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Article

Effect of Supporting Carbon Fiber Anode by Activated Coconut Carbon in the Microbial Fuel Cell Fed by Molasses Decoction from Yeast Production

by
Paweł P. Włodarczyk
* and
Barbara Włodarczyk
*
Institute of Environmental Engineering and Biotechnology, University of Opole, ul. Kominka 6a, 45-032 Opole, Poland
*
Authors to whom correspondence should be addressed.
Energies 2024, 17(15), 3607; https://doi.org/10.3390/en17153607
Submission received: 2 June 2024 / Revised: 18 July 2024 / Accepted: 19 July 2024 / Published: 23 July 2024
(This article belongs to the Section A4: Bio-Energy)
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Abstract

:
A microbial fuel cell (MFC) is a bioelectrochemical system that generates electrical energy using electroactive micro-organisms. These micro-organisms convert chemical energy found in substances like wastewater into electrical energy while simultaneously treating the wastewater. Thus, MFCs serve a dual purpose, generating energy and enhancing wastewater treatment processes. Due to the high construction costs of MFCs, there is an ongoing search for alternative solutions to improve their efficiency and reduce production costs. This study aimed to improvement of MFC operation and minimize MFC costs by using anode material derived from by-products. Therefore, the proton exchange membrane (PEM) was abandoned, and a stainless steel cathode and a carbon anode were used. To improve the cell’s efficiency, a carbon fiber anode supplemented with activated coconut carbon (ACCcfA) was utilized. Micro-organisms were provided with molasses decoction (a by-product of yeast production) to supply the necessary nutrients for optimal functioning. For comparison, an anode made solely of carbon fibers (CFA) and an anode composed of activated carbon grains without carbon fibers (ACCgA) were also tested. The results indicated that the ACCcfA system achieved the highest cell voltage, power density, and COD reduction efficiency (compared to the CFA and ACCgA electrodes). Additionally, the study demonstrated that incorporating activated coconut carbon significantly enhances the performance of the MFC when powered by a by-product of yeast production.

