Hydrolysis of Food Waste with Immobilized Biofilm as a Pretreatment Method for the Enhancement of Biogas Production

Round 1

Reviewer 1 Report (Previous Reviewer 3)

I believe that the authors took into account all my comments and the article can be published in Sustainability.

Author Response

Dear Reviewer,
On behalf of my team, I would like to thank you for your interest in our work to improve the manuscript.
cdlt

Reviewer 2 Report (New Reviewer)

Sustainability

 

Manuscript ID:           sustainability-2112921

Title:                            Hydrolysis of food waste with immobilized biofilm as a pretreatment method for the enhancement of biogas production

 

 

I think that is a very interesting experimental study. I recommend a publication of this work to Sustainability journal after the authors consider the following minor revision.

 

 

Comment #1

The authors need to improve their reference list as they have used only 45 references. I think that they should aim for at least 5 references in order to make their introduction more comprehensive and more up to date. For the “Introduction” section, the authors could report the production of hydrogen as clean energy or the production of synthesis gas via the valorization of biogas. There are a lot of research group that have focused their research interest on utilization of biogas.

In general, different processes have been developed for the production of hydrogen, namely,  biogas dry reforming and steam reforming of biogas. Please include some of the following new studies.

 

1.       S. Jung, N.P. Shetti, K.R. Reddy, M.N. Nadagouda, Y.-K. Park, T.M. Aminabhavi, E.E. Kwon, Synthesis of different biofuels from livestock waste materials and their potential as sustainable feedstocks – A review. Energy Conversion and Management 236 (2021) 114038.

2.       M.A. Goula, N.D. Charisiou, G. Siakavelas, L. Tzounis, I. Tsiaoussis, P. Panagiotopoulou, G. Goula, I.V. Yentekakis, Syngas production via the biogas dry reforming reaction over Ni supported on zirconia modified with CeO₂ or La₂O₃ catalysts. International Journal of Hydrogen Energy 42 (2017) 13724-13740.

3.       V.P. Aravani, H. Sun, Z. Yang, G. Liu, W. Wang, G. Anagnostopoulos, G. Syriopoulos N.D. Charisiou, M.G. Goula, M. Kornaros, V.G. Papadakis. Agricultural and livestock sector's residues in Greece & China: Comparative qualitative and quantitative characterization for assessing their potential for biogas production. Renewable and Sustainable Energy Reviews 154 (2022) Article number 111821.

4.       S. Jung, J. Lee, D.H. Moon, K.-H. Kim, E.E. Kwon, Upgrading biogas into syngas through dry reforming. Renewable and Sustainable Energy Reviews 143 (2021) 110949.

5.       Y. Gao, J. Jiang, Y. Meng, F. Yan, A. Aihemaiti, A review of recent developments in hydrogen production via biogas dry reforming. Energy Conversion and Management 171 (2018) 133-155.

 

Comment #2

In the manuscript there are some typos, please correct carefully.

 

Author Response

Dear Reviewer,
On behalf of my team, I would like to thank you for your interest in our work to improve the manuscript.
You will find attached the comments of all the questions and the answers given;
Thanks.

Reviewer #2 Round 2:

Comment #1

The authors need to improve their reference list as they have used only 45 references. I think that they should aim for at least 5 references in order to make their introduction more comprehensive and more up to date. For the “Introduction” section, the authors could report the production of hydrogen as clean energy or the production of synthesis gas via the valorization of biogas. There are a lot of research group that have focused their research interest on utilization of biogas.

In general, different processes have been developed for the production of hydrogen, namely, biogas dry reforming and steam reforming of biogas. Please include some of the following new studies.

