Biogas Potential from Slums as a Sustainable and Resilient Route for Renewable Energy Diffusion in Urban Areas and Organic Waste Management in Vulnerable Communities in São Paulo

Round 1

Reviewer 1 Report

Line 84: What do the authors mean by these systems? Biogas systems or solar and wind systems?

Please use a better and higher resolution image for Figure 1. The details are not clearly visible upon zooming in.

Line 143: Need to expand on biogas storage options and use citations. Quantify or explain 'flexible and relatively cheap energy storage' or cite data that supports this statement.

Line 204: Why was 40% efficiency chosen for the calculations? Provide data or evidence supporting this assumption.

There is definitely useful data in the manuscript, but my main concern is the applicability of this data presented as a journal article instead of a white paper or a report. I am not sure if it contains enough of an in-depth study of the bioelectricity potential from biogas in Sao Paolo. The article seems very limited in its focus and outlook

Author Response

Dear reviewer 1,

Thank you so much for the review of our paper. We appreciate the careful reading of the work and the suggestions to improve it. You can find a response for you comments in the attached document.

 

Thank you.

Author Response File: Author Response.pdf

Reviewer 2 Report

Title: Bioelectricity Potential From Biogas in Slums to Renewable Energy Diffusion in Urban Areas: A Sustainable and Reliable  Route for Organic Waste Management and Bioenergy Generation in Vulnerable Communities

Brief summary

The present study aimed to demonstrate the feasibility of producing bioelectricity from the biogas obtained through the anaerobic digestion of the 400.000 tons of food waste generated in São Paulo’s slums, the largest city in Latin America. Specifically, this paper is aimed  to i) determine and map the biogas potential of the OFMSW in slums in the city of São Paulo, ii) calculate its bioelectricity potential, iii) calculate the environmental impact of the waste mismanagement, and iv) discuss the integration of this renewable energy source (RES) into the local energy matrix.The results show a bioelectricity potential of up to 135,780.76 MWh/y, which could represent 6% of São Paulo's electricity demand with an associated potential reduction of 1,816.18 Gg/y of CO2eq.

• the manuscript is relevant but it is not presented in well structured manner.
• most references in this manuscript are mostly within the last five years, but it needs revision for consistency
• the research design is not explained  and it is not clear how the hypothesis was tested and data collection technique/instrument is not mentioned in this manuscript.
• some figures (fig 1. and fig.3) do not properly show the data and  they are not easy to interpret and understand the data.
• the data in the tables (table 2) are not interpreted appropriately and consistently throughout the manuscript.
• the title is broad and it must be specific to the study area.
• what is the economic benefits for the population in slum and also in the city as the whole by using waste for biogas and electricity?
• the statements and conclusions drawn are not coherent and supported by the listed citations.
• what are the main waste sources considered for this research?
• what are the existing technologies that use for converting waste into energy in Sao Paulo city? is there an existing/installed anaerobic digester in sao paulo to convert wastes into bio-electricity, if yes? how much energy is generated? what are the main source of wastes that are used for energy production and what is the main contribution from this manuscript?
• there is a very good review article about the Economic Potential of Untreated Household Solid Waste (HSW) in the City of São Paulo published by Sustainability journal (https://www.mdpi.com/2071-1050/12/13/5249/htm), but the authors did not used it as a reference for this article
• recently there is one similar article published by energies in 2022 particularly in Sao Paulo (https://doi.org/10.1016/j.energy.2021.122326) and it is not clear what the current article presents different information. Can the authors explain what is the new knowledge they investigated?

Specific comments:

1. Abstract:

• In the abstract, there is a lack of concise explanation about the methodology and data analysis of the research.
• In addition, from line 17-20, it says that "..... This potential was previously studied on lab-scale and then expanded to the whole municipality, mapped, and discussed regarding the environmental impact of waste mismanagement and the renewable energy  source (RES) integration into the local energy system." However, there is no any explanation about the lab scale data in the literature review nor in the data analysis"
• what is the new knowledge/information that this manuscript contributed if it is already studied in the lab scale and expanded throughout the city??

2. Introduction

• There are typos and English language must be double checked
• The literature review is not comprehensive and of the research  gap is not well articulated.
• the quality of Fig.1. could be improved.

3. methodology

• the paragraph from line 175 to 178 is not clear. Re-phrase it. what are 9.7% households in slums, 0% in the richest and 69.5% in the poorest???
• Research design :-

Research design is vague. it is not clear, how did you generate data? where did you get the primary data? Did you generate data by doing experiment or by filed survey and distributing questionnaires?  Data analysis is okay, but data collection method is completely not clear. must be corrected.

3. Results

• From line 229, it says ".........inhabitants living in slums, it is estimated to be a generation of 399,819.49 t/y of OFMSW" is it kg/year or tone/year ? Check it again
• Table 2: the calculations in column 2 is not clear. How was the calculation? or give precise explanation under the table 2.
• The numbers (for Total OFMSW CO2eq emissions (Gg/y), Total CO2eq emissions, and Total OFMSW generation (t/y) ) in the text and in table 2 are completely different (please check it again and for consistency, the units must be similar in the text as well as in table 2).

 

4. Conclusion:

 

• In the conclusion it says that (line 302-306) ".....This study aims to discuss the importance of a better look into the community that is especially suffering from waste mismanaging and, often, low-quality energy, besides the direct consequences of the state of energy poverty present in these   However, the whole society can benefit from the services and products delivered by the biogas technology." this conclusion is not supported by data and evidence! what are your evidence or data that lead the authors to conclude this.?

5. references

• Writing references are not consistence, some references are not fully written like ref. 26 (no publisher name, volume No_, page)

Author Response

Dear reviewer 2,

Thank you so much for the review of our paper. We appreciate the careful reading of the work and the suggestions to improve it. You can find a response for you comments in the attached document.

