Activated Carbon Mixed with Marine Sediment is Suitable as Bioanode Material for Spartina anglica Sediment/Plant Microbial Fuel Cell: Plant Growth, Electricity Generation, and Spatial Microbial Community Diversity
Round 1
Reviewer 1 Report
In this work, authors studied activated carbon with marine sediment as the bio-anode in a Plant-MFC. The characterization of this system is complete and well-organized. The comparison of this work to previously reported results is also discussed in the manuscript.
Here are a few points the authors may need to revise:
The author should emphasize the novelty of this work. Is it the first time AC was used in Plant-MFC? What did other researchers use in Plant-MFC? What are the advantages of AC in this system? About the electricity generation, what is the practical application of electricity from this system? It seems that the current of the electricity for this system is quite low. The author should give a brief explanation of the system and give more detailed information about the anode in 2.1 Experimental setup section.Author Response
Dear Reviewer 1,
First we would like to thank you for your contribution to improve the quality of our paper. Please find our responses to your comments below:
The author should emphasize the novelty of this work. Is it the first time AC was used in Plant-MFC?
This study is not the first using AC in the Plant-MFC; though combining it with marine sediment is new. We mentioned this in the last paragraph of the introduction as follows:
“Although many studies about the anode materials for a Plant-MFC have been conducted, to our best knowledge, there is no study yet using activated carbon (AC) in the Plant-MFCs while studying the effect of marine sediment. It is well known that the activated carbon is a suitable bioanode material for microbial fuel cells fed with acetate [43,44]...” (line 110-113)
What did other researchers use in Plant-MFC?
We included as much as known diverse electrode materials used in the Plant-MFC and mentioned them in the introduction (line 105-109) and Table 1 to compare.
Line 105-109: “Several anode materials have been used in the Plant-MFCs to produce electricity. Among them were graphite granule and tezontle (a volcanic slag) [37], graphite felt/mat [15,17,24,25,27,28], graphite granule/grain [20,38,39], carbon fiber [40], nano-catalyzed graphite disc, rolled steel mesh with graphite fiber [41], and stainless steel mesh with biochar [42]”
What are the advantages of AC in this system?
Compared to other used electrodes, AC offers the additional advantage of potential electricity storage and sediment remediation. Several characteristics of AC were mentioned throughout the manuscript. According to the study, AC shows a capability to support plant growth, especially when mixed with marine sediment. This capability provides a possibility to implement this system in a real environment together with AC amendment, especially in a tidal area. This implementation of AC can give extra functions compared to other electrode materials. This because AC is used for soil, water i.e. sediment remediation. Furthermore, the capacitive behaviour of AC (as described in 3.2) in the system may be utilised to store electric charges for later use. To highlight this advantage we reformulated the last sentence of the conclusions (line 556-558) as follows: “The advantage of AC over other electrode materials is the provision of additional functions like electricity storage or sediment remediation.”
About the electricity generation, what is the practical application of electricity from this system? It seems that the current of the electricity for this system is quite low.
Plant-MFCs are still small devices delivering power to sensors [77]. Scale-up is to be proven to generate more electricity that could open applications that require more electricity, In section 3.2 of our result and discussion (line 429-431), we have mentioned that the Plant-MFC could be coupled with a low power use sensor as show by another study.
The author should give a brief explanation of the system and give more detailed information about the anode in 2.1 Experimental setup section.
We decided not to include more detail information about the anode and the reactor description in this paper because it was extensively described in the previously published open access paper as referenced in line 137-138. This information is therefore readily available.
We hope that we have provided sufficient information regarding to your comment.
On behalf of the Authors
Reviewer 2 Report
The manuscript submitted by Sudirjo et al. demonstrates that marine sediments blended with activated carbon are potent bioanodes in wetland plant-microbial fuel cells (MFCs). These blends enhance electricity generation as well as maintain the growth of common wetland plants.
This study overall is comprehensive and complete. The experimental observations reasonably justify the conclusions. I only have a few comments for the authors to improve the clarity of their discussions.