1. Introduction

Microbial fuel cells (MFCs) have received much attention recently as they allow the degradation of waste, such as wastewater, into electricity generation [1,2,3]. Moreover, during operation, MFCs enable wastewater pre-treatment, which, in turn, may help reduce the costs of wastewater treatment [4]. MFC is a bioelectrochemical system (BES) that uses micro-organisms to generate electricity [5,6,7]. The first report on the production of electrons by micro-organisms dates to the beginning of the 20th century. M.C. Potter, a Professor of Botany at the University of Durham, observed that during the decomposition of organic matter by micro-organisms, a flow of electrons is created [8]. But, intensive research on the application of this discovery in MFCs only began in the 1960s [9]. At that time, it was believed that the addition of expensive exogenous mediators was necessary for the efficient production of bioelectricity using MFCs. However, in 1999, Kim et al. constructed a cell in which energy was generated by a naturally occurring consortium of bacteria without the need for external mediators [10]. The results obtained then sparked in renewed interest in this topic, especially in light of the need for alternative sources of renewable energy. Consequently, in the early 2000s, there was significant development in research on MFCs technology [1,3,11,12,13,14,15,16].
In MFCs, the anode compartment contains a variety of inoculum including representatives of various species of micro-organisms. In addition to many unidentified micro-organisms, there are identified bacteria belonging to the classes Alphaproteobacteria, Bacteroidetes, Betaproteobacteria, Clostridia, Deferribacteres, Deltaproteobacteria, Flavobacteria, Gammaproteobacteria, Nitrospirales, Planctomycetes, Sphingobacteria, or Spirochaetes, as well as fungal cells, such as those from the genus Saccharomyces or Pichia [17,18,19,20]. However, it is bacteria that are mainly used in the currently researched MFCs [21]. The diversity of the microbial community within an MFC is determined not only by the origin of the inoculum sample, but also by the type of fuel used to power the MFC, the presence of redox mediators and oxygen conditions in the bioreactor [2,21]. In the case of fuels for MFCs, pure substances such as acetate, glucose, cysteine, and ethanol can be used, as well as mixtures of organic compounds, including wastewater, liquid animal waste, landfill leachate, and liquid agricultural and industrial waste [22,23,24].
Electrons produced by micro-organisms are transferred to the anode (in the anode chamber) through direct or indirect electron transfer [2,20,25]. Figure 1 shows the electron transfer to the electrode.
Only some genera and species of bacteria are electrochemically active through direct conduction mechanisms, such as Shewanella or Geobacter (Figure 1A) [26,27,28]. These bacteria can transfer electrons even within multilayers of cells via a dense network of appendages with metal-like conductivity called bacterial nanowires [29]. The transfer may occur cell by cell over distances of more than 10 mm, until electrons are donated to the electrodes (Figure 1B) [30]. In contrast, bacteria such as Pseudomonas or also Shewanella can transfer electrons through soluble mediators, both natural (e.g., sulfate reducing spices) and synthetic (e.g., methylene blue or neutral red) (Figure 1C) [29,30,31].
The electrons then pass through the external load to the cathode (in the cathode chamber), where they are reduced by an oxidant (mainly oxygen) [32,33]. In MFCs, micro-organisms act as a catalyst for the process [21]. Therefore, the rate of electron production is limited by their metabolism [34]. The functioning of micro-organisms depends on the consortium of micro-organisms, i.e., the biofilm formed on the anode [22,35,36,37,38,39,40].
During the development of the biofilm, one can observe various stages: the development of non-electroactive bacteria (non-EAB), the development of nonspecifically electroactive bacteria (nonspecific EAB), and the development of specifically electroactive bacteria (specific EAB). Both types of electroactive bacteria (nonspecific EAB and specific EAB) are adapted to extracellular electron transfer (EET). In the case of MFCs, the main focus is the development of EAB due to the provision of conditions that allow for electricity flow [41,42,43,44]. In the case of biofilm development on MFCs electrodes, two main stages of development of the bacterial community of anode biofilms can be