Progress Towards Bioelectrochemical Remediation of Hexavalent Chromium

Round 1

Reviewer 1 Report

The review ‘Experiences towards bioelectrochemical remediation of hexavalent chromium’ gives a comprehensive description of the state of art. Despite the great number of publications, the topic has not been previously reviewed and thus such review is needed. The authors have screened the literature extensively and have included all of the relevant studies to the review. The review is well-constructed and the main factors affecting the reduction rates and removal efficiencies are well described in specific chapters. The authors also describe very well the possibilities and challenges of bioelectrochemical removal of hexavalent chromium from groundwaters.

 

The language of the manuscript, however, should be revised throughout, as some of the sentences are very confusing, e.g. lines 12-14, 20-25, 71-72, 86-88 and 136-139.

 

The authors should also re-consider some of the titles. I recommend leaving out the word ‘Experiences’ from the title of the manuscript or replacing it e.g. with ‘Aiming’, ‘Experimentation’ or ‘Progress’. The chapter 2 ‘Cr(VI) reduction in bioelectrochemical systems’ should also be re-titled as it is very similar to the title of chapter 3 and the chapter 2.1. discusses mainly about non-electrochemical bioprocesses.

 

To further improve the manuscript, the authors could clearly state the operational conditions, in which the highest reduction rates or most efficient removal have been achieved. The discussion regarding the most probable products of bioelectrochemical reduction of Cr(IV) from groundwaters in situ, their stability and possibility for Cr recovery could also be expanded, as well as the potential of bioelectrochemical systems in real-time monitoring.

Author Response

Reviewer comments:

The review ‘Experiences towards bioelectrochemical remediation of hexavalent chromium’ gives a comprehensive description of the state of art. Despite the great number of publications, the topic has not been previously reviewed and thus such review is needed. The authors have screened the literature extensively and have included all of the relevant studies to the review. The review is well-constructed and the main factors affecting the reduction rates and removal efficiencies are well described in specific chapters. The authors also describe very well the possibilities and challenges of bioelectrochemical removal of hexavalent chromium from groundwaters.

 

The language of the manuscript, however, should be revised throughout, as some of the sentences are very confusing, e.g. lines 12-14, 20-25, 71-72, 86-88 and 136-139.

Authors: Thank you for your kind review. We have checked the whole text trying improving its readability. The revised sentences (except for minor changes and formatting) are highlighted in the revised manuscript.

 

The authors should also re-consider some of the titles. I recommend leaving out the word ‘Experiences’ from the title of the manuscript or replacing it e.g. with ‘Aiming’, ‘Experimentation’ or ‘Progress’.

Authors: We agree and shanged the title in “Progress towards bioelectrochemical remediation of hexavalent chromium”. We would be happy about your opinion.

 

The chapter 2 ‘Cr(VI) reduction in bioelectrochemical systems’ should also be re-titled as it is very similar to the title of chapter 3 and the chapter 2.1. discusses mainly about non-electrochemical bioprocesses.

Authors: We re-titled the 2nd paragraph in “Principles of Cr(VI) Reduction in Bioelectrochemical Systems”. Our aim in this paragraph was to introduce the general processes that may lead to Cr(VI) reduction in a BES, i.e. 1) abiotic electrochemical reduction and 2) microbially mediated reduction. Accordingly we modified the structure of this section with a paragraph 2.1) on abiotic electrochemical processes and the 2.2) in which the microbial mechanisms of Cr(VI) reduction are discussed. These bioprocess do not occur only in BES, but there may took advantages.

 

To further improve the manuscript, the authors could clearly state the operational conditions, in which the highest reduction rates or most efficient removal have been achieved.

Authors: we have tried to indicate throughout the text the conditions that lead to the highest reduction rates, but our analysis has been limited due to the lack, in most of the revised studies, of relevant information (eg conductivity of the electrolyte, abundance and type of microorganisms at the cathode, ...) to allow a wide comparison between the different experiments.

 

The discussion regarding the most probable products of bioelectrochemical reduction of Cr(IV) from groundwaters in situ, their stability and possibility for Cr recovery could also be expanded, as well as the potential of bioelectrochemical systems in real-time monitoring.

Thank you very much for your very helpful and kind review – we appreciated your feedback and suggestions. These are all very interesting and unexplored topics. In the review we have provided references of the few studies on such aspects. We hope our ongoing tests will allow to collecting some interesting information and data to further discuss these aspects in the future.

Reviewer 2 Report

Overall this is a well organized review of the potential for bioelectrochemical remediation to help manage Cr(VI) contamination in water.  

The language is at sometimes very unclear - I did my best to note when I was not sure of the intent of your sentences.  There are extensive in text comments

This provided an extensive overview of the work that has been done and highlighted the research still needed to determine if bioelectrochemical remediation can be effectively used to mitigate Cr(VI). 

The table format was very difficult to read (though I understand why it was set up in the way it was).  It needs to be revised so the information is easier to read across the rows.

 

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Author Response

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