 

Thank you.

Author Response File: Author Response.pdf

Reviewer 3 Report

The topic addressed in the paper "Bioelectricity Potential From Biogas in Slums to Renewable Energy Diffusion in Urban Areas: A Sustainable and Reliable Route for Organic Waste Management and Bioenergy Generation in Vulnerable Communities" proposed for publication by D'Aquino et al. is extremely interesting and not often addressed in the literature. The authors provide a lengthy review of the issues and potential of biogas production from food waste. However, the article, in the proposed version, suffers from a very large number of flaws that need to be corrected before it can be published.

- The title contains redundant information; I would propose to simplify it to "Potential Biogas in Slums to Renewable Energy Diffusion in Urban Areas: A Sustainable and Reliable Route for Organic Waste Management in Vulnerable Communities".

- In the abstract lines 16 and 17 : ... the 400.000 tons of food waste generated in Sao Paulo..." must replaced by "... the 400,000 tons of food waste generated yearly in Sao Paulo..." Please note the comma in 400,000

- The introduction is far too long and some paragraphs seem unhelpful to the development of the body of the article, lines 65-83, 90-101, 126-140 could be deleted without impacting the scientific content of the article.

- Many figures are given with an unnecessary or even laughable number of decimal places, given the uncertainties. The figures given, for example, in lines 21, 22, 166, 171, 229, 230, 243, 245, 256, 298, and in Table 2 should be rounded.

- Some figures are inconsistent: 1,816.18 (which should be rounded to 1,82) Gg/y of CO2 eq in lines 22 and 243, while line 252 mentions 1,780, and line 297 1,800.

- The calculation of the number of tons of CO2 avoided is incomplete. The authors mention values ranging from 0.96 to 20.04 kgCO2/tonne of food waste, which gives, for 399,819 tonnes of food waste (line 229) a range of 386 to 8,016 Gg/y of CO2 eq. How do the authors arrive at the average value of 1,780 Gg/y of CO2 eq? This last value refers to a value of 4.45 kgCO2/tonne of food waste. And finally, given the huge range (0.96 to 20.04), should we not give a range of results for potential CO2 avoided?

- It would then be interesting to discuss the cost of such an anaerobic digestion plant and the obstacles that could limit its installation

- The authors discuss in terms of methane production converted into electricity and calculated in CO2 equivalent avoided. What about the heat released by the CHP, is it also recoverable?

- Finally, many references refer to texts in Portuguese, which should be deleted, as they are only understandable by a limited number of readers worldwide and are often inaccessible (ref 14, 15, 26, 27, 30, 31, 33, 34)

Author Response

Dear reviewer 3,

 

Thank you so much for the review of our paper. We appreciate the careful reading of the work and the suggestions to improve it. You can find the response for your comments in the attached document.

 

Thank you.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The manuscript has been improved, but needs some more work, in my opinion.

Title could be improved further. The first sentence is not grammatically correct.

Abstract: 400,000 tons or 400 tons?

Information in Line 216 - 218 seems to be repeated in Lines 231 - 234. Could it be combined together?

Lines 754 - 762: Just to clarify, 435,000 t/y of OFMSW was generated in the slums of Sao Paulo, and 1.7 million t/y of OFMSW was mismanaged, but that was from the entire city, not just the slums. Correct? The way it's currently written is a little confusing. Perhaps, it could be restructured for enhanced comprehension?

Why use 1.7 million in line 776 and not on line 757. Please be consistent with data presentation, and significant figures.

Is it possible to improve Fig 3 by showing where the slums are? The figure caption says bioelectricity potential from Sao Paulo's slums, but it's hard to tell where the slums are, unless you go back to Fig 1, which is not as detailed on the district divisions.

While I do like the idea of using digesters for energy generation from OFMSW, I think the authors could improve on the argument for digesters for bioelectricity production. For example, economic benefits in $? Meeting 6% energy demand sounds great, but could it be cheaper/more sustainable to rely on some other means of energy production? Could you discuss other benefits of using a digester or perhaps, the possibility of a biorefinery? As you mentioned, large scale production is more cost effective here, so a community project would be more ideal, and a potential biorefinery to generate not only biogas, but other valuable products as well? Digestion could be a pathway to those valuable products. 

There are a few confusing and incomplete sentences throughout the manuscript, e.g. Incomplete sentence, Line 1139. such as large....?? Please make the relevant changes, as needed. 

Author Response

Dear reviewer 1,

Thank you so much for the quick second review of our paper. I’ve double-checked the English and tried to incorporate as much as possible all the suggestions. Please find attached our response to your comments.

Thanks,

Camila.

Author Response File: Author Response.pdf

Reviewer 2 Report

The Authors substantially improved the article. 

However, there are some points to be checked again in the revised manuscript during proof reading. The reference style is not still consistent, some references have volume, page number ....etc but other do not have. It should be consistent.

Author Response

Dear reviewer 2,

Thank you so much for the quick second review of our paper. I’ve double-checked the English and tried to incorporate as much as possible all the suggestions. So please find attached our response to your comments.

Camila.

Author Response File: Author Response.pdf

Reviewer 3 Report

Still some remarks to be correctly answered, please see my comments written in blue in the joined file

Comments for author File: Comments.pdf

Author Response

Dear reviewer,

Thank you so much for your quick review. Of all the 51 references, 6 are in Portuguese, and they are all key publications for this paper. Unfortunately, there are no replacements for these publications. I rechecked the citations, the ones from journals are complete. A few publications are not from journals, but I tried to complete as much as possible. 

Hope that you understand the decisions.

Camila.