distinguished. The first stage lasts about 4 days. During this time, all types of bacteria initially settle on the electrode. Then, EAB begin to predominate over non-EAB, until practically only EAB develop on the electrode (both specifically EAB and nonspecifically EAB). At this point, the second stage of biofilm development begins. This stage involves a constant increase in the proportion of specifically EAB (adapted to EET) in the biofilm. The biofilm formation stage for MFCs concludes when the number of specific EAB significantly outweighs the number of nonspecific EAB in the biofilm [45]. At this point, the electrode (with biofilm) can be considered ready for use in MFCs. Figure 2 shows the stages of biofilm formation on the electrode.
Therefore, in a BES such as an MFC, ensuring appropriate conditions for the development of micro-organisms is extremely important [37]. It is crucial to maintain the appropriate temperature, pH, and other environmental factors, as well as to provide a suitable surface for biofilm formation [38], which means using an appropriate anode [39]. The anode has a major impact on MFC performance because the materials and structure of the anode can influence microbial biofilm formation and, consequently, electron transfer efficiency. Such an anode must primarily fulfill several functions: biocompatibility, good electrical conductivity, and large surface area [22,39]. Additionally, one important feature should be the low cost of the electrode [5,6,7,25]. Most often, metals and carbon-based materials are used as electrode materials in MFCs [1,2,5,25,39,40]. The tested metallic materials include stainless steel, copper, nickel, silver, and titanium [40,46,47], as well as metal alloys such as Ni-Co, Cu-B, or Cu-Ag [48,49,50]. Metals and their alloys have high electrical conductivity and electrocatalytic activity but are not resistant to corrosion, especially in environments containing chloride ions. Additionally, metal ions released from metal anodes may reduce the efficiency of micro-organisms or be harmful to them [2,51]. These ions may also be potentially dangerous to the environment [38]. Therefore, other types of electrodes, such as composite [40] or carbon-based electrodes, are also used in MFCs. However, carbon-based materials are the most used. This is due to the high biocompatibility of carbon electrodes, which is crucial when selecting electrodes for MFCs. Carbon felt, carbon paper, carbon fiber, and similar materials are most often used as carbon-based electrodes [52,53,54,55,56,57,58,59,60]. These materials have good electrical conductivity and corrosion resistance, but have low catalytic activity, which limits the overall performance of MFCs. One solution to the limitations of carbon-based materials is the use of activated carbon (AC). AC has a highly porous structure, large surface area, and high electrocatalytic activity. Electrode made of AC can be used in MFCs as an alternative to a platinum (Pt) cathode [61,62,63]. AC can also be used to build an anode, although its conductivity is not very high. These types of applications of activated carbon as anodes are also being explored in MFCs research [64,65,66,67]. AC is a promising electrode material, mainly due to its biocompatibility, good conductivity, biodegradability, and low cost. Activated carbon has been used in many MFCs developments, with research utilizing AC from sources such as chestnut shells [67] or coconut shells [68].
One of the main barriers to the widespread use of MFCs is the small amount of bioelectricity obtained relative to the costs of building them, particularly the cost of electrodes and proton exchange membrane (PEM). Although activated carbon-based materials do not allow for a significant increase in the voltage and power of the cell, they are characterized by a much lower price, which is several to a dozen times lower than that of carbon materials specially prepared for electrode production [69,70]. Moreover, it is important to explore the possibility of omitting PEM, which, while significantly reducing the cell’s efficiency, also contributes to a several-fold reduction in MFC construction costs. Therefore, research is necessary to both increase the efficiency of bioelectricity production in MFCs and simultaneously reduce the costs of the necessary components [71,72].
In this work, the effect of using a biocompatible electrode (anode) made from activated carbon (derived from coconut shells) in a laboratory-scale microbial fuel cell fed by process wastewater was analyzed.

