A Simple Methodology for Estimating the Potential Biomethane Production in a Region: Application in a Case Study
Round 1
Reviewer 1 Report
Dear Authors,
Thank you for this nice method paper focused on the estimation of the biomethane production potential in Spain. Please find my detailed comments below. In general, I would strongly recommend to discriminate upgrade of biogas to natural gas with purification of biogas to natural gas. As of today status, power to gas technologies have reached the market and the European union gave strong signs about its relevance with investment in companies proposing such solutions. Hence, even if your study is mainly focusing on raw biogas purification methods to biomethane to estimate the overall methane potential from available wastes, it would be beneficial to introduce also biogas upgrade as an approach (not only purification = removal of CO2/H2S).
As minor comments, review figures and tables such as figure 3. The figure name should be revised from an English formulation point of view and could be changed e.g. in the following direction à Market shares of the different biogas purification approaches available in the market.
In tables always add units even if "potentially trivial". As an example; biogas purity in Vol.% (not only % which could be theoretically also a mass %) to give all the necessary information in a single sight to the table numbers without needing to go back in the method section to verify / be sure.
Finally, for the conclusion you identified that even without upgrading the CO2 fraction you will reach a high replacement of natural gas import in Spain.
To strengthen the outlook of your discussion (depending on how you integrate my above comments on the power to gas upgrading route), how would the picture look like with a power to gas biomethane production? The relative share could almost double and this could further strengthen further your research outcome/message delivery.
Here are few citations to introduce the concept of upgrading vs purification of raw biogas using efficient power to gas process solution (e.g. chemical methanation and biological methanation).
M. Thema, F. Bauer, M. Sterner, Power-to-Gas: Electrolysis and methanation status review, Renewable and Sustainable Energy Reviews, Volume 112, 2019, Pages 775-787, ISSN 1364-0321, https://doi.org/10.1016/j.rser.2019.06.030.
Bernacchi, S., Weissgram, M., Wukovits, W., and Herwig, C., Process efficiency simulation for key process parameters in biological methanogenesis, AIMS Bioeng., Volume 1, Number 1, 2014, pp. 53–71
Bob van der Zwaan, Remko Detz, Nicole Meulendijks, Pascal Buskens, Renewable natural gas as climate-neutral energy carrier?, Fuel, Volume 311, 2022, 122547, ISSN 0016-2361, https://doi.org/10.1016/j.fuel.2021.122547.
Bellini, R.; Bassani, I.; Vizzarro, A.; Azim, A.A.; Vasile, N.S.; Pirri, C.F.; Verga, F.; Menin, B. Biological Aspects, Advancements and Techno-Economical Evaluation of Biological Methanation for the Recycling and Valorization of CO2. Energies 2022, 15, 4064. https://doi.org/10.3390/en15114064
Author Response
Dear Authors,
Thank you for this nice method paper focused on the estimation of the biomethane production potential in Spain. Please find my detailed comments below. In general, I would strongly recommend to discriminate upgrade of biogas to natural gas with purification of biogas to natural gas. As of today status, power to gas technologies have reached the market and the European union gave strong signs about its relevance with investment in companies proposing such solutions. Hence, even if your study is mainly focusing on raw biogas purification methods to biomethane to estimate the overall methane potential from available wastes, it would be beneficial to introduce also biogas upgrade as an approach (not only purification = removal of CO2/H2S).
Thank you very much for your interesting comments and recommendations, which have improved the manuscript. We also appreciate the time devoted to our paper. We find very interesting this recommendation about biogas upgrading and biogas purification. We have clarified the difference between both concepts, both in the introductory part and the methodology and results.
We have introduced biogas upgrade and power to gas technologies.
As minor comments, review figures and tables such as figure 3. The figure name should be revised from an English formulation point of view and could be changed e.g. in the following direction à Market shares of the different biogas purification approaches available in the market.
Thank you very much for this observation. We have reviewed figure and tables names, and they have been revised following your proposal.
