Sustainable Bioelectricity: Transformation of Chicha de Jora Waste into Renewable Energy

Abstract

Corn is one of the most widely produced cereals worldwide, generating large amounts of waste, represents an environmental and economic challenge. In regions such as Africa and rural areas of Peru, access to electricity is limited, affecting quality of life and economic development. This study proposes using microbial fuel cells (MFCs) to convert chicha de jora waste—a traditional fermented beverage made from corn—into electrical energy. Single-chamber MFCs with activated carbon (anode) and zinc (cathode) electrodes were used. A total of 100 ml of chicha de jora waste was added in each MFC, and three MFCs were used in total. The MFCs demonstrated the viability of chicha de jora waste as a substrate for bioelectricity generation. Key findings include a notable peak in voltage (0.833 ± 0.041 V) and current (2.794 ± 0.241 mA) on day 14, with a maximum power density of 5.651 ± 0.817 mW/cm². The pH increased from 3.689 ± 0.001 to 5.407 ± 0.071, indicating microorganisms’ degradation of organic acids. Electrical conductivity rose from 43.647 ± 1.025 mS/cm to 186.474 ± 6.517 mS/cm, suggesting ion release due to microbial activity. Chemical oxygen demand (COD) decreased from 957.32 ± 5.18 mg/L to 251.62 ± 61.15 mg/L by day 18, showing efficient degradation of organic matter. Oxidation-reduction potential (ORP) increased, reaching a maximum of 115.891 ± 4.918 mV on day 14, indicating more oxidizing conditions due to electrogenic microbial activity. Metagenomic analysis revealed Bacteroidota (48.47%) and Proteobacteria (29.83%) as the predominant phyla. This research demonstrates the potential of chicha de jora waste for bioelectricity generation in MFCs, offering a sustainable method for waste management and renewable energy production. Implementing MFC technology can reduce environmental pollution caused by corn waste and provide alternative energy sources for regions with limited access to electricity.

1. Introduction

Corn is the most produced cereal worldwide, with global production reaching approximately 1224.3 million tons in the years 2023–2024 [1]. This high consumption generates significant waste, posing environmental and economic challenges [2]. Millions of tons of corn waste are produced yearly, with a global direct cost of waste management estimated at USD 252 billion in 2020 [3]. Including the hidden costs of pollution, unhealthiness, and climate change, this value rises to USD 361 billion [4]. According to the United Nations, municipal solid waste generation, including agricultural waste, is projected to increase from 2.30 to 3.08 billion tons in 2026 to 2050 [2].

Electricity access remains a significant challenge in poor countries, affecting quality of life and economic development [5]. Over 759 million people lack electricity access, with minimal access in regions like Sub-Saharan Africa, and approximately 2 million Peruvians are still without electricity [6]. The most affected regions are Loreto, Ucayali, Madre de Dios, and Amazonas, cities far from the capital [7]. Although Peru has great potential for renewable energy, it still relies heavily on fossil fuels such as natural gas and diesel for electricity generation [8]. In this sense, microbial fuel cells (MFCs) represent an emerging technology with great potential in sustainable energy production, where microorganisms are used to decompose organic matter (organic waste) and generate electricity, which makes them attractive for environmental and energy applications [9,10]. Organic waste has excellent potential for use as substrates in MFCs; for example, Verma and Mishra (2023), in their research, managed to generate maximum power density peaks of 86.9 ± 0.4 mW/m² using banana waste as a substrate [11]. Similarly, Mulyono et al. (2022) used vegetable waste as a substrate in their MFCs, showing a maximum voltage of 0.804 V with an electric current of 2.37 mA [12]. In their research, Yang et al. (2021) used watermelon peel waste as a substrate, generating maximum values of 0.294 V with a power density of 13.6 W/m³ [9]. MFCs should not be considered independent energy sources due to their limited power output. Instead, their true potential lies in combined applications, such as electricity generation alongside wastewater treatment, addressing the removal of organic pollutants and heavy metals [10]. Various studies have highlighted this dual functionality, including the work published by Liu et al. (2025), which optimizes MFC utilization, positioning them as a sustainable tool for energy recovery and environmental remediation in waste management and water treatment scenarios [13].

