Management of Tanning Waste from Leather Processing by Anaerobic Digestion Using a Dynamic Method on a Semi-Technical Scale

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Title: Management of tanning waste from leather processing by anaerobic digestion using a dynamic method on a semi-technical scale.

The research presented here was intended to demonstrate the decomposition of the flesh in the process, to confirm its biogas yield, and to evaluate the biological and technical parameters of the process. The manuscript still needs further revisions and improvements. The modification suggestions are as follows:

Q1. Page 2, line 4: Please harmonize and use the correct format for units throughout the text.; e.g. 𝑔 𝐶𝑂2𝑒𝑞/𝑘𝑊ℎ Mg, ODM*Mg-1*d-1 and so on. The symbol ‘*’ is generally modified uniformly to ‘·’.

Q2 Page 3, lines 1-7: Please format the fonts consistently and correctly. In addition, please revise the formatting of the fonts in the tables according to the requirements of the journal.；A description of progress in biogas research is missing from the Introduction, please refer to Chemical Engineering Journal 468 (2023) 143490.

Q3 Page 2, line 1. This sentence makes no sense, so please delete it.

Q4 Page 2, line 4: Beneficial factors? Please indicate which factors.

Q5 Page 2, lines 8-12: This sentence needs to be simplified and rewritten.

Q6 Page 2, lines 20-22: How did you arrive at this conclusion?

Q7 Page 3, lines 1-10: These two paragraphs stand-alone very abruptly.

Q8 The author's content in the introductory section needs to be further refined and revised and lead to the focus of the research in this paper.

Q9 2.2. Substrate processing levels: lines 8-10: How did you come to this conclusion?

Q10 2.3. Leather wastes (white and blue): data should be summarised and presented in tabular form.

Q11 2.5. Mixture of leather shaping and animation: lines 3-5: From the author's explanation, I cannot obtain effective information.

Q12 Page 6, lines 2-3: However, even in situations where biogas production is low, it is still necessary to analyze the composition of biogas to ensure its safety and suitability.

Q13 Table 2: The abbreviations "C" and "O" need to be defined

Q14: This sentence needs further elaboration: Despite the variability of this ratio, the marked increase in volatile fatty acids is indicative of the faster saturation of the methanogenic bacteria and therefore also of the lower maximum organic load that can be applied to the fermentation of blue leather shavings compared to white leather shavings.

Q15 Is there any other reason or possibility? I need to explain the reason again. Contrary to initial assumptions and attempts to ferment blue leather shavings using a static method, it was shown that blue leather shavings have many times the biogas yield of white leather shavings.

Q16 Fig.6: Please explain the reason why the stability of biogas production in Experiment 3 is superior to other experiments. Is this related to the presence of glycerol? Adding more glycerol on a given day than in the process steps where these peaks do not exist?

Q17 "Higher hydrogen production would allow even higher methane values to be achieved", please provide evidence.

Q18 This article can provide more professional suggestions for future research development.

 

 

Author Response

Q1. Page 2, line 4: Please harmonize and use the correct format for units throughout the text.; e.g. ? ??2??/??ℎ Mg, ODM*Mg-1*d-1 and so on. The symbol ‘*’ is generally modified uniformly to ‘·’.

Response1: Thank you for pointing this out. We agree with this comment. This has been corrected.

Q2 Page 3, lines 1-7: Please format the fonts consistently and correctly. In addition, please revise the formatting of the fonts in the tables according to the requirements of the journal.；A description of progress in biogas research is missing from the Introduction, please refer to Chemical Engineering Journal 468 (2023) 143490.

Response2: Thank you very much for your valuable comment. The subject of biogas is a very broad topic due to the possibilities of the process, technologies used, materials or technical solutions. The article is known to the authors and will certainly be cited in future articles. The research included various forms of biochemical conversion of flesh. The research described in the article focused on semi-technical scale analysis, evaluation of the technology's scalability in terms of multiple parameters, regulation of specific process parameters so as to minimize the environmental impact of the solution, and obtaining a method of disposing of the problematic organic waste.

Q3 Page 2, line 1. This sentence makes no sense, so please delete it.

Response3: Thank you for pointing this out. We agree with this comment. This has been corrected.

Q4 Page 2, line 4: Beneficial factors? Please indicate which factors.

Response4: Thank you for pointing this out. We agree with this comment. This has been corrected.

Q5 Page 2, lines 8-12: This sentence needs to be simplified and rewritten.

Response5: Thank you for pointing this out. We agree with this comment. This has been corrected.