In tables always add units even if "potentially trivial". As an example; biogas purity in Vol.% (not only % which could be theoretically also a mass %) to give all the necessary information in a single sight to the table numbers without needing to go back in the method section to verify / be sure.
Thank you very much for this observation. We have added Vol. % and mass % units in every table we consider it is necessary.
Finally, for the conclusion you identified that even without upgrading the CO2 fraction you will reach a high replacement of natural gas import in Spain.
To strengthen the outlook of your discussion (depending on how you integrate my above comments on the power to gas upgrading route), how would the picture look like with a power to gas biomethane production? The relative share could almost double and this could further strengthen further your research outcome/message delivery.
Here are few citations to introduce the concept of upgrading vs purification of raw biogas using efficient power to gas process solution (e.g. chemical methanation and biological methanation).
Thema, F. Bauer, M. Sterner, Power-to-Gas: Electrolysis and methanation status review, Renewable and Sustainable Energy Reviews, Volume 112, 2019, Pages 775-787, ISSN 1364-0321, https://doi.org/10.1016/j.rser.2019.06.030.
Bernacchi, S., Weissgram, M., Wukovits, W., and Herwig, C., Process efficiency simulation for key process parameters in biological methanogenesis, AIMS Bioeng., Volume 1, Number 1, 2014, pp. 53–71
Bob van der Zwaan, Remko Detz, Nicole Meulendijks, Pascal Buskens, Renewable natural gas as climate-neutral energy carrier?, Fuel, Volume 311, 2022, 122547, ISSN 0016-2361, https://doi.org/10.1016/j.fuel.2021.122547.
Bellini, R.; Bassani, I.; Vizzarro, A.; Azim, A.A.; Vasile, N.S.; Pirri, C.F.; Verga, F.; Menin, B. Biological Aspects, Advancements and Techno-Economical Evaluation of Biological Methanation for the Recycling and Valorization of CO2. Energies 2022, 15, 4064. https://doi.org/10.3390/en15114064
Thank you very much for this recommendation and for the references given. We have included three of them in the article ([6], [7], [9]) to introduce power to gas technologies, and we have cited another [8] to mention that it could be possible to duplicate biomethane production. We also talk about it in the conclusion. Nevertheless, although we name them, we have not applied it in the methodology because we considered only purification processes. Finally, as a conclusion, we indicate it would be interesting to consider power-to-gas technologies in a future line of the article.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
1. The subject of the article is very interesting.
2. The article lacks methodology. The Authors should definitely describe it in detail step by step.
3. Line 76-89. These four points of the methodology should be listed and described in more detail.
4. Fig. 2. Reverse 180 degrees and rename it as an algorithm.
5. Fig. 3. English in the description.
6. Results. In Tab. 1 there are only types of bio-waste. How do you know how much of them there were? How was the biogas production potential estimated? Estimation is done based on a mathematical formula. There is no mathematical formula in this work. It is not known how the Authors obtained the results.
7. Tab. 6. What units are the data in? Are these results of the Authors, or are they data from the literature?
8. The summary should be rewritten after the change in methodology. You should write whether this methodology was useful after applying it to a specific example.
Author Response
- The subject of the article is very interesting.
Thank you very much for this comment, we appreciate the time devoted to our paper.
- The article lacks methodology. The Authors should definitely describe it in detail step by step.
Thank you very much for this suggestion. The methodology has been briefly described at the beginning of point 2. Methodology. After that, each step is described in detail.
- Line 76-89. These four points of the methodology should be listed and described in more detail.
Thank you for this recommendation. The four points you mention have been listed and briefly described.
- Fig. 2. Reverse 180 degrees and rename it as an algorithm.
Fig. 2 has been reversed 180 degrees and renamed as an algorithm.
- Fig. 3. English in the description.
Thank you very much for this observation. English is used in the description and technologies have been renamed.
- Results. In Tab. 1 there are only types of bio-waste. How do you know how much of them there were? How was the biogas production potential estimated? Estimation is done based on a mathematical formula. There is no mathematical formula in this work. It is not known how the Authors obtained the results.
