Impact of Dragon Fruit Waste in Microbial Fuel Cells to Generate Friendly Electric Energy

Round 1

Reviewer 1 Report

This manuscript assembled a microbial fuel cells using red dragon fruit waste to produce electric energy. This project was interesting and there are several points that may help improve the manuscript.

1). What’s the main component of the red dragon fruit waste?

2) why were the zinc and copper electrodes preferred for assembling the fuel cell? It seems that the galvanic reaction may be another major source for generating the electric energy. If not, is it possible to use different electrodes?

3) What’s the product and molecular identification from the cathode? In another word, what’s the possible reactions happened on both side?

4) Are there any changes for both electrodes after long time cycling?

5) How about other fruit wastes for microbial fuel cells? What about their current research progress?

Author Response

Dear colleague, very grateful for the comments made to our investigation, I send the responses to each comment made.

1). What’s the main component of the red dragon fruit waste?

Ans. The network 20 has been placed regarding this, but it was not carried out experimentally, because it is already found in the literature.

2) why were the zinc and copper electrodes preferred for assembling the fuel cell? It seems that the galvanic reaction may be another major source for generating the electric energy. If not, is it possible to use different electrodes?

Ans. These selected electrodes were used because in previous works by our group of researchers high values of current and voltage were found due to their metallic nature, possibly a galvanic reaction may be present; reason for which an investigation with several fruits is carried out to observe this phenomenon. Graphite and carbon electrodes have also been used, but these did not give high current and voltage values, which is why zinc and copper electrodes were chosen.

3) What’s the product and molecular identification from the cathode? In another word, what’s the possible reactions happened on both side?

ANS.The anodic electrode was chosen because it is the electron acceptor for the generation of electrical energy, but the authors agree that we failed to characterize the microorganisms in the cathodic electrode, but when using Zinc, corrosion is observed in the state electrode end; for this reason it was not carried out. His point of view will be found for a future work.

4) Are there any changes for both electrodes after long time cycling?

Ans. A biofilm was observed on the anode electrode, but quite pronounced corrosion was observed on the cathode electrode, impairing the identification of microorganism molecules on that electrode.

5) How about other fruit wastes for microbial fuel cells? What about their current research progress?

Ans. Our group of researchers has been working with other types of vegetables and fruits, in which biocatalysts are being investigated to enhance the generation of electrical energy.

kind regards

Author Response File: Author Response.pdf

Reviewer 2 Report

Generalities

The manuscript entitled “Impact of Dragon Fruit Waste in Microbial fuel cells to generate friendly electric energy” aims to use fruit waste as energy source to generate electricity in microbial fuel cells. The treatment of solid wastes by using MFCs is interesting, but the article is not suitable for publication at the current stage.

Specifications

1)      Please check and reduce the number of decimals presented along the whole document (e.g., Line 96: 3.71667 ± 0.05304 mA; Line 187: 0.2478 ± 0.0234V).

2)      Introduction: Literature review of the usage of solid wastes is missing.

3)      Figure 2, 3: Please start the axis at 0 days, 0 mA.

4)      Results and discussion: When comparing current production data, please normalize to the anode electrode surface area.

5)      pH: Oxidation reactions occurring at the anode are expected to generate protons and thus, an acidification would be expected. Why is pH increasing?

6)      Conductivity: Pleas provide an explanation to the decrease of conductivity. Did the authors observe salt precipitation on the cathode electrode?

7)      Internal resistance. The authors should also consider that the H-type cell is a good design for proof-of-concept test, but it is highly inefficient from an electrochemistry perspective (e.g., high anode-cathode distance).

8)      An abiotic test is missing.

9)      It is not clear the advantage of using an MFC instead of anaerobic digestion, for example.

Comments for author File: Comments.pdf

Author Response

Dear colleague, very grateful for the comments made to our investigation, I send the responses to each comment made.

1)      Please check and reduce the number of decimals presented along the whole document (e.g., Line 96: 3.71667 ± 0.05304 mA; Line 187: 0.2478 ± 0.0234V).

Ans. The indicated corrections were made, standardizing everything with 2 decimal places.