1. S. Jung, N.P. Shetti, K.R. Reddy, M.N. Nadagouda, Y.-K. Park, T.M. Aminabhavi, E.E. Kwon, Synthesis of different biofuels from livestock waste materials and their potential as sustainable feedstocks – A review. Energy Conversion and Management 236 (2021) 114038.
2. M.A. Goula, N.D. Charisiou, G. Siakavelas, L. Tzounis, I. Tsiaoussis, P. Panagiotopoulou, G. Goula, I.V. Yentekakis, Syngas production via the biogas dry reforming reaction over Ni supported on zirconia modified with CeO₂or La₂O₃ catalysts. International Journal of Hydrogen Energy 42 (2017) 13724-13740.
3. V.P. Aravani, H. Sun, Z. Yang, G. Liu, W. Wang, G. Anagnostopoulos, G. Syriopoulos N.D. Charisiou, M.G. Goula, M. Kornaros, V.G. Papadakis. Agricultural and livestock sector's residues in Greece & China: Comparative qualitative and quantitative characterization for assessing their potential for biogas production. Renewable and Sustainable Energy Reviews 154 (2022) Article number 111821.
4. S. Jung, J. Lee, D.H. Moon, K.-H. Kim, E.E. Kwon, Upgrading biogas into syngas through dry reforming. Renewable and Sustainable Energy Reviews 143 (2021) 110949.
5. Y. Gao, J. Jiang, Y. Meng, F. Yan, A. Aihemaiti, A review of recent developments in hydrogen production via biogas dry reforming. Energy Conversion and Management 171 (2018) 133-155.

 

Response #1: The references are added to the introduction section of the manuscript are as fellow:

 

1. Jung, S., Shetti, N. P., Reddy, K. R., Nadagouda, M. N., Park, Y. K., Aminabhavi, T. M., & Kwon, E. E. (2021). Synthesis of different biofuels from livestock waste materials and their potential as sustainable feedstocks–a review. Energy Conversion and Management, 236, 114038. Page 1, Jung et al. [1].
2. Jung, S., Lee, J., Moon, D. H., Kim, K. H., & Kwon, E. E. (2021). Upgrading biogas into syngas through dry reforming. Renewable and Sustainable Energy Reviews, 143, 110949. Page 2, Jung et al. [11]
3. Gao, Y., Jiang, J., Meng, Y., Yan, F., & Aihemaiti, A. (2018). A review of recent developments in hydrogen production via biogas dry reforming. Energy Conversion and Management, 171, 133-155. Page 2, Gao et al [10].
4. Charisiou, N. D., Siakavelas, G., Papageridis, K. N., Baklavaridis, A., Tzounis, L., Avraam, D. G., & Goula, M. A. (2016). Syngas production via the biogas dry reforming reaction over nickel supported on modified with CeO2 and/or La2O3 alumina catalysts. Journal of Natural Gas Science and Engineering, 31, 164-183. Page 2, Charisiou et al., [12].
5. VIJAYAKUMAR, Pradeshwaran, AYYADURAI, Saravanakumar, ARUNACHALAM, Kantha Deivi, et al. Current technologies of biochemical conversion of food waste into biogas production: A review. Fuel, 2022, vol. 323, p. 124321. Page 2, Vijayakumar et al [15].

 

Comment #2. In the manuscript there are some typos, please correct carefully.

 

Response #2: we did a comprehensive review of the manuscript and the typos have been corrected.

 

Reviewer 3 Report (New Reviewer)

The manuscript “Hydrolysis of food waste with immobilized biofilm as a pre-treatment method for the enhancement of biogas production” requires improvement. Authors should revise and improve the English language and grammar throughout the manuscript.

 

Include recent articles (2022) in Introduction.

 

Include statistical footnote in Fig.1. Fig.4 and Fig.5

 

Include statistical analysis in Materials and Methods.

 

Unit: Please use mg/g instead of mgg^-1. Use mL instead of ml. Be consistent throughout the manuscript.

 

Include a list of abbreviations in the manuscript.

 

Conclusion should be re-write. It should include the significance of the study and works for future study, not merely repeating the results.

Author Response

Reviewer #3 Round 2

 

The manuscript “Hydrolysis of food waste with immobilized biofilm as a pre-treatment method for the enhancement of biogas production” requires improvement. Authors should revise and improve the English language and grammar throughout the manuscript.

 

Comment #1: Include recent articles (2022) in Introduction.

Response #1: Five recent articles are added to the introduction section. References are cited in the text as the numbers 1, 10, 11 , 12 and 15.