Please state what the cathodes of the wetland MFCs are in the Experimental section. Line 305: It is unclear why the "adsorption capability" of activated carbon limit the nutrient supply. This statement also lacks experimental evidence. Please elaborate on this sentence and provide corresponding experimental result(s). Figure 6: It is better to add notes explaining what happened when the current reached zero and raised again. The authors have done an excellent job in explaining this issue in the text, but adding notes in the figure could help readers grasp the idea easily. Figure S8: What are the possible reasons for the potential fluctuation of devices C and H? Please explain in the main text. Figure and table numbers in the Supporting Information should be accompanied by a letter S. The acknowledgment is incomplete. Please briefly explain the microstructure of activated carbon in the Introduction section.Author Response
Dear Reviewer 2,
First we would like to thank you for your contribution to improve the quality of our paper. Please find our responses to your comments below:
Please state what the cathodes of the wetland MFCs are in the Experimental section.
The cathode information was added into the manuscript, see line 146-154:
“In the cathode compartment (22cmx22cmx1cm; with a winding channel for catholyte flow), graphite felt was used as an electrode. This graphite felt (22cmx22cm; 3mm thickness, Grade WDF, National specialty product carbon and Graphite Felt, Taiwan) was woven with a titanium wire as a current collector. From day 1-105, a nitrate-less, sulfate-less, ammonium-rich plant growth medium was utilised as catholyte. Then from day 105 until the end of the experiment, the plant growth medium catholyte was replaced with demi water. In both cases, the catholyte was aerated with ambient air using an aquarium pump and recisculated into the cathode chamber in a close cycle via a 1 liter bottle with a pump (Watson-Marlow 505S, Rotterdam, The Netherlands at 30 rpm). Total catholyte volume in the close cycle was maintained at 1L[45]. “
Line 305: It is unclear why the "adsorption capability" of activated carbon limit the nutrient supply. This statement also lacks experimental evidence. Please elaborate on this sentence and provide corresponding experimental result(s).
We added extra information about adsorption capability of the AC (see line 323-328).
"Other studies have proven that activated carbon are able to adsorb various compounds such as acetate, ammonium, phosphate, nitrate, sulphate, and metal ions [62–69]. In this study, the nutrient supply was mainly from plant growth medium and leftover acetate (SI Table S6) from previous experiment. Conductivity and pH remained in the same order of magnitude in both the anolyte and catholyte (SI Table S6). This suggests that still some salts/nutrients are available; though whether specific nutrients were becoming limiting could not be revealed"
The experimental data about acetate concentration, pH and conductivity was added in the SI Table S6
Figure 6: It is better to add notes explaining what happened when the current reached zero and raised again. The authors have done an excellent job in explaining this issue in the text, but adding notes in the figure could help readers grasp the idea easily.
An additional explanation was added into Figure 6 caption (line 404-405).
Figure S8: What are the possible reasons for the potential fluctuation of devices C and H? Please explain in the main text.
We explained it in the manuscript. See line 476-479:
“Some Plant-MFCs (MS100 and AC33) fluctuated on current and anode/cathode potential. Since this did not happen in both duplicates, it could not be attributed to the type of electrode materials used. Other parameters that may cause this phenomena need to be further investigated while several Plant-MFC reports show dynamic behaviour[32]”Figure and table numbers in the Supporting Information should be accompanied by a letter S. Agree. All Figures, Tables and Methods in the SI are accompanied by a letter S.
The acknowledgment is incomplete.
Acknowledgment was completed.
Please briefly explain the microstructure of activated carbon in the Introduction section.
We added the following text (see line 57-62 Introduction): The capability of AC adsorbs organic compounds is controlled either by physical interaction or by chemical interaction between AC surface area and absorbents. The adsorption rate is influenced by molecular size of the organic compounds and distribution of the AC pores [8,9]. The activated carbon materials have three types of pores: micropores(<2nm), mesopores(2-50nm), and macropores(>50nm). The surface area of AC is determined by the presence and distribution of these pores [10].
We hope that we have provided sufficient information regarding to your comments.
On behalf of the Authors