Q6 Page 2, lines 20-22: How did you arrive at this conclusion?

Response6: Unfortunately, I don't know which formulation we are talking about. Any statement that is not within the scope of basic chemical-physical knowledge, I tried through the literature.  I would ask you to indicate exactly which statement you are referring to.

Q7 Page 3, lines 1-10: These two paragraphs stand-alone very abruptly.

Response7: Thank you for pointing this out. We agree with this comment. This has been corrected.

Q8 The author's content in the introductory section needs to be further refined and revised and lead to the focus of the research in this paper.

Response8: Thank you for your valuable comment. The team in this research focused on the processing of tannery shavings in the context of solving the problem of their disposal for the company in the economic sense. Hence the decision to prepare a literature review highlighting the role of biogas plants not only agriculture, but also energy and environmental engineering. In the opinion of the authors, the role of these facilities is still under-promoted in the context of the positive impact of these installations on the environment. The authors try to prove that the operation of biogas plants on substrates that are not commonly used is possible. We ask you to understand the presented literature review in relation to the presented research and analysis results.

Q9 2.2. Substrate processing levels: lines 8-10: How did you come to this conclusion?

Response9: Thank you for pointing this out. We agree with this comment. This has been corrected.

Q10 2.3. Leather wastes (white and blue): data should be summarised and presented in tabular form.

Response10: Thank you for pointing this out. The organoleptic evaluation and basic description of the material's characteristics are intended to help visualize this substrate. Some of them have a numerical value, while others are descriptive. The results of this evaluation do not affect the subsequent results of anaerobic digestion, nor are they necessary for the analysis that follows. Therefore, the team found it unnecessary to present the evaluation results in a table, of which there are quite a few in the article anyway.

Q11 2.5. Mixture of leather shaping and animation: lines 3-5: From the author's explanation, I cannot obtain effective information.

Response11: Thank you for pointing this out. The authors in this piece point out the process aspect, which is not measurable but has a key impact on biogas technologies, especially on a large scale. We have included in this paragraph detailed information regarding the change in dosing methodology at the biotechnology start-up stage. Regarding your comments, we have included a broader explanation of this paragraph.

Q12 Page 6, lines 2-3: However, even in situations where biogas production is low, it is still necessary to analyze the composition of biogas to ensure its safety and suitability.

Response12: Thank you for pointing this out. Unfortunately, the team only had a biogas analyzer at its disposal, whose minimum measurement volume is 250 ml. With too small a volume of biogas produced, the readings are far from real.

Q13 Table 2: The abbreviations "C" and "O" need to be defined

Response13: Thank you for pointing this out. We agree with this comment. This has been corrected.

Q14: This sentence needs further elaboration: Despite the variability of this ratio, the marked increase in volatile fatty acids is indicative of the faster saturation of the methanogenic bacteria and therefore also of the lower maximum organic load that can be applied to the fermentation of blue leather shavings compared to white leather shavings.

Response14: Thank you for pointing this out. We agree with this comment. This has been corrected.

Q15 Is there any other reason or possibility? I need to explain the reason again. Contrary to initial assumptions and attempts to ferment blue leather shavings using a static method, it was shown that blue leather shavings have many times the biogas yield of white leather shavings.

Response15: Yes, the possible reasons for this are described in the article.

Q16 Fig.6: Please explain the reason why the stability of biogas production in Experiment 3 is superior to other experiments. Is this related to the presence of glycerol? Adding more glycerol on a given day than in the process steps where these peaks do not exist?

Response16: The DTR F120 fermenter has a substrate buffer tank from which the substrate mixture of the anaerobic digestion process is drawn. This tank has a capacity of about 15 liters, so that it is possible to fill it up and over the next few days there is an automatic dosage of the set dose. Although the material was well mixed, some fractions with higher density could get to the bottom of the buffer tank and be administered at a slightly different concentration than the daily test dose.

Q17 "Higher hydrogen production would allow even higher methane values to be achieved", please provide evidence.

Response17: The team felt that we did not need further analysis of hydrogen production in the hydrolysis process or its dosage to the reactor, so this statement was removed.

Q18 This article can provide more professional suggestions for future research development.

Response18: Thank you for pointing this out. We agree with this comment. This has been corrected.

