Bio-Power Generation in Microbial Fuel Cell with Vermicompost Using Eisenia foetida

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper is in an overall well presented state indicating the proper methodology procedure and well established explanations in terms of charactetisations in soil MFCs.

Although some minor changes are  suggested to further accept:

Abstract Section

-Please add to the abstract the main reason for using Eisenia foetida specimens. Please avoid present tense and refer in passive voice

e.g. we used a substrate of black soil, tree bark, leaves, eggshells, and ground tomatoes should be written as:

"A substrate of black soil, tree bark, leaves, eggshells, and ground tomatoes was used"

Introduction section

-Elaborate more on the benefits of Vermicomposting adding more literature

- Please add a small paragraph indicating the reasons for choosing metallic electrodes for the MFCs.

The materials Section is properly presented

Results Section

-It would be proper to change the symbols in Figures 2,3,4,5 denoting the weeks. It is suggested to change to week 1, week 2 etc and not W1, W2, W3, W4. Please Change also in Table 4. Tables 1,2

-In line 203 is there a typo? Do you mean Figure 2 and Table 2?

Comments on the Quality of English Language

Minor editing of English language required.

Passive voice is suggested

Author Response

Authors appreciate the corrections and hope that the answers enlisted below in this document fulfill the expectations. We considered every suggestion as a valuable opportunity to improve and enrich enormously our work. Therefore, we have intended to be as punctual as we could to attend the decision of Major Revisions. Reviewer observations are highlighted using bold black font, our replies using blue font and changes in existing sentences have been written in italic font.

Abstract Section

1 -Please add to the abstract the main reason for using Eisenia foetida specimens.

We appreciate your comments to enrich the scientific content of our work. In the abstract we add line 2:

This research emphasizes the effect of using Eisenia foetida in vermicompost for power generation in microbial fuel cells (MFC), by accelerating the organic decomposition, the bioenergy generation is improved.

2.- Please avoid present tense and refer in passive voice

Abstract:

This research emphasizes the effect of using Eisenia foetida in vermicompost for power generation in microbial fuel cells (MFC), by accelerating the organic decomposition, the bioenergy generation is improved. A vermicompost-microbial fuel cell uses electrogenic microorganisms to convert chemical energy into electrical energy. In this work,  substrate of black soil, tree bark, leaves, eggshells, and ground tomatoes was used. The vermicompost MFC has a copper cathode and a stainless-steel anode. In this study the performance of MFC using different numbers of Eisenia foetida specimens is shown, with three specimens (MFC_W3), five specimens (MFC_W5), and seven specimens (MFC_W7). Our  key findings are showing, that by increasing the number of Eisenia foetida specimens do not brings a higher power densities as a result,  the best power density was observed, in the MFC_W3 and the MFC_W5 at the end of the fourth week, both presenting a total of 5 Eisenia foetida specimens with a power density of 192 mW m⁻². Therefore, optimal results were found when 330 g of substrate and 5 Eisenia foetida specimens were used, to achieve a maximum current density of 900 mW m⁻² and a maximum power density of 192 mWm⁻². This type of microbial fuel cell can be considered as an alternative for power generation with a significantly reduced environmental impact, considering the use of organic waste. It can be considered a game-changer in waste management and bioenergy projects.

 

Introduction section

3.- Elaborate more on the benefits of Vermicomposting adding more literature

1. Introduction

Line 35

Vermicomposting is a non-thermophilic, bio-oxidative process where worms and associated microbes transform matter [7 ]. According to the description of the vermicomposting process, it is possible to infer that bioenergy could be obtained simultaneously by using microbial fuel cells [8].

Line 39

The benefits of using vermicompost can be covered in: Bioprocesses as a sustainable alternative for the management of poultry waste, not only in terms of nutrient recycling but also by providing a clean source of energy [9], composting has been promoted as an important alternative for the treatment of organic waste [10], the use of vermicomposting reduces methane emissions compared to natural composting [11], the use of fertilizers derived from vermicompost, which is created from organic waste of animal or plant origin, has been proven to be an extremely effective method of enhancing soil quality. [12], promoting sustainable development, composting is an important alternative [10], composting represents an effective and environmentally friendly method of recycling organic waste, whereby it is converted into stable and mature fertilisers. [10], finally, the nutritional content can be improved by combining thermophilic biodegradation in rotating drum containers and vermicomposting based on Eisenia foetida [13].

4.-  Please add a small paragraph indicating the reasons for choosing metallic electrodes for the MFCs.

2.2. MFC Assemble

Line 122

The research is based on the quantification of the effect of the number of Eisenia foetida species and its relationship with the electrical power density, for which a stainless steel electrode is chosen for the anode due to its low corrosion in atmospheres containing oxygen, and copper as the cathode for its electrical conductivity.

Results Section

5.- It would be proper to change the symbols in Figures 2,3,4,5 denoting the weeks. It is suggested to change to week 1, week 2 etc and not W1, W2, W3, W4. Please Change also in Table 4. Tables 1,2

We appreciate your suggestions, and we have changed figures and tables.

6.- In line 203 is there a typo? Do you mean Figure 2 and Table 2

We appreciate your suggestions, and we have changed figures and tables.

Line 214

from 8 to 192 mW m⁻² (Figure 2 and Table 1). This behavior could be due to Eisenia

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors, 

In order to improve the rigor of the article, it is recommended that a specific discussion of the uncertainty associated with the instruments and measurement methods used be included. The latter would allow for the calculation of confidence intervals for the results. Without this information, conclusions about the efficiency and performance of MFCs should be interpreted with caution, as uncertainty could influence the reported values.