The chicha de jora is a traditional fermented drink of Andean origin, and it is especially popular in Peru, Ecuador, and Bolivia [14]. It is made from jora, which is malted corn (germinated and dried), and has a slightly acidic and refreshing taste [15]. In Peru, it has been reported that for every 10 kg of corn, approximately 50 L of chicha de jora can be produced, depending on the size of the fermentation vessel [16]. The increase in production has meant a rise in the waste generated from the fermentation process until sale [17]. There is no information in the current literature on the use of chicha de jora waste as a substrate in microbial fuel cells, and due to the high organic load present, it can be an excellent candidate for use as a substrate in MFCs.

This study evaluates the potential of chicha de jora waste as a substrate in single-chamber microbial fuel cells with carbon and zinc electrodes. Various parameters were examined, such as electric current, current density, power density, voltage, pH, and electrical conductivity. Likewise, the internal resistance of the microbial fuel cells will be determined. The microorganisms attached to the anodic electrode will also be molecularly identified. Using chicha de jora waste in MFCs will help reduce the amount of organic waste that would otherwise end up in landfills, contributing to environmental pollution. MFCs can convert organic waste into electricity, providing a renewable energy source, which aligns with global efforts to reduce dependence on fossil fuels and promote sustainable energy sources. Implementing MFC technology can create new economic opportunities, particularly in rural areas where waste management and energy production can be integrated.

2. Materials and Methods

a.

Design and assembly of the MFCs

The single-chamber microbial fuel cells (MFCs) used in this study were commercially purchased from anode provided a highly porous surface to facilitate bacterial adhesion and electron transfer, while the zinc cathode ensured efficient electron reception for the completion of the electrochemical reaction. The electrodes had respective surface areas of 24 cm² for the anode and 16.62 cm² for the cathode, ensuring an optimal reaction interface for microbial activity and energy transfer. The electrodes were separated by a fixed distance of 10 cm, a crucial parameter influencing the internal resistance and overall performance of the system. A 100 Ω external resistor was integrated into the external circuit, serving to regulate and optimize the electron flow. The electrical connections were established using 0.5 mm thick copper wires, ensuring minimal resistance losses and maximum conductivity throughout the circuit.

To facilitate proton transfer while maintaining separation between the anode and cathode chambers, a Nafion™ proton exchange membrane was employed. This membrane plays a vital role in selectively allowing proton migration while preventing direct contact between electrodes, thus enhancing electrochemical efficiency. Figure 1 illustrates the schematic representation of the energy generation process, demonstrating the microbial conversion of chicha de jora waste into bioelectricity. The chicha de jora waste used as substrate was collected from the Santo Dominguito market in Trujillo, Peru. A total of 0.900 L of waste material was acquired and preserved at a controlled temperature of 20 °C until its introduction into the microbial fuel cells. Each MFC was then inoculated with precisely 100 mL of chicha de jora waste to maintain consistency across trials. To ensure data reliability, three single-chamber MFCs were used for each measured parameter, with values averaged and standard deviations calculated for accuracy in performance evaluation.

b.

Operationalization of the MFCs

The microbial fuel cells (MFCs) were assembled with the anode fixed at the center of the lid and the cathode sealing the opposite end. Each MFC was filled with 100 mL of chicha de jora waste, maintaining a stable laboratory ambient temperature of 21 °C. To ensure efficient electron transfer, the external circuit was connected using tin electrodes and 8 mm copper wires, which were precisely soldered. A 100 Ω external resistor was integrated into the system to regulate the current flow. Current (I) and voltage (V) values were measured at regular intervals using a Truper MUT-830 digital multimeter, enabling detailed monitoring of electrochemical activity. To assess the system’s efficiency in organic matter removal, chemical oxygen demand (COD) was quantified following the closed reflux colorimetric method according to NTP 360.502:2016. The internal resistance of the MFCs was determined using a Vernier energy sensor, capable of measuring ranges of ±30 V and ±1000 mA, providing essential data on system losses. Power density (PD) and current density (CD) were calculated using the methodology proposed by Afrin et al. (2024) [17], facilitating a quantitative evaluation of bioelectrochemical performance. All experiments were conducted in triplicate to ensure reproducibility and minimize variability in results.

c.