1. Jung, S., Shetti, N. P., Reddy, K. R., Nadagouda, M. N., Park, Y. K., Aminabhavi, T. M., & Kwon, E. E. (2021). Synthesis of different biofuels from livestock waste materials and their potential as sustainable feedstocks–a review. Energy Conversion and Management, 236, 114038. Page 1, Jung et al. [1].
2. Jung, S., Lee, J., Moon, D. H., Kim, K. H., & Kwon, E. E. (2021). Upgrading biogas into syngas through dry reforming. Renewable and Sustainable Energy Reviews, 143, 110949. Page 2, Jung et al. [11]
3. Gao, Y., Jiang, J., Meng, Y., Yan, F., & Aihemaiti, A. (2018). A review of recent developments in hydrogen production via biogas dry reforming. Energy Conversion and Management, 171, 133-155. Page 2, Gao et al [10].
4. Charisiou, N. D., Siakavelas, G., Papageridis, K. N., Baklavaridis, A., Tzounis, L., Avraam, D. G., & Goula, M. A. (2016). Syngas production via the biogas dry reforming reaction over nickel supported on modified with CeO2 and/or La2O3 alumina catalysts. Journal of Natural Gas Science and Engineering, 31, 164-183. Page 2, Charisiou et al., [12].
5. VIJAYAKUMAR, Pradeshwaran, AYYADURAI, Saravanakumar, ARUNACHALAM, Kantha Deivi, et al. Current technologies of biochemical conversion of food waste into biogas production: A review. Fuel, 2022, vol. 323, p. 124321. Page 2, Vijayakumar et al [15].

 

Comments #2: Include statistical footnote in Fig.1. Fig.4 and Fig.5

 

Response #2: The statistical footnotes (error bars) are added in Fig.1. Fig.4 and Fig.5

 

Comment #3: Include statistical analysis in Materials and Methods.

 

Response #3: Sub-section 2.6 is added in the Martials and Methods section for statistical analysis.

 

Comment #4: Unit: Please use mg/g instead of mgg^-1. Use mL instead of ml. Be consistent throughout the manuscript.

 

Response #4: The units of mg/g and mL are used throughout the manuscript.

 

Comment #5: Include a list of abbreviations in the manuscript.

Response #5: A List of abbreviations is added at the biggening of the manuscript right after the ABSTRACT.

Dear Reviewer,
On behalf of my team, I would like to thank you for your interest in our work to improve the manuscript.
You will find attached the comments of all the questions and the answers given;
Thanks

Comments #6: Conclusion should be re-write. It should include the significance of the study and works for future study, not merely repeating the results.

 

Response #6: The conclusion has been improved.

Reviewer 4 Report (New Reviewer)

In this paper, the screened biofilm producer microorganisms were adopted to facilitate the biodegradation of organic compounds and enhance the volume of biogas production. The authors used the statistical method of one-time factor and the response surface method of central composite design to find the optimal values of fixed time, GAC quality and microbial inoculum size. My detailed comments provided below：

1. Keywords: In addition to proper nouns, other keywords should be unified in format.

2. Line48：Change the bold.

3. Line231: Unit error (mgg-1), Please modify the full text.

4. There is no error bar in Table 2. Is parallel measurement done?

5. Figure 3 response surface should be color, please redraw.

6. Is there an error bar in the actual measured value of Table 3 ? Do several sets of parallel measurements?

7. Line 441: The abbreviation should be where the article first appears.

8. Figure 5 has no axes.

9. Figure 6 data without error bars.

10. The reference format is wrong, please modify the format according to the requirements of the journal.

Author Response

Dear Reviewer,
On behalf of my team, I would like to thank you for your interest in our work to improve the manuscript.
You will find attached the comments of all the questions and the answers given;
Thanks

 

In this paper, the screened biofilm producer microorganisms were adopted to facilitate the biodegradation of organic compounds and enhance the volume of biogas production. The authors used the statistical method of one-time factor and the response surface method of central composite design to find the optimal values of fixed time, GAC quality and microbial inoculum size. My detailed comments provided below：

Comments #1: 1. Keywords: In addition to proper nouns, other keywords should be unified in format.

 

Response #1: we used a vocabulary in the keywords to homogenize the words in scientific context.

 

Comments #2:  Line48：Change the bold.

Response #2: The bold at the reference 13 is removed and it is in line 73.

Comments #3: Line231: Unit error (mgg-1), Please modify the full text.

Response #3: The unit mg/g is used throughout the manuscript to be consistent.

 

Comment #4:  There is no error bar in Table 2. Is parallel measurement done?

Response #4: The error bars are added to the data .

 

Comment #5: Figure 3 response surface should be color, please redraw.

Response #5: 3D response surface in Fig 3a has been redraw and the colored on is added.

