Waste-to-Energy Pipeline through Consolidated Fermentation–Microbial Fuel Cell (MFC) System

Round 1

Reviewer 1 Report

Processes     waste treatement

K. Kumar and M-H. Chen

July 2023

 

General comment

This review is interesting although not fully equilibrated in its presentation. The second part detailing some results is sometimes poor in explanations and comments on the interest/quality of cited works is often missing. The English writing is not always perfect, strange situation for people staying in the US.

When using various processes/methods and different waste feeds to obtain added value products, there is always a solid residue, enriched with refractory materials and often high toxicity. Reviewer thinks useful that a special section must be devoted to this problem: the authors made a limited comment on such a situation (see Lines 432-436).

 

Detailed comments

In different pages % numbers are given (for example in Lines 130-131): Do the values refer to wt% or volume %? In all the text such information may appear.

Line 177: the starting material is labelled MSWC in the Figure (Is C used for Composition?). Why rubber has been considered as non-combustible?

Line 204: define what is “XOS”

Line 274: “heart valves”: quite specific – needs explanation.

Figures 4 and 5 were not introduced in the text.

In Table 1, Power Output is expressed in different units such as V, mW/m2 or mW/m3, W/m2. For true comparison, it seems useful to try to present all results with the same unit, or present equations allowing conversion.

Line 584: “of m/Wm2 » : to be corrected.

Lines 599 - 601: “as KmnO4 » : maybe KMnO4.

Lines 633-637: Can the authors speculate on the reasons inducing such differences?

Line 678: “from waste material using through WTE pathways could be”: what does this mean?

The writing needs a serious revision

Author Response

This review is interesting although not fully equilibrated in its presentation. The second part detailing some results is sometimes poor in explanations and comments on the interest/quality of cited works is often missing. The English writing is not always perfect, strange situation for people staying in the US.

We thank you for your comments. As suggested, all the revisions have been made in the revised manuscript. Details of the changes made are outlined below. As suggested by the reviewer, English have been also revised in the revised manuscript.

When using various processes/methods and different waste feeds to obtain added-value products, there is always a solid residue, enriched with refractory materials and often high toxicity. Reviewer thinks useful that a special section must be devoted to this problem: the authors made a limited comment on such a situation (see Lines 432-436).

We thank the reviewer for the comment and suggestion. There are always solid residues or byproducts generated when using various processes/methods to convert municipal solid waste (MSW) and agriculture residues into value-added products. The characteristics and composition of the residues vary depending on the complexity of the waste and the types of methods being used for conversions. The composition and characteristics of the solid residues also vary depending on several factors such as population, location, and waste management practices. There are multiple factors affecting the quality and quantity of products after conversions. These factors include incomplete conversion, complexity of waste, separation process, sorting, etc. Additionally, these factors can be influenced by considering different strategies and techniques such as waste pre-processing, optimization of the conversion process, integration of multiple processes, and post-treatment stabilization and characterization. When considering the concept of integrated fermentation-MFC system, fermentation residues or effluents can be utilized in MFCs for conversion into multiple forms of bioenergy. This discussion has been updated in the revised manuscript (sections 3.2 and 3.3).

1. In different pages % numbers are given (for example in Lines 130-131): Do the values refer to wt% or volume %? In all the text such information may appear.

Thank you for the suggestion. The % number refers to weight % and it has been revised in Section 2.1. MSW Sources and Composition in the revised manuscript

2. Line 177: the starting material is labelled MSWC in the Figure (Is C used for Composition?). Why rubber has been considered as non-combustible?

We thank you for the comments. The figures have been already revised as per comments from the editor’s and reviewer’s comments. For clarification, MSWC stands for Municipal Solid waste composition. Rubber such as tires or rubber sheets is usually made up of solid rubber material and difficult to ignite and does not support combustion. These are made of long chains of polymers with the maximum percentage of nonflammable materials. These data have been cited from Ozcan, H. K., Guvenc, S. Y., Guvenc, L., & Demir, G. (2016). Municipal Solid Waste Characterization According to Different Income Levels: A Case Study. Sustainability, 8(10), 1044. https://doi.org/10.3390/su8101044. This citation has been included in the revised manuscript.

3. Line 204: define what is “XOS”

We thank the reviewer for the suggestion. XOS is the acronym for Xylooligosaccharides. Correction has been made in the revised manuscript.

4. Line 274: “heart valves”: quite specific – needs explanation.

Thank you for this comment. Heart valves are the form of useful products made from animal tissues, especially from swine, cow, and horse tissue. These are known as Xenografts. These have been mentioned in the manuscript because livestock waste is considered an effective waste valorization for the fabrication of heart valves.  This is cited from Tarafdar, A., Gaur, V. K., Rawat, N., Wankhade, P. R., Gaur, G. K., Awasthi, M. K., Sagar, N. A., & Sirohi, R. (2020). Advances in biomaterial production from animal derived waste. Bioengineered, 12(1), 8247-8258. https://doi.org/10.1080/21655979.2021.1982321. This citation has been included in the revised manuscript.

 

5. Figures 4 and 5 were not introduced in the text

Thank you for the comment. Figures 4 and 5 are already introduced in the text and again highlighted in the revised manuscript.

6. In Table 1, Power Output is expressed in different units such as V, mW/m2 or mW/m3, W/m2. For true comparison, it seems useful to try to present all results with the same unit, or present equations allowing conversion.

We thank the reviewer for this comment. The units were retrieved from the original literature. Due to the different experimental settings, energy measurements, and limited information provided in the literature, It’s difficult to unify units. However, some units have been updated in the revised manuscript, such as mV to V, W/m² to mW/m^2, and W/m³ to mW/m³. The detailed discussions have been updated in the revised manuscript (Section 3.2). Also, the footnote for the energy output unit has been added to Table 1.   