Prokaryotic community structure in chicha de jora waste residues by 16S RNA gene analysis

Under sterile laboratory conditions, an electrode sample was carefully collected from the chicha de jora waste to minimize contamination during handling. The sample was then transported under a controlled cold chain protocol to Ecobiotech Lab S.A.C., ensuring optimal preservation of DNA integrity for subsequent analysis. Genomic DNA extraction was performed using the E.Z.N.A.^® Soil DNA kit (Omega Bio-Tek Inc., Norcross, GA, USA), following the manufacturer’s optimized protocol to maximize yield and purity. The extracted DNA was then quantified using an EzDrop1000 Blue-Ray Biotech microvolume spectrophotometer (Santiago, Chile), allowing precise concentration measurement and purity assessment. For long-term stability, the DNA samples were stored at −30 °C until further analysis.

Aliquots of the extracted DNA were later sent to MR DNA (Molecular Research LP, Shallowater, TX, USA) for sequencing of the 16S rRNA gene using the bTEFAP^® Illumina Diversity Assay technology. This high-throughput sequencing approach provided a comprehensive profile of the microbial diversity present in the chicha de jora waste sample. Taxonomic classification and abundance percentages were determined using the Mothur software package (1.48.0), a widely recognized tool for microbial community analysis. The processed data were further organized and analyzed using Excel Professional Plus 2019 to ensure accurate visualization and interpretation of results.

3. Results and Analysis

The voltage values obtained through the monitoring are shown in Figure 2. An increase is observed from the first day (0.102 ± 0.001 V) to the 14th day (0.833 ± 0.041 V), followed by a decrease until the last day (0.698 ± 0.056 V). The voltage values tend to vary over time due to the successive increase in the potential differential between the electrodes created by the chemical compounds in the initial state of operation of the MFCs [18]. The decrease is due to the sediment of the inorganic compounds in the MFC, which causes an incomplete degradation of these compounds, which limits the availability of substrate for microorganisms, affecting the potential differential [18]. Yaqoo et al. (2022) [19] used food waste from a cafeteria as fuel in their MFCs, managing to generate 2.9 V on the twentieth day, mentioning that a high organic load can initially increase the potential differential. Still, if it is excessive, it can saturate the system and reduce efficiency [19]. Halim et al. (2025) managed to generate voltage peaks of 0.112 V using wastewater as a substrate in their MFCs, mentioning that as the MFC operates, the substrate is depleted, and microorganisms can enter a stationary or decline phase, which reduces the power differential [20].

The electric current values recorded by the MFC are shown in Figure 3. The initial value of the MFC on the first day (0.028 ± 0.010 mA) increases until reaching a value of 2.794 ± 0.241 mA on day 14 and then decreases until day 18 (2.358 ± 0.293 mA). The electrical current curve reflects changes in microbial metabolism. In the initial phase, microorganisms are in an active growth state, utilizing metabolic pathways that maximize energy production. As resources become depleted, they may switch to less efficient metabolic pathways or enter a dormant phase. The efficiency of an MFC depends on the microorganisms’ ability to convert substrates into electricity. A decrease in current indicates a reduction in this efficiency, which may be caused by nutrient depletion, inhibition due to waste products, or biofilm degradation [21,22]. Idris et al. (2024) used vegetable waste as fuel in their MFCs, generating 0.163 mA on day 22, mentioning that vegetable-derived waste contains carbohydrates, alcohols, and other organic compounds that microorganisms can ferment and oxidize, and as these compounds degrade, electron generation decreases, reducing the electric current [18]. Likewise, Rokhim et al. (2024) used rice, vegetable, and fruit waste in their MFCs as substrates, showing an electric current of 11.5 mA, mentioning that the production of organic acids, alcohols, or toxic compounds could affect the electron transfer efficiency and that the formation of biofilm on the electrode could improve or hinder this transfer over time [23].