 

Comment #6: Is there an error bar in the actual measured value of Table 3? Do several sets of parallel measurements?
Response #6: For the data mentioned in table 3 are find from expert design software which gave us figures without errors, but the experiment has been triplicated and the average was considered for the final analysis.

Comment #7: Line 441: The abbreviation should be where the article first appears.
Response #7: The abbreviation is removed from the subtitle and abbreviation list is added at the beginning of the manuscript.

Comment #8: Figure 5 has no axes.
Response #8: Figure 5 is revised to have axes.

Comments #9: Figure 6 data without error bars.
Response #9: Error bars are added in the Figure 6.

Comment #10: The reference format is wrong, please modify the format according to the requirements of the journal.
Response #10: The reference list in the manuscript is reformatted according to the requirement of the journal (a recent article from Sustainability)

Round 2

Reviewer 4 Report (New Reviewer)

It can be published

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

 

Although the authors have indicated where the microbial cultures were taken from, it is not clear what type of microorganims might be part of the consortium and if the consortium has capabilities to be part of an anaerobic digestion system.

 

Section 3.2: It is not clear why the authors cite first results by Fazil et al., 2018. It is not clear if they have followed a similar approach. If this is the case, this should be preferable explained in Materials and Methods. Are the authors giving an example by citing Fazil et al., 2018? It is confusing. Please explain.

 

Section 3.3 explains part of the Methodology followed by the authors. Thus, this paragraph should be placed in the M&M section.

 

Fig. 1: do the results shown in Fig. 1 indicate that the biofilm formed on the support is not reliable after three days of experiment? The figure shows a loss a biomass after 72 hours the experiment has started.

 

Fig. 2: the authors claim that the SEM images show the formation of a biofilm on inoculated tests. The issue with the microscopic technique used is that you rely on only a visual inspection to make such claim. At such zoom of x1,500, you should be able to see already the shape of a microorganism even if there is a biofilm formed by them.

 

Here some examples: 

https://europepmc.org/article/pmc/pmc3648901

https://www.sciencedirect.com/science/article/pii/S1388248111002414

 

Section 3.4: the first paragraph of this section describes a methodology used by the authors. Thus, it should be placed in Materials and Methods.

 

Section 3.5.1: this section is confusing. How can the amount of biofilm grown on a surface be controlled? This is not clearly explained.

 

 

Author Response

Dear Reviewer,
We thank you for your interest in our work.
you will find below all the comments of your remarks and your questions.
Greetings.

 

Section 3.2: It is not clear why the authors cite first results by Fazil et al., 2018. It is not clear if they have followed a similar approach. If this is the case, this should be preferable explained in Materials and Methods. Are the authors giving an example by citing Fazil et al., 2018? It is confusing. Please explain.

 We have added more detail in the material and methods part.

Section 3.3 explains part of the Methodology followed by the authors. Thus, this paragraph should be placed in the M&M section.
We have made the requested corrections
 

Fig. 1: do the results shown in Fig. 1 indicate that the biofilm formed on the support is not reliable after three days of experiment? The figure shows a loss a biomass after 72 hours the experiment has started.

Fig. 2: the authors claim that the SEM images show the formation of a biofilm on inoculated tests. The issue with the microscopic technique used is that you rely on only a visual inspection to make such claim. At such zoom of x1,500, you should be able to see already the shape of a microorganism even if there is a biofilm formed by them.

We have added more detail to explain figures 1 and 2.
 

Section 3.4: the first paragraph of this section describes a methodology used by the authors. Thus, it should be placed in Materials and Methods.

 We have made the requested corrections

Section 3.5.1: this section is confusing. How can the amount of biofilm grown on a surface be controlled? This is not clearly explained.
We have added more detail to explain the control.

Reviewer 2 Report

Authors should check typos and syntax errors.

A better presentation is needed in the conclusions and the link between the text and presented results.

Validation and update is needed of old references.

Also, similarity found at the next source should be reduced

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6133255/

INTERNET 2%

Author Response

Dear Reviewer,
We thank you for your interest in our work.
you will find below all the comments of your remarks and your questions.
Greetings.