7. Line 584: “of m/Wm2 » : to be corrected

We thank the reviewer for highlighting the correction. m/Wm2 has been corrected to mW/m² in the section of Feedstock used in MFC (3.2.2) in the revised manuscript.

8. Lines 599 - 601: “as KmnO4 » : maybe KMnO4?

Thank you for pointing out this correction. The correction has been made in the revised manuscript.

9. Lines 633-637: Can the authors speculate on the reasons inducing such differences?

Thank you for the comment. The reason behind the different energy outputs is the effect of substrate and different configuration setups. Additionally, microbial activity, internal resistance, pH, and temperature also affect the power output.  The detailed discussion has been updated in section 3.2.2. (Feedstock used in MFC) in the revised manuscript.

10. Line 678: “from waste material using through WTE pathways could be”: what does this mean?

We thank the reviewer for this comment. The author expresses that WTE pathways are promising approaches for waste reduction, energy generation, and emission reduction. The revised sentence and statement have been updated to lines 586-592 in the revised manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report

This work “The Consolidated Approach of Biorefineries Using Municipal Solid Waste and Agricultural Waste to Produce Biofuels” is submitted as a review paper. From the title I was expecting a different content and from the abstract I imagined a deep review of MFC.

Therefore,  Several elements have to be considered prior to publication.

The title does not reflect the content of the paper, because MFC, which is the core element of the review is not even mentioned.

Introduction is too lengthy and present irrelevant information such as waste classification which is abundant in literature and does not give any value here.  Besides, it is not clear if such classification is based on global or regional or even national data, since references are not coherent. For example, ref. 22 refers to Chinese data, while ref. 22 on international data. Authors are required to clarify and contextualize their study in respect to a local or global perspective, not a mix of the two.

Authors should focus on the review of MFC, therefore while Section 3.22 is the relevant information of this paper, the previous 3.1, 3.2 should be rearranged and, potentially, become the introduction.

Therefore abstract and title should reflect better the content of the paper.

L527. What does the statement “These help in” means?

Section 5 is important in my view, and could deserve to be expanded if possible with a case study.

Graphical abstract is of poor quality, Authors are asked to improve it.

Author Response

This work “The Consolidated Approach of Biorefineries Using Municipal Solid Waste and Agricultural Waste to Produce Biofuels” is submitted as a review paper. From the title I was expecting a different content and from the abstract I imagined a deep review of MFC.

Therefore, Several elements have to be considered prior to publication.

The title does not reflect the content of the paper, because MFC, which is the core element of the review is not even mentioned.

We appreciate this comment. This study is focused on the consolidated fermentation-MFC system to produce bioenergy from organic waste. The title and abstract have been revised in order to bring up total attention to a better image of the overall manuscript. The title of the manuscript has been updated to “Waste-to-Energy Pipeline through Consolidated Fermentation-Microbial Fuel Cell (MFC) System.”   Both processes, fermentation and MFC, are reviewed and discussed in the manuscript, focusing on the concept of integrated biorefinery used for waste management and bioenergy production. This integrated system would hold potential opportunities to secure sustainability across environmental and energy sectors. The detailed discussions have been updated in the revised manuscript.  

1. Introduction is too lengthy and present irrelevant information such as waste classification which is abundant in literature and does not give any value here. Besides, it is not clear if such classification is based on global or regional or even national data, since references are not coherent. For example, ref. 22 refers to Chinese data, while ref. 22 on international data. Authors are required to clarify and contextualize their study in respect to a local or global perspective, not a mix of the two.

We thank the reviewer for this comment. The introduction has been revised according to reviewer’s comments. For the waste classification, the data has been confirmed regarding the global scenario. The data and references also have been updated in Section 2.1. ( MSW sources and composition) in the revised manuscript.

2. Authors should focus on the review of MFC, therefore while Section 3.22 is the relevant information of this paper, the previous 3.1, 3.2 should be rearranged and, potentially, become the introduction.

We appreciate this comment. Sections 3.1 and 3.2 have been reorganized and rewritten focusing on the fermentation and MFC technologies. The summary of biomass deconstruction technologies used in biorefineries has been merged into the Introduction in the revised manuscript.

3. Therefore abstract and title should reflect better the content of the paper

Thank you for the comment. The title and abstract have been updated. The title of the manuscript has been updated to “Waste-to-Energy Pipeline through Consolidated Fermentation-Microbial Fuel Cell (MFC) System.” Also, the abstract has been updated addressing the concept of the consolidated fermentation-MFC system.

4. What does the statement “These help in” means?

Thank you for pointing out this correction. The correction has been made in the revised manuscript.

5. Section 5 is important in my view, and could deserve to be expanded if possible with a case study.

We thank the reviewer for the suggestion. In the revised manuscript, the discussions about economic and environmental sustainability have been expanded in Section 4 (Waste-to-energy role in circular economy and environmental sustainability). The potential bioenergy production from the fermentation-MFC system using MSW and AR and its market value as well as the related environmental benefit were estimated according to literature data. Detailed discussions about the projected economic and environmental benefits have also been added in the revised manuscript. 

6. Graphical abstract is of poor quality, Authors are asked to improve it.

We thank the reviewer for the comment. The graphical abstract has been improved with the utmost perfect concept of the review article. The revised graphical abstract is added to the revised manuscript. 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

I thank Authors to have followed my comments and provided adequate answers and modifications. I find this revised version much improved and focused on the topic. Also title and abstract reflect better the content of the paper now.