The pH values start at 3.689 ± 0.001, indicating an acidic medium in the first days of the experiment due to the fermented nature of chicha de jora, which contains organic acids. As time progresses, the pH increases progressively until day 14, when the MFCs show their optimal operating values (5.407 ± 0.071) (see Figure 4a). This increase in pH values is related to microorganisms’ degradation of organic acids in the substrate [24]. Furthermore, substrate degradation may be affected by pH variations, as many metabolic pathways rely on optimal pH conditions to function effectively [25]. At pH outside this range can slow down degradation rates, reducing the availability of electrons for current generation. Therefore, maintaining a controlled pH not only ensures maximum microbial activity but also enhances electrical production and overall MFC efficiency [22]. The metabolic activity of electrogenic bacteria in the microbial fuel cell can also influence this change [26]. Fadzli et al. (2021) [26] used yam waste in their MFCs, where the substrate operated at a pH of 5.17, generating 32 mV. They mentioned that microorganisms can use acidic compounds as a source of carbon and energy, reducing the medium’s acidity [19]. Likewise, Yaqoob et al. (2022) [19] used rambutan, langsat, and mango waste as substrates in their MFCs, which operated at a pH of 6.50, managing to generate peaks of 0.490 V, and, in turn, they mentioned that during microbial metabolism, specific processes can create compounds that increase the pH, such as ammonia or carbonates [19]. Figure 4b shows the values of electrical conductivity, where the values start at 43.647 ± 1.025 mS/cm and increase to about 186.474 ± 6.517 mS/cm on day 14; this increase is due to the release of ions into the solution, a product of the metabolic activity of microorganisms and the degradation of organic compounds in the substrate [20]. A comparative analysis of electrical conductivity values with those reported in the literature could provide clearer insights into the relative performance of current MFCs. For instance, recent studies have examined how electrical conductivity impacts MFC efficiency, emphasizing parameters such as current density and power density. Comparing these values with similar systems in the literature can help identify areas for improvement, such as optimizing electrode materials or refining operational conditions [21]. Fermentation and bacterial metabolism can generate salts, acids, and other ionic compounds that improve the medium’s conductivity. In the slight decrease phase, after the maximum peak, it may be due to the consumption of nutrients and the precipitation of compounds, and as the microorganisms consume the available substrates, the concentration of free ions in the medium may be reduced [20,26]. Hussain et al. (2022) used waste from a cafeteria in their MFCs, where the substrates showed an electrical conductivity of 1746 mS/cm, managing to generate voltage peaks of 0.416 V and mentioning that when the medium has a high conductivity, electron transport and system efficiency improves [22]. Likewise, Kamperidis et al. (2022) used food waste as a substrate in their MFCs, showing an electrical conductivity of 5 ± 0.6 mS/cm, mentioning that the precipitation of compounds or formation of biomass that retains some ions affects the conductivity of the substrate [27]. Figure 4c shows the COD values, where the system starts with a high COD (957.32 ± 5.18 mg/L), which is expected due to the high organic load of the chicha de jora waste; this value indicates the amount of organic matter present in the medium, which microorganisms can use as an energy source [28]. The relationship between the reduction of chemical oxygen demand and microbial activity can be explored in terms of energy generation within an MFC [20]. As microorganisms break down organic compounds, the electrons released during this metabolic process are transferred to the anode, driving current generation. A greater reduction in COD indicates more efficient substrate degradation, resulting in a higher availability of electrons for electrochemical transfer [22,28]. Then, a constant reduction of the COD is observed over time, reaching values below 251.62 ± 61.15 mg/L on day 18; this reduction indicates that microorganisms are consuming the organic matter, transforming it into biomass, electrons, and metabolic byproducts [29]. Korojdeh et al. (2024) used grape waste as a substrate in their MFCs, where they managed to reduce the COD by 72%, mentioning that the decrease in COD suggests that microorganisms are using the organic compounds as a substrate, which results in the production of electrons and the generation of current in the MFC [30]. Savvidou et al. (2022) mentioned in their research that as biodegradable compounds are reduced, energy generation efficiency could decrease if a new substrate is not added and that factors such as pH, conductivity, and oxygen availability at the cathode can influence the efficiency of degradation [31]. In Figure 4d, a constant increase in the oxidation-reduction potential (ORP) values is observed from 28.024 ± 0.514 mV to a maximum of 115.891 ± 4.918 mV on day 14; this increase indicates a transition to more oxidizing conditions, possibly due to the activity of electrogenic microorganisms that are transferring electrons to the anode of the MFC [32]. Between days 12 and 18, a stabilization is shown to then observe a slight decrease; the decrease in the substrate (available organic compounds) that feeds the microbial activity and accumulation of metabolic products can alter the conditions of the system [33]. There is also a possible depletion of oxygen in the cathodic zone, affecting electron transport efficiency [34]. When ORP values become more positive, it may indicate a decrease in the activity of electrogenic microorganisms, potentially due to the accumulation of oxidation products, substrate depletion, or the presence of less favorable conditions for anaerobic metabolism [25]. This shift could reduce electron transfer and, consequently, electrical current generation. Therefore, monitoring and controlling ORP values not only enables the real-time assessment of microbial activity but also serves as a tool by which to optimize the operational conditions of MFCs [22]. This includes adjusting parameters such as substrate supply, electron flow, or even the medium’s characteristics to maintain an optimal redox environment that maximizes energy output [30].