Reviewer 2 Report

Comments and Suggestions for Authors

 

This study aimed to evaluate the biogas yield of leather shavings using the dynamic anaerobic digestion process plant, and to evaluate the biological and technical parameters of the process. It is an interesting research work and will be useful for the readers of the journal. However, the manuscript also needs revisions. The detailed comments are as follows:

1. Please mark the full name of the first abbreviated word in the text, for example, paragraph 1,GHG, P2, LCA, etc.

2. There is too much in the introduction, please reduce it.

3. Please add an introduction about leather shavings as well as its research with anaerobic digestion and biogas.

Materials and methods:

4. Please add the characteristics of the leather shavings, sludge, such as, total carbon,total nitrogen, total solids, etc.

 Results and discussion:

5. Table 6, Comparing different experiments, ANOVA should be done to analyze the differences more clearly.

6. Table 6, The full names of DM, FOS and TAC should be marked in the table notes.

7. The second direct reason for this is the low biogas production, and this is related to the long biogas conditioning time in the digester. This favours the synthesis of hydrogen and carbon dioxide to methane thereby lowering the proportion of CO2 in the biogas. Higher hydrogen production would allow even higher methane values to be achieve, Add references.

8. Table 8 and Table 9,  ANOVA should be done to analyze the differences more clearly.

9. Conclusion: There is too much content in the conclusion. Please rewrite the conclusion and summarize the whole article in concise and clear language.

10. References, Please standardize the reference format according to the requirements of the journal.

 

Author Response

This study aimed to evaluate the biogas yield of leather shavings using the dynamic anaerobic digestion process plant, and to evaluate the biological and technical parameters of the process. It is an interesting research work and will be useful for the readers of the journal. However, the manuscript also needs revisions. The detailed comments are as follows:

1. Please mark the full name of the first abbreviated word in the text, for example, paragraph 1,GHG, P2, LCA, etc.

Response1: Thank you for pointing this out. We agree with this comment. This has been corrected.

2. There is too much in the introduction, please reduce it.

Response2: Thank you for pointing this out. We agree with this comment. This has been corrected.

3. Please add an introduction about leather shavings as well as its research with anaerobic digestion and biogas.

Response3: Thank you for pointing this out. We have prepared a literature review in terms of full-scale biogas technologies, for the reason that previous studies (done by the static method) dealt with the substrate under study. The purpose of this study was to address the scaling of biogas technologies and their cooperation with other energy sources, especially in terms of on-farm demand. A detailed overview of the production and characteristics of the processed material is presented in the study by Wrzesinska-Jędrusiak et al. [44]. All relevant information for the presented research and analysis is presented in Section 2. Materials and methods.

Materials and methods:

4. Please add the characteristics of the leather shavings, sludge, such as, total carbon,total nitrogen, total solids, etc.

Response4: The basic results of the leather shavings analysis are included in Table 1. Other characteristics are presented in Sections 2.3 and 2.5. 

Results and discussion:

5. Table 6,Comparing different experiments, ANOVA should be done to analyze the differences more clearly.

Response5: Thank you for pointing this out. We agree with this comment. This has been corrected.

6. Table 6,The full names of DM, FOS and TAC should be marked in the table notes.

Response6: Thank you for pointing this out. We agree with this comment. This has been corrected.

7. The second direct reason for this is the low biogas production, and this is related to the long biogas conditioning time in the digester. This favours the synthesis of hydrogen and carbon dioxide to methane thereby lowering the proportion of CO2 in the biogas. Higher hydrogen production would allow even higher methane values to be achieve, Add references.

Response7: The team felt that we did not need further analysis of hydrogen production in the hydrolysis process or its dosage to the reactor, so this statement was removed.

8. Table 8 and Table 9, ANOVA should be done to analyze the differences more clearly.

Response8: Thank you for pointing this out. We agree with this comment. This has been corrected.

9. Conclusion: There is too much content in the conclusion. Please rewrite the conclusion and summarize the whole article in concise and clear language.

Response9: Thank you for pointing this out. We agree with this comment. This has been corrected.

10. References, Please standardize the reference format according to the requirements of the journal.

Response10: Thank you for pointing this out. We agree with this comment. This has been corrected.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

A description of progress in biogas research is missing from the Introduction, please refer to http://doi.org/10.1016/j.ijhydene.2023.07.086

Comments on the Quality of English Language

English moderation

Author Response

A description of progress in biogas research is missing from the Introduction, please refer to http://doi.org/10.1016/j.ijhydene.2023.07.086

Response1: Thank you for the proposal. After analyzing the article, I find that the research conducted in the article on pyrolysis processes has very little to do with the anaerobic fermentation research conducted in the article. Your proposed research is beyond the scope of the work shown in this article and lacks common elements. We will keep this article in mind if we prepare publications on similar termochemical issues.