2)      Introduction: Literature review of the usage of solid wastes is missing.

Ans. Added a paragraph on the importance of using solid waste

3)      Figure 2, 3: Please start the axis at 0 days, 0 mA.

Ans. done

4)      Results and discussion: When comparing current production data, please normalize to the anode electrode surface area.

Ans. Ok, all values were placed in cm2

5)      pH: Oxidation reactions occurring at the anode are expected to generate protons and thus, an acidification would be expected. Why is pH increasing?

Ans. Because in the anode the reduction of oxygen takes place, which when reacting with the protons (H+) forms water. When the reactions between protons, electrons, and oxygen at the cathode equals the production of protons, no change in pH occurs. (Lopez, 2014).
Lopez, J. (2014). Development of a microbial fuel cell (MCC) for application in wastewater treatment. Center for Research and Technological Development in Electrochemistry (CIDETEQ): https://cideteq.repositorioinstitucional.mx/jspui/bitstream/1021/144/1/Desarrollo%20de%20una%20celda%20de%20combustible%20microbiana%20%28CCM% 29%20for%20the%20application%C3%B3n%20in%20the%20treatment%20of%20wastewater%20%20%28Protected%29..pdf

6)      Conductivity: Pleas provide an explanation to the decrease of conductivity. Did the authors observe salt precipitation on the cathode electrode?

Ans. the precipitation was observed in the anodic chamber, due to the type of MFC used, which is a single chamber. Where one of the main effects of this phenomenon is attached to the decrease in conductivity values.

7)      Internal resistance. The authors should also consider that the H-type cell is a good design for proof-of-concept test, but it is highly inefficient from an electrochemistry perspective (e.g., high anode-cathode distance).

Ans. What you mention is exact, but the MFCs have also had good results and this design was used to reduce manufacturing costs. But it will be taken into account for a subsequent investigation.

8)      An abiotic test is missing.

Ans. This test is not considered for this investigation, so that the MFCs have the most natural conditions possible, but this will be investigated in a future work.

9)      It is not clear the advantage of using an MFC instead of anaerobic digestion, for example.

Ans. MFCs offer several operational and functional advantages over the technologies currently used to generate energy from organic matter, among which we can mention: They provide high efficiency in the direct conversion of energy from the substrate into electricity; They work efficiently at room temperature and even at low temperatures; They do not require gas treatment, in this case, the exhaust gases are enriched in carbon dioxide; They do not need energy input for aeration; They have the potential for widespread application in places lacking electrical infrastructure and also to broaden the diversity of fuels available to meet energy needs [1, 2]. In this way, they contribute to solving both the energy crisis and environmental pollution [3]. One of its most useful and immediate applications is the treatment of wastewater, for the production of renewable energy.
1. Rabaey, K.; Verstraete, W. Microbial Fuel Cells: Novel Biotechnology for Energy Generation. Trends Biotechnology. 2005, 23, 291–298, doi:10.1016/j.tibtech.2005.04.008.
2. Mora Collazos, A.; Bravo Montaño, E. Bacterial Diversity Associated with Anodic Biofilms in Microbial Fuel Cells Fed with Wastewater. Biolo Act. Columbia 2017, 22, 77, doi:10.15446/abc.v22n1.55766.
3. Hoang, A.T.; Nižetić, S.; Ng, K.H.; Papadopoulos, A.M.; Le, A.T.; Kumar, S.; Hadiyanto, H.; Pham, V.V. Microbial Fuel Cells for Bioelectricity Production from Waste as Sustainable Prospect of Future Energy Sector. Chemosphere 2022, 287, 132285, doi:10.1016/j.chemosphere.2021.132285.
kind regards

Author Response File: Author Response.pdf

Reviewer 3 Report

Impact of Dragon Fruit Waste in Microbial fuel cells to generate friendly electric energy. This article utilizes the organic waste to generate electricity in ecofriendly way. Some of the results are interesting, however following revisions can be made before publications:

1.       Manuscript writing is very poor. The abstract should be revised. The result should be connected to the approach of this work.