Figure 5a shows the power density (PD) as a function of the current density (CD) of a microbial fuel cell using chicha de jora waste as a substrate. The power density increases with the current density until reaching a maximum near 5.651 ± 0.817 mW/cm²; then, the power density decreases with the increasing current density, indicating a drop in performance due to limitations such as internal resistance or substrate depletion [35]. While the voltage progressively decreases with increasing current density, a typical behavior in fuel cells due to the ohmic drop and activation losses and the decreasing trend of voltage suggests that at high current densities, the cell experiences higher internal losses [36]. Zafar et al. (2024) used kitchen waste as a substrate in their MFCs, managing to generate a power density of 221 mW/m², and they mention that microorganisms can use substrates containing fermentable sugars and organic compounds, but the substrate concentration affects electron production; i.e., a very low or high concentration can reduce efficiency [37]. Du H. and Shao Z. (2022) used potato waste as a substrate in MFCs, managing to generate a power density of 14.1 mW/m², and they mention that pH values outside the optimal range (generally between 6 and 8) can inhibit bacterial activity and that electrodes with high conductivity (such as graphite, activated carbon, or doped materials) improve electron transfer [38]. Figure 5b shows the voltage versus current (V-I) curve used to determine the internal resistance (Rint) of chicha de jora waste-based microbial fuel cells. The analysis is based on the linear relationship between voltage and current, where the internal resistance is obtained from the slope of the curve, where a Rint of 19.794 ± 1.243 Ω was calculated. Verma et al. (2024) managed to calculate an internal resistance of 285 Ω using banana peel as a substrate in their MFCs, and they mention that a dense and well-adhered biofilm improves electron transfer and reduces resistance, and that low microbial activity or a weak biofilm increases the internal resistance [39]. Yaakop et al. (2023) used wastewater as substrates in their MFCs, generating a maximum power density of 0.047 mW/m² [40]. They mention reducing the distance between the anode and the cathode to minimize ohmic resistance, as well as ensuring good oxygenation at the cathode to improve oxygen reduction and adjusting the electrolyte concentration to optimize ionic conductivity and thus power density [40]. Electrogenic microorganisms are responsible for transferring electrons from the substrate to the anode, and their metabolic activity can directly influence the components of internal resistance, such as ohmic resistance, charge transfer resistance, and diffusion resistance [25]. In the case of corn fermentate, its composition, rich in organic compounds, can serve as an efficient substrate for microorganisms, promoting the formation of biofilms on the anode [36]. These biofilms not only facilitate electron transfer but can also reduce charge transfer resistance. However, factors such as the accumulation of waste products or heterogeneity within the microbial community may increase internal resistance, limiting the overall efficiency of the MFC [27,33].