 

1. Authors should check typos and syntax errors.

Response- types and syntax errors were checked

2. A better presentation is needed in the conclusions and the link between the text and presented results.

Response-

3. Validation and update is needed of old references. Also, similarity found at the next source should be reduced https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6133255/ INTERNET 2%

Response-

we checked the content of the manuscript

 

Reviewer 3 Report

Undoubtedly, the authors put a lot of work into conducting the research, but the way the results are presented in the article raises concerns. This article requires a lot of revision before publishing in Sustainability. First of all, it is necessary to organize the methodological part and clearly separate the results from the methodology. At the moment, in many places in the result part, there are content clearly related to the methodology that needs to be transferred to the Materials and methods chapter. In the methodical part itself, there is no logical sequence and it is sometimes difficult to see what was done and why. Here are some more detailed comments:

1.      Line 44 - AD abbreviation needs some explanation

2.      The purpose of the research should be more clearly defined.

3.      It seems to me that in the Introduction it is necessary to define more clearly what the authors mean by biofilm.

4.      The methodology is described in an imprecise manner. The terms "a few samples" (line 138) or "many runs" (line 152) used herein are imprecise.

5.      Line 71 - the abbreviation IIUM needs an explanation

6.      Line 87 - please change the units throughout the text, e.g. replace 1 kg / L with 1 kg L^-1

7.      Lines 87-91 - the description is too general

8.      Line 95 - LB abbreviation needs an explanation

9.      Line 108 - SEM abbreviation needs an explanation

10.   Line 110 - please provide more details on the filter used

11.   Line 131 - "several studies" requires reference to the literature

12.   Line 146 - is a bracket before GAC needed?

13.   Line 148 - DOE abbreviation needs some explanation

14.   Line 156 - Table 2.1 or Table 1?

15.   Lines 162-165 - too general description

16.   Line 170 - please delete (Kiran et al., 2015)

17.   Lines 174-177 - the description is too general

18.   Table 2 - All abbreviations used in the table require an explanation under the table

19.   Table 2 - please explain the lack of results for semi-solid

20.   Table 2 - please explain how the VS / TS ratio was calculated

21.   Line 193 - why is the COD in parentheses?

22.   Line 198 - As I understand collected FW corresponds to semi-solid in table 2. At least that's what lines 188-189 show. If this is the case, why do the authors write low pH of the collected FW if there is no pH value in the table.

23.   Lines 196-200 - this part requires reference to the literature

24.   Subchapter 3.2 - I do not understand whether the content presented here applies to the research described in the article or the research of Fazil et al. If it concerns the reviewed article, it should probably be in the methodology. However, this description should be extended to include issues related to enzymes.

25.   Section 3.3 - Why is it in the Results section? This should probably also be included in the methodology.

26.   Subsection 3.3.1 - please organize and leave only what is actually the result.

27.   Subchapter 3.3.2 - please arrange and leave only what is actually the result.

28.   Lines 268-272 - please edit

29.   Subchapter 3.4 - please arrange and leave only what is actually the result. What concerns what was done during the research, please transfer to the methodology

30.   Subchapter 3.5 - please transfer to the methodology

31.   Line 375 - please describe the reactor parameters in detail

32.   Subchapter 3.5.1 - please arrange and leave only what is actually the result. What concerns what was done during the research, please transfer to the methodology

33.   Figure 5 - please correct the value on the vertical axis (separator)

34.   Subchapter 3.5.3 - please reformat

35.   Figure 6 - Please remove 4g

36.   References - please follow the Instructions for authors. Besides, please correct the citation throughout the text and change eg. Zhang et al. (2005) [24] on Zhang et al. [24].

Author Response

Dear Reviewer,
We thank you for your interest in our work.
you will find below all the comments of your remarks and your questions.
Greetings

 

1. Line 44 - AD abbreviation needs some explanation

Response- the anaerobic digestion (AD) has been explained. Line 44

2. The purpose of the research should be more clearly defined.  

 Response-The purpose of the research was clearly defined in the last part of introduction Line 54-81.

3. It seems to me that in the Introduction it is necessary to define more clearly what the authors mean by biofilm.

Response- in the introduction, biofilm was well defined in line 54-60

4. The methodology is described in an imprecise manner. The terms "a few samples" (line 138) or "many runs" (line 152) used herein are imprecise.