2. Materials and Methods

One of the assumptions of the study was to minimize component costs and, consequently, to minimize MFC costs. The main elements that increase the costs of MFC construction are the PEM and the materials for the electrodes. As a result, the PEM was omitted, and a steel cathode and low-cost anode material made mainly from by-products were used. It was also decided to use an anode with high biocompatibility, hence the choice of a carbon-based material. Therefore, the activated carbon derived from coconut shells was used as the anode material. Activated coconut carbon (ACC) in the form of grains was used for the research. ACC grains, intended mainly for distilling, were purchased as a finished product (Deptana, Łódź, Poland). According to the manufacturer’s information, the degree of ACC grains fragmentation was 0.6–2.3 mm (Figure 3). The active surface on which biofilm can develop is minimum of 1050 m2·g−1 (according to the manufacturer’s information). Before use, the ACC was etched with a 5% solution of hydrochloric acid to remove ash and dry impurities (Figure 3, 3). Next, the ACC was dried in the dryer (Figure 3, 5). Figure 3 shows the scheme of preparing the ACC for use as the anode in MFC.
To ensure the highest possible conductivity, the anode chamber was filled with 50% ACC, providing the grains with multiple contact points to enhance electrical conduction (a common issue with activated carbon electrodes). To further increase the conductivity and collect electrons from the ACC, a carbon fiber brush was also placed in the anode chamber. This system, referred to as CFA + ACC, represents an anode chamber with activated coconut carbon and a carbon fiber anode (ACCcfA) (Figure 4B).
As material for the cathode, steel springs (SSC) was applied (Figure 4C,D, Figure 5 and Figure 9). The springs used in the study were made of AISI 304 alloy, which contains at least 18% chromium, 8% nickel, and a maximum of 0.08% carbon. Before filling the cathode chamber, the springs were washed in sodium hydroxide solution and then rinsed thoroughly with water several times. To obtain high conductivity of the cathode, the steel springs were tightly wound around a steel wire made of the same material. Additionally, after placing the cathode in the cathode chamber, the chamber was filled by steel springs (Figure 4D).
Figure 4 shows (A) CFA, (B) anode chamber with ACCcfA, (C) SSC, and (D) cathode chamber with SCC (B).
To compare the performance of the anode constructed in this manner, an anode made solely of carbon fibers (CFA) and an anode using ACC grains without carbon fibers (ACCgA) were also utilized (Figure 5; 1,2,3). As a laboratory-scale MFC, a simple glass vessel (made of borosilicate glass) with chambers separated by separator made of sintered glass (G-4) was used (Figure 5; 7). During the operation of the microbial fuel cell (ML-MFC), the cathode chamber containing the steel springs cathode was constantly aerated (5 L·h−1) by stone air bubbler. The electrical circuit of the ML-MFC was constantly connected with a 100 Ω resistor (Figure 5; R). Figure 6 shows scheme and view of the laboratory-scale MFC employing ACCcfA used in research.
For feeding the MFC, the molasses decoction from yeast production (MDYP) was used. MDYP is a by-product of baker’s yeast production and is typically used as fertilizer. It is obtained by concentrating process yeast wastewater in the evaporation battery system (EBS). Due to the high temperature of wastewater evaporating in EBS, live yeast cells are eliminated, ensuring long-term storage necessary for using MDYP as a fertilizer [73]. MDYP is a thick liquid, so before using it in the MFC, it was mixed with water in a ratio of 1:5. The initial chemical oxygen demand (COD) concentration of the diluted MDYP was 1545–1575 mg·L−1. The acidity of the wastewater was 6.8 pH, and the conductivity of wastewater was 2.17 mS·cm−1. All measurements were performed at temperature of 25 °C. To maintain the set temperature during MFC operation, the MFC was immersed in a thermostat-powered water bath.
To obtain a fully functioning electrode for an MFC, it is necessary to perform several start-ups [74,75,76,77] that allow the development of a biofilm containing specifically electroactive bacteria (EAB) adapted to extracellular electron transfer (EET) (Figure 2) [45]. For this purpose, the electrode was inoculated with micro-organisms from a functioning MFC [60], which were previously collected from the activated sludge of a wastewater treatment plant. The MFC was then flooded with MDYP, and the electrical circuit was closed with external resistance. In addition to generating electricity, the flow of electrons primarily ensures the development of electricity-producing micro-organisms, which constituted the first start-up. After the nutrients were depleted (as determined by the drop in cell voltage), the used MDYP was replaced with fresh MDYP, and the circuit was closed again for another start-up. This procedure (start-up) was repeated until a stable cell voltage was achieved, meaning that after replacing the used MDYP with fresh MDYP, the voltage remained at a relatively stable level. At that point, it was considered that the electrode had developed a stable biofilm containing specifically EAB adapted to EET.
For mixing the ACC with solution of hydrochloric acid and for mixing MDYP with water, a TechnoKartell TK 22 magnetic stirrer (Kartell S.p.A.—LABWARE Division, Noviglio, Italy) was used. For drying the ACC, an ED 115 dryer (Binder GmbH, Tuttlingen, Germany) was used, and pH and conductivity measurements were performed using a HI 5522 (HANNA Instruments, Woonsocket, RI, USA). For measuring the MFC operation at a set temperature, a Medingen E5s-B12 thermostat (GK Sondermaschinenbau GmbH, Labortechnik Medingen, Arnsdorf, Germany) was used. Electrical measurements of the ML-MFC were conducted using a Fluke 8840A multimeter (Fluke Corporation, Everett, WA, USA) and a PGSTAT302N potentiostat (Metrohm-Autolab BV, Utrecht, The Netherlands). For temperature measurements, a UNI-T UT33C multimeter (UNI-Technology, Hongkong, China) was used. COD reduction measurements were performed using a Hanna HI 83224 wastewater treatment photometer (HANNA Instruments, Woonsocket, RI, USA).

