript for publication.

Some general comments:

-  The title is a little bit misleading. A better fit could be “Reduction of Cr(VI) by synergetic effects of iron-rich biochar and pseudomonas aeruginosa”.

-  The abstract should provide a brief overview of the research study. Therefore, a clear reference to the following questions should be made: What is the reason and relevance of proceeding this study? What investigations have been proceeded? What are the main relevant results and implications?

-  The conclusion should include an outlook and give further information on implications resulting from this study.

-  I encourage the authors to edit and improve the English of the manuscript and the supplementary information (preferably by a native English speaker). The quality and understanding of the article should be improved.

Some other specific comments:

-       How do the authors justify that different structures of the biochar (Fe-300 and Fe-800) were not relevant on the performance of iron in case of ZVI-based material?

-       The results show that the degradation rates with Cr + Fe-800 and Cr + PA are 0% and 35%, respectively. The combination of Cr + Fe-800 + PA has achieved a degradation rate of only 19%. What could be the reason for this reduced efficiency in the combination of Fe-800 and PA?

-       Results show that the total chrome could be reduced efficiently by the combination of Cr + Fe-300 + PA. Could the reduction efficiency be increased by prolonging the incubation time?

-       Could the precipitation of Cr and Fe affect the adsorption efficiency of the biochar?

-       Page 1 line 11: I would suggest using another word for “Interestingly”.

-       Page 1 line 37: There are already valid methods, as the authors state in the paragraph afterwards. However, more low-cost and specified methods should be investigated to reduce Cr(VI) to Cr(III) since conventional methods are either related to high expenses or the use of chemical precipitants.

-       Page 3 line 99: According to Figure 2, supporting information, the optimum is reached at approximately 18 h. The described optimal density of 0.8 – 1 does not correspond to the value in Figure 2, supporting information. Please clarify.

-       Page 3 line 118: An unobservable effect is described here. Although in Figure 3, supporting information, an effect can be observed, I think the relevance is not significant.

-       Page 3 line 128: It is written that Fe-300 + PA and Fe-800 + PA were not investigated in this study.  However, they are listed in the table below, Table 1.

-       Page 3 line 132: The title of the heading 2.4. could be misleading since it is more about the different processes not the mechanisms themselves.

-       Page 3 line 137: According to Figure S2, supporting information, the end of logarithm growth is not reached after 12 h. Can the authors explain the difference in their results and the results of the referenced methods in Zhang et al.?

-       Page 5 line 183: Changes of approx. 10 % can be observed in the total chrome concentration (Figure 1a). This should be described as such. Why is an increase of total chrome concentration to be observed? Please explain.

-       Page 5 line 191: The unit is missing for the first value. It is not clear what the starting values were, the authors are referring to.

-       Figure 2: Values described in Figure 2 are not constituent with units in Figure 1 and in the text. It would be easier for the reader to remain at the before mentioned unit.

-       Page 7 line 23: Why did the authors describe a 80% reduction efficiency when the fraction of Cr(VI) is reduced from 100% to approx. 75% and approx. 48% for Cr + Fe-300 + PA and Cr + Fe-300, respectively? Furthermore, the two values are referred to three figures (Figure 1a, b, c). Hence, the reference to Figure 1a is not comprehensible.

-       Page 7 line 245: How do the authors explain the strong change in the interaction effect of Cr + Fe-800 + PA at the 2^nd day from -4 to 7 and later again to around 0?

-       Page 8 line 265 and 277: What significance level was chosen for testing the significance of the result?

-       Figure 4b): Total phosphorous fraction in the figure is > 100%. The authors should explain this.

-       Page 11 line 387: The equation is not chemically balanced.

-       Table S1, supporting information: The labelling for STD is missing in the legend.

-       Figure S3, supporting information: What type of mineral medium was chosen for the investigation here: A or B?

-       Figure S5, supporting information: The y-axis title is misleading. Otherwise the marked initial Cr(VI) concentration would be 1 mg/L reduced Cr(VI).

-       Figure S7, supporting information: Values for Fe-300 are not clearly visible.

Author Response

Please see the attachment including the Response, the Revision with marked changes and the clean Version.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The article has been improved as per the comments. It can now be ACCEPTED FOR PUBLICATION.