Figures 2, 3, 4, and 5 present the polarization and density curves for the cells over 4 weeks. However, to better understand the variability of the data, it is suggested that error bars be included.

On the other hand, Figure 6 shows the lighting of an LED using a series arrangement of MFCW3 cells. A schematic diagram of the connection could be included to optimize this figure and provide greater clarity.

In Tables 1 and 2, where the evolution of open circuit voltage, current density, and power density is shown over four weeks, it would be useful to include the standard deviation, which would help determine the significance of the differences between the cells.

Table 4 also presents the pH values ​​for each week, but the errors associated with the measurements are not mentioned.

Finally, it is recommended that the conclusions be supported by a more solid statistical analysis. In addition, future explorations, such as the use of different substrates, could be suggested. 

The article may be considered for publication, subject to consideration of the above comments.

Author Response

Authors appreciate the corrections and hope that the answers enlisted below in this document fulfill the expectations. We considered every suggestion as a valuable opportunity to improve and enrich enormously our work. Therefore, we have intended to be as punctual as we could to attend the decision of Major Revisions. Reviewer observations are highlighted using bold black font, our replies using blue font and changes in existing sentences have been written in italic font.

1.- Figures 2, 3, 4, and 5 present the polarization and density curves for the cells over 4 weeks. However, to better understand the variability of the data, it is suggested that error bars be included.

2. Materials and Methods

Lines to 143 to 146

The statistical behavior of the microbial cells was constructed; with the experimental results of the current density during the four weeks, the average was calculated, then two deviations were added to this average, one to the right and one to the left for the average point.

3. Results

Lines to 227 to 245

In the Microbial fuel cell control (MFCCT) shown in Figure 6a, the central line formed by green triangles corresponds to the average current density during the four weeks. At average current densities of 1.6 mA/m² it shows a standard deviation of 0.19, however at average current densities of 224 mA/m², the standard deviation is 191, meaning that the maximum contributions are made in the concentration region, which is related to the diffusion of the species. In the Microbial fuel cell (MFCw3) shown in Figure 6b, the standard deviation is 19 for average current densities of 11 mA/m². For average current densities of 488 mA/m2 the standard deviation is 335, presenting high values of standard deviation in the activation and concentration regions, as a function of time during the four weeks this microbial fuel cell is the one that increased its power density the most. In the Microbial fuel cell (MFCw5) shown in Figure 6c, the minimum standard deviation of 0.98, obtained in the activation region, for average current density values of 1.1 mA/m², the maximum standard deviation of 105 when 617 mA/m² is obtained, it is important to note how in the ohmic region there is a decrease in the standard deviation, understanding that a better conductivity is presented in the microbial cell. In the Microbial fuel cell (MFC_w7) shown in Figure 6d, presents the minimum standard deviation variations compared to MFC_CT, MFC_W3, MFC_W5, the minimum standard deviation value 0.65, is obtained at 0.005 mA/m², and the maximum standard deviation variation of 52 is related to the average current density of 229 mA/m².

FIGURE 6. Statistical behavior during the 4 weeks of experimentation. a) Control microbial fuel cell (MFC_CT), b) Microbial fuel cells with three Eisenia foetida specimens (MFC_W3), c) Microbial fuel cells with five Eisenia foetida specimens (MFC_W5), and d) Microbial fuel cells with seven Eisenia foetida specimens (MFC_W7).

4. Conclusions

Lines 352 to 355

In the present investigation, when there are high standard deviation variations (MFCCT), and the lowest power density values ​​are related to Figure 5a and Figure 6a. Conversely, when the standard deviations are minimal, the highest power densities are observed in the ohmic region (Figure 5c and Figure 6c), this hypothesis is proposed for future research.

2.- On the other hand, Figure 6 shows the lighting of an LED using a series arrangement of MFCW3 cells. A schematic diagram of the connection could be included to optimize this figure and provide greater clarity.

Thank you for the recommendation; the diagram has been included

Figura 6. Operation of the microbial fuel cell: a) MFC- stack energy test, b) Schematic Diagram of the MFC- stack.

3.- In Tables 1 and 2, where the evolution of open circuit voltage, current density, and power density is shown over four weeks, it would be useful to include the standard deviation, which would help determine the significance of the differences between the cells.

Lines 206 to 210

In Table 1 and Table 2, show that the minimum values ​​of standard deviation (σ) correspond to the open circuit potentials (OCV_MAX), with an average variation of 0.059 ± 0.4. However, the variation in standard deviation related to current densities, presents values ranging ​​from 36 to 367, thus, the main challenges are focused on this variable, which is related to the quantity of electrogenic bacteria, and the conductivity in the microbial cell.

 4.- Table 4 also presents the pH values ​​for each week, but the errors associated with the measurements are not mentioned.

Dear, thank you for your suggestion. When the pH measurement was carried out, the value remained constant for each experiment; that is, during the day the reading was taken, it did not vary.

 

5.- Finally, it is recommended that the conclusions be supported by a more solid statistical analysis. In addition, future explorations, such as the use of different substrates, could be suggested.

Thank you for your recommendation. Statistics is indeed a relevant factor. A hypothesis has been proposed in the conclusions, which, thanks to you, would be part of the following investigation.

4. Conclusions

Lines 352 to 355

In the present investigation, when there are high standard deviation variations (MFCCT), and the lowest power density values ​​are related to Figure 5a and Figure 6a. Conversely, when the standard deviations are minimal, the highest power densities are observed in the ohmic region (Figure 5c and Figure 6c), this hypothesis is proposed for future research.

 

 

 

 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript now meets the publication standards, and I recommend its acceptance.