3. Results and Discussion

In the first step, the cell voltage during the start-ups of the MFC was measured. Figure 6 shows the cell voltage obtained during three consecutive MFC start-ups. The MFC start-ups were conducted for three different electrode configurations (CFA/SSC; ACCgA/SSC; ACCcfA/SSC). The cell voltage values are referenced to the voltage of the cell without the participation of micro-organisms (MFC with electrodes filled with diluted molasses decoction).
It should be noted that during the first start-up, the MFC did not generate significant voltage for a long time, apart from a negligible voltage in the range of 5–11 mV. This condition persisted for 100–120 h, depending on the electrode system. The longest duration of no significant cell voltage (120 h) was recorded for the ACCgA/SSC electrode system. The duration (100 h) was observed for both the CFA/SSC and ACCcfA/SSC electrode systems. After this period, the cell voltage began to increase, although this increase was not significant, reaching only approximately 23–53 mV, depending on the electrode system. This condition corresponds to the first stage of biofilm formation on the anode in the MFC (Figure 2). Following the second start-up, the cell voltage increased to 51–116 mV, depending on the electrode system. However, this was still not a satisfactory cell voltage. Consequently, another MFC start-up was conducted. After the third start-up, the cell voltage increased significantly to 116–248 mV (depending on the electrode system). The highest value of cell voltage (248 mV) was obtained for the ACCcfA/SSC electrode system, while the CFA/SSC electrode system achieved a value of 229 mV. However, the ACCgA/SSC electrode system produced the lowest cell voltage, at 116 mV. After the third start-up, the cell voltage no longer increased during subsequent start-ups, indicating that the cell voltage had stabilized. Thus, the third start-up was considered successful. A successful start-up also signifies the full development of the biofilm on the anode.
It should be noted that the low cell voltage of ACCgA/SSC electrode system results mainly from the low conductivity of the carbon grains. Although biofilm forms on the grains, it does not consist solely of EAB adapted to EET. This is mainly due to the low conductivity of the ACC grains, which hinders the development of EAB adapted to EET. The composition of the biofilm, with its limited ability to produce electrons (as it does not predominantly consist of EAB adapted to EET), leads to reduced electrode performance. Consequently, this reduces both the cell voltage and the overall efficiency of the MFC. However, when using the ACCcfA/SSC electrode system, an increase in cell voltage was noticed compared to the CFA/SSC electrode system. This means that part of the voltage obtained (in ACCcfA/SSC electrode system) is generated by ACCg (with biofilm). So, using ACCg together with CFA (ACCcfA/SSC electrode system) can increase the cell voltage by 8.3%. However, it should also be noted that after the third start-up using the ACCcfA/SSC electrode system, there is a faster consumption of substrates in the anode chamber, indicated by a faster drop in cell voltage due to the increased biofilm on ACCcfA.
Next, the cell voltage of the MFCs with various electrode systems was measured both in a single cycle and over six cycles (continuous/cycling feeding of the MFC). Figure 7 shows the cell voltage of the MFCs fed by the MDYP in (A) one cycle and (B) six cycles.
Analysis of the cell voltage in one cycle after biofilm stabilization (Figure 7A) showed that for the ACCgA/SSC electrode system, the cell voltage was relatively low, reaching a maximum value of 63 mV. In contrast, the CFA/SSC electrode system exhibited a much higher cell voltage, with a maximum value of 251 mV. However, in the ACCcfA/SSC electrode system, the highest cell voltage was obtained, reaching a maximum value of 274 mV. The average increase in cell voltage during six consecutive cycles was 6%. It should be noted, however, that with the ACCcfA/SSC electrode system, the substrates for micro-organisms (MDYP) are consumed very quickly, resulting in a rapid drop in cell voltage after approximately 100–110 h of operation. This is mainly due to the increased surface area on which the biofilm resides, leading to a larger biofilm (CF + ACCg) that requires more material for nourishment. For this reason, when measuring a series of MFC feeding cycles (Figure 7B), a decision was made to feed the biofilm every 110 h.
Next, the power density achieved during MFC operation with different electrode systems (ACCgA/SSC, CFA/SSC, and ACCcfA/SSC) was examined. Additionally, the polarization curves were analyzed. Figure 8A shows power density curves, and Figure 8B shows the polarization curves obtained in the MFC (Figure 5) using ACCgA/SSC, CFA/SSC, and ACCcfA/SSC electrode systems.
Using the CFA/SSC electrode system, the power density reached a value of 23 mW·m−2. However, similar to the cell voltage, the power density reached its highest value (26 mW·m−2) for the ACCcfA/SSC electrode system, representing an increase of 13.0%. In contrast, the ACCgA/SSC electrode system obtained the lowest power density value of 5 mW·m−2. It should be noted that the power density was consistently higher for the ACCcfA/SSC electrode system across the entire range of current densities. The current density values for the ACCgA/SSC electrode system should only be considered as a reference, illustrating the impracticality of this solution mainly due to its very low conductivity. The results indicate that these values can potentially be increased by augmenting CFA with the addition of ACC. ACC is not an expensive material, is biocompatible, and is produced from a by-product.
Next, the COD reduction during one cycle of MFC operation was analyzed. Since the organic material (MDYP) was replaced after each cycle, the limit value of COD reduction effectiveness could not be determined. Therefore, the COD reduction was analyzed in each individual cycle. Measurements of COD concentration reduction was performed before flooding the MFC and after each complete single MFC operation cycle.
Figure 9 shows the COD reduction in a full single cycle until the cell voltage disappears (to the value when the cell voltage remained at a stable low value) and in six single cycles.
In one full cycle of MFC operation (until the cell voltage remained at a stable low value), COD reduction was achieved for all electrode configurations. In the case of one full cycle (Figure 9A), the highest COD reduction efficiency (33%) was achieved for the ACCcfA/SSC electrode system. For the CFA/SSC electrode system, a 26% COD reduction efficiency was obtained, whereas the ACCgA/SSC electrode system achieved a 18% efficiency. Therefore, the increase in COD reduction efficiency of the ACCcfA/SSC electrode system compared to the CFA/SSC electrode system is 27%. Due to the lower electrical conductivity, the biofilm formed on ACC grains includes not only EAB specifically adapted to EET (Figure 2), but also other micro-organisms that metabolize organic matter. The ACCcfA/SSC electrode system has a significantly larger surface area compared to the CFA/SSC electrode system, providing more space for biofilm development. This larger biofilm accelerates the reduction in organic matter, resulting in a faster decrease in COD concentration, albeit at the expense of generating less bioelectricity. Over six 110 h cycles, the average COD reduction values obtained are slightly lower (Table 1).
Table 1 lists the average cell voltage (analyzed during six feeding by the MDYP cycles), maximum power density values, and average COD reduction in six cycles, for the various electrode configurations (ACCgA/SSC, CFA/SSC, and ACCcfA/SSC).
As indicated by the data in Table 1, the average cell voltage of the ACCcfA/SSC electrode system was 23% higher compared to the CFA/SSC electrode system, and more than four times higher than the average cell voltage of the ACCgA/SSC electrode system. The highest power density (29 mW·m−2) was also attained with the ACCcfA/SSC electrode system, marking a 26% increase compared to the CFA/SSC electrode system. Additionally, the ACCcfA/SSC electrode system achieved the highest average COD reduction efficiency (36%) over six cycles, representing a 44% increase compared to the CFA/SSC electrode system.

