Influence of Inoculum Thermal Pretreatment Time on Hydrogen Production in Dark Fermentation^†

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Manuscript authored by Domińska et al., attempted to study the impact of thermal pretreatment on hydrogen production from kitchen waste. However, this seems a routine work that was carried earlier in literature and novelty is not defined. Several supporting analysis and important indicators for biohydrogen production are missing. Feasibility of large-scale implementation and thermal pretreatment effects were not discussed. This manuscript needs significant revision.

Novelty is missing in the work. There have been several studies already carried out on biohydrogen from this substrate. Please provide justification and define clearly about how this work differs from the previous literature

The following lines need to be justified clearly mentioning the scientific uniqueness of the current work.

‘The aim of the study was to investigate the effect of inoculum thermal pretreatment time on H₂ and VFAs production in the DF process. The effect of adding inoculum to KW on the biohydrogen production yield was also tested’.

What was the reason for choosing the operational pH in above neutral range of 7.3 to 7.6? References could be cited.

What is the rate of substrate degradation? COD results are not provided.

What are the initial values of VFA present in the substrate?

Does the heat pretreatment has effect lasting for long term?

Comments on the Quality of English Language

Moderate editing of English language required.

Author Response

Dear Sir or Madam, 

thank you very much for the valuable remarks concerning our manuscript.  

1. Novelty is missing in the work. There have been several studies already carried out on biohydrogen from this substrate. Please provide justification and define clearly about how this work differs from the previous literature 

Authors Response:

A rationale is provided and how this work differs from previous literature is identified (page 3, line 92-124). 

2. The following lines need to be justified clearly mentioning the scientific uniqueness of the current work. 

What was the reason for choosing the operational pH in above neutral range of 7.3 to 7.6? References could be cited. 

Authors Response:

The pH was not selected or regulated, it results from the pH of sewage sludge used as inoculum, as well as the pH of kitchen waste. 

What is the rate of substrate degradation? COD results are not provided. 

Authors Response:

COD was not measured in the study due to the fact that the substrate is complex, which negatively affects the correctness of the results of this study. Instead of COD TOC was measured. 

What are the initial values of VFA present in the substrate? 

Authors Response:

At the beginning, the total content of VFAs was measured, and the results were below 500 mg CH3COOH/dm3  

Does the heat pretreatment has effect lasting for long term? 

Authors Response:

Thermal treatment of the inoculum is performed before each subsequent DF process. The long-term effect of pre-heating the inoculum has not been tested. At the moment, research is being carried out on a periodic basis, on a laboratory scale. On a large scale, thermal treatment is sought due to the energy consumption of heating. 

Yours faithfully 

Reviewer 2 Report

Comments and Suggestions for Authors

General remarks

The manuscript deals with a very hot and interesting topic, besides perfectly fits to the scope of Energies. Results and conclusions are remarkable, based on a relevant methodology, therefore they can contribute to the development of biological hydrogen production, However, literature should be extended, a few formal inaccuracies also needs minor corrections. I consider the manuscript very promising and hope that my comments may help for the authors to make the manuscript better and suitable for fast publication.

Detailed comments

 1.     Some of the keywords (hydrogen, dark fermentation) should not be the same as the words in the title. Differential expressions may result more shots via search engines and make the future citations easier.

2.     References are up-to-date and relevant, however I am of the opinion that should be extended in order to well-supporting the remarkable own results. My recommendations: (1) The sources in the Discussions (No. 20-26) could be detailed and introduced also in the literature section. Besides they should remain also in the Discussions (shortly), as a basis of the comparision.

(2) The competitive processes for hydrogen production might be detailed a little more (e.g. in a table).

(3) A comparision of the goods and bads of maximization of hydrogen and methane production might also highlight the importance of the research topic.

3.     Table 1 and 2: „C” in the last columns means carbon, or methane? Abbreviations (TS, VS) firstly should be written in whole form, or introduce in a special table for abbreviations in the end of the manuscript.

4.     The quality of the produced hydrogen might be also introduced, since you mentioned that it is typically impure.

5.     Conclusions are basicly well-written, however I miss the future directions and (as it is  anovel area) the limitations of the research in this field.

In a nutshell, the topic is very interesting, and has great potential for the readers, but the elaboration of the manuscript (especially the literature section) should be improved based on the recommendations so that it may reach the level of publishing in the Energies. Congratulations for the authors and good work!

Author Response

Dear Sir or Madam, 

thank you very much for the valuable remarks concerning our manuscript. According to your advices the article was corrected. 

1. Some of the keywords (hydrogen, dark fermentation) should not be the same as the words in the title. Differential expressions may result more shots via search engines and make the future citations easier.

Authors Response: 

Keywords have been changed. 

2. References are up-to-date and relevant, however I am of the opinion that should be extended in order to well-supporting the remarkable own results.

Authors Response: 

Sources from the Discussions are also presented in the literature section and other sources have been added. Competitive hydrogen production processes are described in the table. 

3. Table 1 and 2: „C” in the last columns means carbon, or methane? Abbreviations (TS, VS) firstly should be written in whole form, or introduce in a special table for abbreviations in the end of the manuscript.

Authors Response: 

The markings C, TS, VS in the tables have been corrected.  

4. The quality of the produced hydrogen might be also introduced, since you mentioned that it is typically impure.

Authors Response: 

The composition of the gas produced in DF was described. 

5. Conclusions are basicly well-written, however I miss the future directions and (as it is  anovel area) the limitations of the research in this field.

Authors Response: 

Planned future research directions as well as problems that may be encountered have been added in the conclusions. 

Yours faithfully 

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript entitled “Influence of inoculum thermal pretreatment time on hydrogen production in dark fermentation” by Marlena Domińska and her colleagues was completely revised with interest. The manuscript deals with investigation of the effect of inoculum thermal pretreatment time on hydrogen and volatile fatty acids production using dark fermentation process. The manuscript has some novelty and the work seems to be completed with good English witting. I recommend accepted for publication after minor revision.

Comments

1-        The keyword should be rewritten

2-        L 26-30 should support by references

3-        The authors should support the conclusion at the end of the introduction as well as the novelty of the proposed work for future possibilities.

4-        Section 2.3. should support by more information about the condition used and the supplier of the equipment

5-        Conclusion should be revised

Author Response

Dear Sir or Madam, 

thank you very much for the valuable remarks concerning our manuscript. According to your advices the article was corrected. 

1. The keyword should be rewritten.

Authors Response: 

Keywords have been changed. 

2. L 26-30 should support by references.

Authors Response: 

References added to this statement. 

3. The authors should support the conclusion at the end of the introduction as well as the novelty of the proposed work for future possibilities.

Authors Response: 

The conclusion at the end of the introduction has been corrected, and new information and opportunities for future work have been added.  

4. Section 2.3. should support by more information about the condition used and the supplier of the equipment.

Authors Response: 

Section 2.3 has been extended. 

5. Conclusion should be revised.

Authors Response: 

Planned future research directions as well as problems that may be encountered have been added in the conclusions. 

Yours faithfully

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Section 3.4 could be elaborated and discussed in relevance to VFA and gas production. As the mansucript is linked and based on carbon utilization for gas production, this section deserves a detailed discussion.

Comments on the Quality of English Language

Can be improved 

Author Response

Dear Sir or Madam,

thank you very much for the valuable remarks concerning our manuscript.

Section 3.4 could be elaborated and discussed in relevance to VFA and gas production. As the mansucript is linked and based on carbon utilization for gas production, this section deserves a detailed discussion.

Authors Response:

In section 3.4 has been added elaborated in relevance to VFAs and gas production.

Yours faithfully