Response- few samples and many runs has been removed (line 152 and line 165)

5. Line 71 - the abbreviation IIUM needs an explanation

Response- The abbreviation IIUM has been explained in line 85

6. Line 87 - please change the units throughout the text, e.g. replace 1 kg / L with 1 kg L^-1

Response- the unit 1 kg / L was replaced of the line 87 has been changed and it is in line 101

7. Lines 87-91 - the description is too general

Response- The description has been detailed (line 101-109)

 

8. Line 95 - LB abbreviation needs an explanation

Response-:LB abbreviation has been explained as Luria-Bertan (Line 108)

9. Line 108 - SEM abbreviation needs an explanation

Response- SEM abbreviation has been explained as scanning electronic microscopic (line 121)

 

10. Line 110 - please provide more details on the filter used

Response-The filter used has been detailed on line 159

11. Line 131 - "several studies" requires reference to the literature

Response- References to the literature has been added line 180

12. Line 146 - is a bracket before GAC needed?

Response- it was a control (GAC without biofilm producing bacteria)

 

13. Line 148 - DOE abbreviation needs some explanation

Response- DOE abbreviation was explained (line 142)

14. Line 156 - Table 2.1 or Table 1?

Response-Table 1(line 170)

15. Lines 162-165 - too general description

Response- Some description has been added to that paragraph (line 2019-227)

16. : Line 170 - please delete (Kiran et al., 2015)

Response-: Kiran et al., 2015 has been deleted (line 184)

17. Lines 174-177 - the description is too general

Response- The description is explained in line 101-109

18. Table 2 - All abbreviations used in the table require an explanation under the table

Response- The abbreviations used in table 2 has been explained (line202-line 203)

19. Table 2 - please explain the lack of results for semi-solid

Response- the lack of results for semi-solid of the table 2 was explained under the table (lin 274)

20. Table 2 - please explain how the VS / TS ratio was calculated

Response- in the table 2, VS/TS value has been verified, (VS (%))/ (TS (%)) *100

21. Line 193 - why is the COD in parentheses?

Response-: the parentheses has been removed (line 209)

22. Line 198 - As I understand collected FW corresponds to semi-solid in table 2. At least that's what lines 188-189 show. If this is the case, why do the authors write low pH of the collected FW if there is no pH value in the table.

Response-: pH of the collected food waste has been replaced by pH of the prepared food waste (line 214)

23. Lines 196-200 - this part requires reference to the literature

Response-Reference was added to this part

24. Question 25: Subchapter 3.2 - I do not understand whether the content presented here applies to the research described in the article or the research of Fazil et al. If it concerns the reviewed article, it should probably be in the methodology. However, this description should be extended to include issues related to enzymes.

Response- Yes, the content presented here applies to the research described in the article or the research of Fazil et al., (2018). This section has been transferred to the methodology section 2.1

25. Section 3.3 - Why is it in the Results section? This should probably also be included in the methodology.

Response-This section was reduced and added to the methodology (line 104-108)  

26. Subsection 3.3.1 - please organize and leave only what is actually the result.

Response-

27. Subchapter 3.3.2 - please arrange and leave only what is actually the result.

Response-one paragraph was transferred to methodology (line 156-160) and only figure explanation was left on the subchapter 3.3.2

28. Lines 268-272 - please edit

Response-edited and transferred to methodology (line 156-161)

29. Subchapter 3.4 - please arrange and leave only what is actually the result. What concerns what was done during the research, please transfer to the methodology

Response- The subchapter 3.4 was reduced and some sentences were transferred to section 2.4.2 line 234-239

30. : Subchapter 3.5 - please transfer to the methodology

Response- The paragraph of the subchapter 3.5 has been transferred to subchapter 2.41 of the methodology (line 187-201)

31. Line 375 - please describe the reactor parameters in detail

Response- reactor parameters were descripted in detail in section 2.1 (line 97-109)

 

32. Subchapter 3.5.1 - please arrange and leave only what is actually the result. What concerns what was done during the research, please transfer to the methodology

Response- One paragraph of the section 3.5.1 which is related to methodology has been transferred to methodology part section 2.4.1

 

33. Figure 5 - please correct the value on the vertical axis (separator)

Response-

34. Subchapter 3.5.3 - please reformat

 Response-subchapter 3.5.3 has been reformated

35. Figure 6 - Please remove 4g

Response-4g has been removed from the figure 6

36. References - please follow the Instructions for authors. Besides, please correct the citation throughout the text and change eg. Zhang et al. (2005) [24] on Zhang et al. [24].

Response- All the citation were corrected throughout the text

Reviewer 4 Report

The introduction should end with a clearly stated research goal.