4. Conclusions

The study investigated the impact of supporting CFA with activated ACC in a laboratory-scale MFC fed with MDYP. The operation of the MFC was compared across three electrode systems: ACCgA/SSC, CFA/SSC, and ACCcfA/SSC. The results demonstrated that incorporating ACCg influenced an increase in cell voltage, power density, and COD reduction efficiency. The ACCgA/SSC electrode system served as a reference for assessing the activity of ACCg as an anode. To evaluate the functioning of the ACCcfA/SSC electrode system (supporting a carbon fiber anode with activated coconut carbon), this system was compared with the CFA/SSC electrode system. It was shown that the use of the ACCcfA/SSC electrode system allows for a 6% increase in average cell voltage, a 13% increase in maximum power density, and a 27% increase in COD reduction efficiency compared to the CFA/SSC electrode system. Therefore, it has been demonstrated that the addition of ACC (produced from a by-product) improves the operation of an MFC fed with by-products from yeast production (MDYP).

Author Contributions

Conceptualization, P.P.W.; methodology, P.P.W.; investigation, P.P.W. and B.W.; data curation, P.P.W. and B.W.; writing—original draft preparation, P.P.W. and B.W.; writing—review and editing, P.P.W. and B.W.; visualization, P.P.W. and B.W.; supervision, P.P.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.

Acknowledgments

The research was conducted at the International Research and Development Center of the University of Opole for Agriculture and the Agri-Food Industry (MCBR UO, Opole, Poland).