Numerous studies have been conducted that have revealed a remarkable diversity of microbial communities in organic waste types, which can impact the microbial ecology of ecosystems near agricultural areas [41]. These microbial communities have the potential to contaminate farming areas and negatively affect human health [41]. According to the sequence analysis of the 16S ARNs 16S, complex microbial communities were discovered in the chicha de jora waste sample obtained (see Figure 6). Mainly, three bacterial phyla, five classes, eight orders, nine families, and ten bacterial species were identified. Within, the most abundant phyla is Bacteroidota (48.47%), followed by Proteobacteria (29.83%), while the most abundant class is Bacteroidia (48.46%), which maintains a high presence through its dominance in the Bacteroidota phylum. While in the order, the most abundant is Bacteroidales (47.60%), in the genus, it was also Bacteroides, with 47.59%, followed by Acetobacter, with 21.31%. The most abundant family found was Bacteroidaceae, with 47.60%, and the most abundant species was Caproiciproducens sp., with 5.70%.

Similar research has shown that Bacteroidota and Proteobacteria bacteria are common in fruit waste, while Firmicutes predominates in agricultural crop plants [33,38]. In addition, the Bacteroidia class is found in corn waste, where it has been observed to play an essential role in the decomposition of lignocellulosic biomass. These bacteria are known for their ability to degrade complex carbohydrates and contribute to the composting process and processing of organic waste [42]. Also, the Acetobacter genus is found in corn waste, which can play an essential role in decomposing organic waste [43]. In particular, Acetobacter pasteurianus has been identified as a key bacterium responsible for the aerobic decomposition of corn silage under warm and humid conditions [44]. The Caproiciproducens species is a genus of bacteria that has been studied for its ability to produce volatile fatty acids, particularly caproic acid (also known as hexanoic acid), from the fermentation of organic matter, such as corn waste [45]. These bacteria are relevant in biorefinery and circular economy processes as they can convert agricultural waste into high-value compounds [46]. Figure 7 illustrates an innovative and sustainable method for generating bioelectricity from agricultural waste, specifically waste from the production of chicha de jora. This approach not only helps to manage waste efficiently but also contributes to the production of renewable energy. The connection of multiple MFCs in series generates a voltage of 2.28 V, which is sufficient to turn on an LED light, evidencing the output of electricity from the microbial degradation of the waste. This suggests a scalable approach to increasing energy production, which could have applications in rural communities or the food processing industry.

4. Conclusions

The present study highlights the untapped potential of chicha de jora waste as a substrate for microbial fuel cells (MFCs), providing a compelling solution to both agricultural waste management and renewable energy production. The findings indicate that microbial activity peaks around day 14, achieving optimal bioelectrochemical conversion efficiency before substrate depletion begins to reduce performance metrics. The sustained pH increase reflects the effective degradation of organic acids, while the consistent reduction in COD confirms the microorganisms’ ability to efficiently process organic matter into usable energy. Notably, the observed increase in ORP underscores the activity of electrogenic microorganisms, which is further validated by the peak power density of 5.651 ± 0.817 mW/cm² and an internal resistance of 19.794 ± 1.243 Ω. These values demonstrate that the system is capable of moderate yet promising electron transfer efficiency. Furthermore, microbial diversity analysis reveals the dominance of Bacteroidota and Proteobacteria, suggesting a microbial consortium highly adaptable to the electrogenic environment.

This study demonstrates the potential of chicha de jora waste as a viable substrate for microbial fuel cells (MFCs), offering a sustainable approach to both waste management and bioelectricity generation. Despite its promise, scaling MFC systems remains challenging due to factors such as cost, electrode fouling, and limited energy output. To enhance their applicability, future research should focus on improving Coulombic efficiency (CE), implementing electrode cleaning strategies to mitigate fouling, and exploring cost-effective materials without compromising electrochemical performance.

Additionally, expanding experimental data, including detailed analysis of electrogenic microbiota and validation of anomalous results, will strengthen the reproducibility and scientific rigor of this study. Refining the MFC application narrative and comparing findings with similar agricultural waste-based systems will provide a clearer perspective on its practical impact. With substantial revisions addressing these aspects, this work could contribute significantly to bioelectrochemical research and the development of sustainable energy solutions.