2.       How about the conductivity at different temperatures.

3.       In introduction section, the importance of biowaste can be explained with following articles:

Chemosphere, Volume 309, Part 1, December 2022, 136638, Chemical Engineering Journal, Volume 417, 1 August 2021, 129312

4.     Some grammatical errors should be rearranged. Some sentences are not properly arranged. 

Author Response

Dear colleague, very grateful for the comments made to our investigation, I send the responses to each comment made.

1. Manuscript writing is very poor. The abstract should be revised. The result should be connected to the approach of this work.

Ans. The summary, we find well organized. Some details are added please check if it's ok or let us know to improve it further.

2. How about the conductivity at different temperatures.

Ans. This test has not been carried out, however, there could be variations in conductivity, since temperature is an important variable in the process of electrical energy production, since this parameter can generate optimal conditions for bacterial growth, ensuring an increase in energy. electricity (Bermúdez and Bernal, 2018).

Bermúdez, M., & Bernal, E. (2018). Implementación de una celda de combustible microbiana a escala laboratorio para generación de energía eléctrica. World Development, 1(1), 1–15.DOI: https://doi.org/10.1016/j.worlddev.2018.08.012.

3. In introduction section, the importance of biowaste can be explained with following articles:

Chemosphere, Volume 309, Part 1, December 2022, 136638, Chemical Engineering Journal, Volume 417, 1 August 2021, 129312

Ans. Revised recommended information, and added requested information

4. Some grammatical errors should be rearranged. Some sentences are not properly arranged. 

Ans. Corrected the writing in English.
kind regards

Author Response File: Author Response.pdf

Reviewer 4 Report

          Impact of Dragon Fruit Waste in Microbial Fuel Cells to Generate Friendly Electric Energy

 Rojas-Flores Segundo, Santiago M. Benites, De La Cruz-Noriega Magaly, Juan Vives-Garnique, Nélida Milly Otiniano, Walter Rojas-Villacorta, Moisés Gallozzo-Cardenas, Daniel Delfín-Narciso  and Félix Díaz

This research is a very innovative and encompasses many tasks according to bioelectrochemistry, industrial biotechnology, environmental biotechnology. This manuscript showed possibility to generate electricity in an eco-friendly way using red dragon fruit (pitahaya) waste as fuel in single-chamber microbial  fuel on a laboratory scale using zinc and copper electrodes. Also, the yeast-like fungus Geotrichum candidum was identified by molecular biology methods.

Some comments to the authors:

1)     To correct the title of manuscript: „Impact of Dragon Fruit Waste in Microbial Fuel Cells to Generate Friendly Electric Energy“ i.e. to change some words the first lowercase letters into uppercase;

2)     It should be written at a current density of 5.06 A/cm² in 27 paragraph;

3)     It should be written correctly „countries [3-5]“ in 41 paragraph.

4)     It should be written correctly “at the same time [7]“ in 53 paragraph.

5)      It should be written correctly„which must be economical, have good conductivity and not be toxic to 309 microorganisms electrogenic“ in 310 paragraph.

6)     To check the list of references and it should be written names of bacteria, yeasts and plants in italic.

7)      It should be written names of bacteria in italic in the reference of 8 list: „Efficient Conversion of Agroindustrial Waste into D(-) Lactic Acid by Lactobacillus Delbrueckii Using Fed-Batch Fermentation“.

8)     It should be written names of plants in italic in the reference of 19 list: „Shade Improves Growth, Photosynthetic Performance, Production and Postharvest Quality in Red Pitahaya (Hylocereus Costaricensis)“.

9)     It should be written names of bacteria in italic in the reference of 28 list: „Identification of Emerging Industrial Biotechnology Chassis Vibrio Natriegens as a Novel High Salt-Tolerant and Feedstock Flexibility Electroactive Microorganism for Microbial Fuel Cell“.

10) It should be written names of plants in italic in the reference of 64 list: „Water-in-Oil-in-Water Nanoemulsions Containing Temulawak (Curcuma Xanthorriza Roxb) and Red Dragon Fruit (Hylocereus Polyrhizus) Extracts“.