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Electron transfer to the electrode: (A) direct, (B) transport through electrically conductive nanowires, (C) indirect using mediators.
Figure 1. Electron transfer to the electrode: (A) direct, (B) transport through electrically conductive nanowires, (C) indirect using mediators.
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Figure 2. Stages of biofilm formation on anode in MFC.
Figure 2. Stages of biofilm formation on anode in MFC.
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Figure 3. Preparation of the activated coconut carbon to use in the MFC: 1—grains of activated coconut carbon; 2—hydrochloric acid solution (5%); 3—mixing ACC with acid solution; 4—separation of ACC from the acid solution; 5—ACC drying; 6—ACC prepared for use in MFC as an anode.
Figure 3. Preparation of the activated coconut carbon to use in the MFC: 1—grains of activated coconut carbon; 2—hydrochloric acid solution (5%); 3—mixing ACC with acid solution; 4—separation of ACC from the acid solution; 5—ACC drying; 6—ACC prepared for use in MFC as an anode.
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Figure 4. Electrodes: (A) carbon fibers anode (CFA), (B) anode chamber with activated coconut carbon with carbon fibers anode (ACCcfA), (C) stainless steel cathode (SSC), and (D) cathode chamber with SCC.
Figure 4. Electrodes: (A) carbon fibers anode (CFA), (B) anode chamber with activated coconut carbon with carbon fibers anode (ACCcfA), (C) stainless steel cathode (SSC), and (D) cathode chamber with SCC.
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Figure 5. Measurement position for analyzing MFC operation using various types of anodes: (A) types of used anode: 1—carbon fiber brush (CFA), 2—activated coconut carbon grans (ACCgA), 3—carbon fiber brush with activated coconut carbon (ACCcfA); (B) scheme of MFC used in research: 4—anode chamber, 5—cathode chamber, 6—anode, 7—sintered glass separator, 8—air bubbles, 9—cathode, 10—stone air bubbler, 11—air supply, 12—COD reduction measurements, 13—electrical parameters measurements; (C) view of MFC.
Figure 5. Measurement position for analyzing MFC operation using various types of anodes: (A) types of used anode: 1—carbon fiber brush (CFA), 2—activated coconut carbon grans (ACCgA), 3—carbon fiber brush with activated coconut carbon (ACCcfA); (B) scheme of MFC used in research: 4—anode chamber, 5—cathode chamber, 6—anode, 7—sintered glass separator, 8—air bubbles, 9—cathode, 10—stone air bubbler, 11—air supply, 12—COD reduction measurements, 13—electrical parameters measurements; (C) view of MFC.
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Figure 6. Cell voltage during MFC start-ups (for three various electrode configurations: CFA/SSC, ACCgA/SSC, and ACCcfA/SSC).
Figure 6. Cell voltage during MFC start-ups (for three various electrode configurations: CFA/SSC, ACCgA/SSC, and ACCcfA/SSC).
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Figure 7. Output cell voltage (of the MFCs for three various electrode configurations: ACCgA/SSC, CFA/SSC, and ACCcfA/SSC) in one cycle (A) of feeding the MDYP to MFC and in six cycles (B) of feeding the MDYP to MFC.
Figure 7. Output cell voltage (of the MFCs for three various electrode configurations: ACCgA/SSC, CFA/SSC, and ACCcfA/SSC) in one cycle (A) of feeding the MDYP to MFC and in six cycles (B) of feeding the MDYP to MFC.
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Figure 8. Power density curves (A), and polarization curves (B) obtained during MFC operation (MFC with three various electrode configurations: ACCgA/SSC, CFA/SSC, and ACCcfA/SSC).
Figure 8. Power density curves (A), and polarization curves (B) obtained during MFC operation (MFC with three various electrode configurations: ACCgA/SSC, CFA/SSC, and ACCcfA/SSC).
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Figure 9. COD reduction in MFCs with various electrode configurations (ACCgA/SSC, CFA/SSC, and ACCcfA/SSC): (A) in a full single cycle until the cell voltage disappears and (B) in six single cycles (110 h cycles).
Figure 9. COD reduction in MFCs with various electrode configurations (ACCgA/SSC, CFA/SSC, and ACCcfA/SSC): (A) in a full single cycle until the cell voltage disappears and (B) in six single cycles (110 h cycles).
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Table 1. Average cell voltage of MFC with various electrodes systems (in six cycles), the maximum power density, and the average efficiency of COD reduction (in six cycles) in the MFC with various electrodes systems.
Table 1. Average cell voltage of MFC with various electrodes systems (in six cycles), the maximum power density, and the average efficiency of COD reduction (in six cycles) in the MFC with various electrodes systems.
Electrode SystemAverage Cell Voltage
[mV]		Maximum Power Density
[mW·m–2]		Average COD Reduction
[%]
ACCgA/SSC55518
CFA/SSC2312326
ACCcfA/SSC2452633
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Włodarczyk, P.P.; Włodarczyk, B. Effect of Supporting Carbon Fiber Anode by Activated Coconut Carbon in the Microbial Fuel Cell Fed by Molasses Decoction from Yeast Production. Energies 2024, 17, 3607. https://doi.org/10.3390/en17153607

AMA Style

Włodarczyk PP, Włodarczyk B. Effect of Supporting Carbon Fiber Anode by Activated Coconut Carbon in the Microbial Fuel Cell Fed by Molasses Decoction from Yeast Production. Energies. 2024; 17(15):3607. https://doi.org/10.3390/en17153607

Chicago/Turabian Style

Włodarczyk, Paweł P., and Barbara Włodarczyk. 2024. "Effect of Supporting Carbon Fiber Anode by Activated Coconut Carbon in the Microbial Fuel Cell Fed by Molasses Decoction from Yeast Production" Energies 17, no. 15: 3607. https://doi.org/10.3390/en17153607

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