Vague phrases should be avoided. For example Line 87: "To characterize the collected FW, some analyzes such as" give exactly those analyzes that were performed without appending such as. 

The description in the chapter Measurement of attached biofilm on GAC should be corrected. line 111. 

Figure 2 requires a definite improvement in the form of arrows showing the elements discussed. In its present form, it is difficult to read the described structures. 

Figure 4 is very unreadable. the marking of individual columns is difficult to read. Please refer to all studies performed in your conclusions, for example, no reference to the SEM photos.

The submitted comments are of an orderly nature, and the overall research was well-planned and carried out.

Author Response

Dear Reviewer,
We thank you for your interest in our work.
you will find attached all the comments of your remarks and your questions.
Greetings.

 

1. The introduction should end with a clearly stated research goal.

      Response- The introduction was stated well (Line 54 to 81)

2. Vague phrases should be avoided. For example Line 87: "To characterize the collected FW, some analyzes such as" give exactly those analyzes that were performed without appending such as. 

      Response- Vague phrases has been reduced (Line 101)

3. The description in the chapter Measurement of attached biofilm on GAC should be corrected. line 111. 

Response- The description in the chapter Measurement of attached biofilm on GAC was corrected (line 124)

4. Figure 2 requires a definite improvement in the form of arrows showing the elements discussed. In its present form, it is difficult to read the described structures. 

Response 4-

5. Figure 4 is very unreadable. the marking of individual columns is difficult to read. Please refer to all studies performed in your conclusions, for example, no reference to the SEM photos.

Response 5-The structure for Figure 4 has been changed (Line 432). And the reference for SEM was added (Line 308).

Round 2

Reviewer 1 Report

The topic is indeed of relevance for the scientific community.

However, Ido not see my comments/questions have been properly answered.

For example, there is still not enough experimental evidence of biofilm formation in the SEM pictures used in the manuscript.

Due to the format used by the authors to provide a Response to reviewers comments, it is not easy no discern of the authors have properly improved their paper.

The authors have mainly included these type of sentences but is not clear where corrections have been made in the manuscript and how corrections were made:

-We have added more detail in the material and methods part.

-We have added more detail to explain figures 1 and 2.

-We have made the requested corrections

-We have added more detail to explain the control.

Author Response

Dear reviewer,
following the questions and remarks proposed after your reading of our manusript. You will find attached the answers and the requested corrections.
In a favorable result, please accept Sir my sincere greetings.

Author Response File: Author Response.pdf

Reviewer 3 Report

Unfortunately, I suggest to reject the article. Mainly because of the way the article was improved. When responding to comments, the authors indicate the places where the corrected part of the text is supposed to be, but in reality, the amendments are in a completely different place, eg the answer to comments 4 and 5. This also applies to other comments. In this situation, checking what and how the authors corrected is sometimes impossible. In addition, some comments were not taken into account, eg comments 6, 33 and 36. In response to my comment number 24 they actually moved chapter 3.2 to 2.1. However, they forgot to delete 3.2, so at the moment there are two identical paragraphs, one in the methodology (lines 83-100) and one in Results (lines 288-304). The same is true for comment 27. The list of publications still does not comply with the Instructions for authors.

Author Response

Dear reviewer,
following the questions and remarks proposed after your reading of our manusript. You will find attached the answers and the requested corrections.
In a favorable result, please accept Sir my sincere greetings.

Author Response File: Author Response.pdf

Round 3

Reviewer 1 Report

The current manuscript is based on assuming that a biofilm is capable of functioning as a pretreatment method for the enhancement of biogas production.

There is not enough evidence that a biofilm is even developed in the support selected by the authors.

 

Author Response

Dear Reviewer,
We have received your comments about our manuscript.
you will find attached the answers to all the remarks.
In a favorable result please accept my sincere greetings.

Author Response File: Author Response.pdf

Reviewer 3 Report

This time the authors took into account most of my comments, although it is still difficult to find their corrections in the text. Besides, there are still some things that need to be corrected, e.g. notation of the unit in lines 374, 377 and in the title of the Y axis in figures 4, 5 and 6. The correct way of explaining the abbreviations under table 2 should also be used. In the references, in most cases there are no abbreviations for journal titles.

Author Response

Dear Reviewer,
We have received your comments about our manuscript.
you will find attached the answers to all the remarks.
In a favorable result please accept my sincere greetings.

Author Response File: Author Response.pdf