Thank you for this comment. In Tab. 1 different types of biowaste are characterized according to the scientific literature. The estimation criteria are described during the methodology. We have added a previous formula to Tab. 1 to make it clearer (line 233)
- Tab. 6. What units are the data in? Are these results of the Authors, or are they data from the literature?
Thank you very much for this observation. We have added units in the table: ton/year. We have also indicated a formula showing the calculus performed to obtain the biomethane potential production (line 356)
- The summary should be rewritten after the change in methodology. You should write whether this methodology was useful after applying it to a specific example.
Thank you very much for your comment. It has been really useful to improve the methodology section. Based on this, the summary has also been modified. The proposed methodology has been successfully applied to the case study, which has allowed us to corroborate its validity. Its application has made it possible to obtain results for the Spanish case and to estimate the total potential for obtaining biomethane from the organic waste produced in Spain.
Author Response File: 
Author Response.docx
Reviewer 3 Report
In this paper, the authors estimated the potential biomethane production in Spain from different biomasses by data found in scientific literature. The authors aimed at proposing a methodology for this estimation. Nevertheless, this methodology is not innovative or scientifically relevant.
The introduction is very short, without an adequate background investigation. Which is the novelty of this work? The objective is clear but literature is widely full of works about the biomethane potential of several biomasses, included those studied in the submitted paper!
Moreover, extensive editing of English language and style are required. The paper needs a wide revision from an English speaker, because it is evident a sort of literal translation from Spanish to English. From the writing style point of view, sentences are too long and reading is not fluid. Finally, just some revisions are shown below as examples:
ABSTRACT
Please, substitute “to reduce the use of fossil fuels and minimise the biowaste finally disposal into landfills” with “the reduction of the use of fossil fuels and the minimization of the final biowaste disposal into landfills”
INTRODUCTION
Line 36: “will be able to BE PRODUCED…”
Line 87: “depending ON”
Line 108: “It is because to obtain them”
Line 132: “does noT guarantee”
Line 246: “co-substrates systems requires”
For this reasons, this papers is not suitable to be published in a scientific journal in this form.
Author Response
In this paper, the authors estimated the potential biomethane production in Spain from different biomasses by data found in scientific literature. The authors aimed at proposing a methodology for this estimation. Nevertheless, this methodology is not innovative or scientifically relevant.
Thank you very much for your revision, we appreciate the time devoted to our paper. We have included some changes in the manuscript, to improve it, according to the comments from the other reviewers.
The introduction is very short, without an adequate background investigation. Which is the novelty of this work? The objective is clear but literature is widely full of works about the biomethane potential of several biomasses, included those studied in the submitted paper!
Thank you. The objective of the article is to propose a simple methodology, applicable to any geographical area. To test its validity, it has been successfully applied to the Spanish case study, which demonstrates its applicability.
We have included additional information in the introduction and in the methodological part, according to the comments of other reviewers, to improve the manuscript.
Moreover, extensive editing of English language and style are required. The paper needs a wide revision from an English speaker, because it is evident a sort of literal translation from Spanish to English. From the writing style point of view, sentences are too long and reading is not fluid. Finally, just some revisions are shown below as examples:
ABSTRACT
Please, substitute “to reduce the use of fossil fuels and minimise the biowaste finally disposal into landfills” with “the reduction of the use of fossil fuels and the minimization of the final biowaste disposal into landfills”
INTRODUCTION
Line 36: “will be able to BE PRODUCED…”
Line 87: “depending ON”
Line 108: “It is because to obtain them”
Line 132: “does noT guarantee”
Line 246: “co-substrates systems requires”
For this reasons, this papers is not suitable to be published in a scientific journal in this form.
Thank you very much for these comments. The English has been reviewed by the publisher's English editing service (MDPI Language Editing Services)
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Now, it is O.K.
Author Response
Thank you very much!
Reviewer 3 Report
After the significant revision made by the authors, the paper can be now accepted for publication
Author Response
Thank you ver y much!