11) It should be written names of bacteria in italic in the reference of 30 list: „Acidophilic Microorganisms Leptospirillum Sp., Acidithiobacillus Sp., Ferroplasma Sp. As a Cathodic Bioagents in a MFC“.

12) It should be written names of bacteria in italic in the reference of 33 list: „The Parallel Electron Transfer Pathways of Biofilm and Self-Secreted Electron Shuttles in Gram-Positive Strain Rhodococcus Pyridinivorans HR-1 Inoculated Microbial Fuel Cell“.

13) It should be written names of the filamentous yeast-like fungus in italics in the reference of 66 list: „Uncovering the Biotechnological Importance of Geotrichum Candidum“.

14) It should be written names of the filamentous yeast-like fungus in italics in the reference of 68 list: „Characterization of Cellulase from Geotrichum Candidum Strain Gad1 Approaching Bioethanol Production“.

15) It should be written names of plants in italic in the reference of 70 list: „Comparative Study of Betacyanin Profile and Antimicrobial Activity of Red Pitahaya (Hylocereus Polyrhizus) and Red Spinach (Amaranthus Dubius)“.

16) It should be written names of plants in italic in the reference of 71 list: „In Vivo and In-Vitro Evaluation of Antimicrobial Activity of Peel Extracts of Red Dragon Fruit (Hylocereus Polyrhizus)“.

17) It should be written names of yeast in italic in the reference of 72 list: „Preliminary Investigation of Electricity Production Using Dual Chamber Microbial Fuel Cell (DCMFC) with Saccharomyces Cerevisiae as Biocatalyst and Methylene Blue as an Electron Mediator“.

18) It should be written names of yeast in italic in the reference of 76 list: „Direct Electrochemical Determination of Candida Albicans Activity“.

Comments for author File: Comments.pdf

Author Response

Dear colleague, very grateful for the comments made to our investigation, I send the responses to each comment made.

1)     To correct the title of manuscript: „Impact of Dragon Fruit Waste in Microbial Fuel Cells to Generate Friendly Electric Energy“ i.e. to change some words the first lowercase letters into uppercase.

Ans ::Changed the first lowercase letters to uppercase.

2)     It should be written at a current density of 5.06 A/cm² in 27 paragraph;

Ans. it was corrected

3)     It should be written correctly „countries [3-5]“ in 41 paragraph.

Ans. it was corrected

4)     It should be written correctly “at the same time [7]“ in 53 paragraph.

Ans. it was corrected

5)      It should be written correctly„which must be economical, have good conductivity and not be toxic to 309 microorganisms electrogenic“ in 310 paragraph.

Ans. it was corrected

6)     To check the list of references and it should be written names of bacteria, yeasts and plants in italic.

Ans. it was corrected

7)      It should be written names of bacteria in italic in the reference of 8 list: „Efficient Conversion of Agroindustrial Waste into D(-) Lactic Acid by Lactobacillus Delbrueckii Using Fed-Batch Fermentation“.

Ans. it was corrected

8)     It should be written names of plants in italic in the reference of 19 list: „Shade Improves Growth, Photosynthetic Performance, Production and Postharvest Quality in Red Pitahaya (Hylocereus Costaricensis)“.

Ans. it was corrected

9)     It should be written names of bacteria in italic in the reference of 28 list: „Identification of Emerging Industrial Biotechnology Chassis Vibrio Natriegens as a Novel High Salt-Tolerant and Feedstock Flexibility Electroactive Microorganism for Microbial Fuel Cell“.

Ans. it was corrected

10) It should be written names of plants in italic in the reference of 64 list: „Water-in-Oil-in-Water Nanoemulsions Containing Temulawak (Curcuma Xanthorriza Roxb) and Red Dragon Fruit (Hylocereus Polyrhizus) Extracts“.

Ans. it was corrected

11) It should be written names of bacteria in italic in the reference of 30 list: „Acidophilic Microorganisms Leptospirillum Sp., Acidithiobacillus Sp., Ferroplasma Sp. As a Cathodic Bioagents in a MFC“.

Ans. it was corrected

12) It should be written names of bacteria in italic in the reference of 33 list: „The Parallel Electron Transfer Pathways of Biofilm and Self-Secreted Electron Shuttles in Gram-Positive Strain Rhodococcus Pyridinivorans HR-1 Inoculated Microbial Fuel Cell“.

Ans. it was corrected

13) It should be written names of the filamentous yeast-like fungus in italics in the reference of 66 list: „Uncovering the Biotechnological Importance of Geotrichum Candidum“.

Ans. it was corrected

14) It should be written names of the filamentous yeast-like fungus in italics in the reference of 68 list: „Characterization of Cellulase from Geotrichum Candidum Strain Gad1 Approaching Bioethanol Production“.

Ans. it was corrected

15) It should be written names of plants in italic in the reference of 70 list: „Comparative Study of Betacyanin Profile and Antimicrobial Activity of Red Pitahaya (Hylocereus Polyrhizus) and Red Spinach (Amaranthus Dubius)“.

Ans. it was corrected

16) It should be written names of plants in italic in the reference of 71 list: „In Vivo and In-Vitro Evaluation of Antimicrobial Activity of Peel Extracts of Red Dragon Fruit (Hylocereus Polyrhizus)“.

Ans. it was corrected

17) It should be written names of yeast in italic in the reference of 72 list: „Preliminary Investigation of Electricity Production Using Dual Chamber Microbial Fuel Cell (DCMFC) with Saccharomyces Cerevisiae as Biocatalyst and Methylene Blue as an Electron Mediator“.

Ans. it was corrected

18) It should be written names of yeast in italic in the reference of 76 list: „Direct Electrochemical Determination of Candida Albicans Activity“.

Ans. it was corrected

kind regards

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The point-to-point response letter seems to be reasonable. However, if the manuscript could include these answers into the manuscript accordingly and explain/analyze more in details, that would be much better for others to repeat/cite this paper in the future. Otherwise, I can't see any difference between revised version with the last one. Thanks.

Author Response

Dear colleague, I hope you are in good health.
Of course it is now placed in the manuscript, I hope you are happy with the corrections.

1). What’s the main component of the red dragon fruit waste?

Ans. The ref 20-22 has been placed regarding this, but it was not carried out experimentally, because it is already found in the literature.

It was placed in the manuscript in lines 90 to 96.

2) why were the zinc and copper electrodes preferred for assembling the fuel cell? It seems that the galvanic reaction may be another major source for generating the electric energy. If not, is it possible to use different electrodes?

Ans. These selected electrodes were used because in previous works by our group of researchers high values of current and voltage were found due to their metallic nature, possibly a galvanic reaction may be present; reason for which an investigation with several fruits is carried out to observe this phenomenon. Graphite and carbon electrodes have also been used, but these did not give high current and voltage values, which is why zinc and copper electrodes were chosen.

It was placed in the manuscript in lines 218-223.

3) What’s the product and molecular identification from the cathode? In another word, what’s the possible reactions happened on both side?

ANS.The anodic electrode was chosen because it is the electron acceptor for the generation of electrical energy, but the authors agree that we failed to characterize the microorganisms in the cathodic electrode, but when using Zinc, corrosion is observed in the state electrode end; for this reason it was not carried out. His point of view will be found for a future work.

It was placed in the manuscript in lines 218-223.

4) Are there any changes for both electrodes after long time cycling?

Ans. A biofilm was observed on the anode electrode, but quite pronounced corrosion was observed on the cathode electrode, impairing the identification of microorganism molecules on that electrode.

It was placed in the manuscript in lines 295 to 297.

5) How about other fruit wastes for microbial fuel cells? What about their current research progress?

Ans. Our group of researchers has been working with other types of vegetables and fruits, in which biocatalysts are being investigated to enhance the generation of electrical energy.

It was placed in the manuscript in lines 334 to 337.

Author Response File: Author Response.pdf

Reviewer 2 Report

All questions were answered.

Author Response

Thank you very much dear colleague, I hope you have a nice day

Reviewer 3 Report

Accept

Author Response

Thank you very much dear colleague, I hope you have a nice day

Round 3

Reviewer 1 Report

Accept