Journal of Energy Bioscience 2024, Vol.15, No.3, 186-196 http://bioscipublisher.com/index.php/jeb 188 2 Principles of Microbial Fuel Cells 2.1 Detailed explanation of the working mechanism of MFCs The working mechanism of MFCs begins with the microbial oxidation of organic substrates at the anode. Electroactive bacteria, such as Geobacter and Shewanella species, metabolize the organic matter, releasing electrons and protons. The anode, typically made of conductive materials like carbon cloth or graphite, collects the electrons and channels them through an external circuit to the cathode, creating an electric current. The protons generated at the anode migrate through a proton exchange membrane to the cathode. At the cathode, a reduction reaction occurs, where the electrons, protons, and an electron acceptor (usually oxygen) combine to form water. This process not only generates electricity but also aids in the degradation of organic pollutants in wastewater (Srikanth et al., 2016; Kumar et al., 2019). 2.2 Key components: anode, cathode, and microbial catalysts The key components of MFCs include the anode, cathode, and microbial catalysts. The anode is where the oxidation of organic matter occurs, facilitated by electroactive bacteria. Materials commonly used for anodes include carbon-based materials such as graphite, carbon cloth, and carbon paper, which provide a large surface area for microbial colonization and electron transfer. The cathode is the site of the reduction reaction and is typically made of materials like platinum or nitrogen-doped graphene, which serve as catalysts for the oxygen reduction reaction. The microbial catalysts, or electroactive bacteria, play a crucial role in the MFC process by oxidizing the organic substrates and transferring the electrons to the anode. These bacteria can form biofilms on the anode surface, enhancing the efficiency of electron transfer (Liu et al., 2013; Moqsud et al., 2013). 2.3 Types of MFCs used in wastewater treatment Several types of MFCs have been developed for wastewater treatment, each with unique configurations and operational modes. Single-chamber MFCs, which have a single compartment for both the anode and cathode, are simple and cost-effective but may suffer from oxygen diffusion to the anode. Dual-chamber MFCs, with separate anode and cathode compartments connected by a proton exchange membrane, offer better control over the electrochemical environment but are more complex and expensive. Tubular MFCs, which use a cylindrical design, provide high scalability and are suitable for continuous flow operations. Integrated systems, such as the combined microbial fuel cell-membrane bioreactor (MFC-MBR) and photoelectrocatalytic microbial fuel cell (PEC-MFC), enhance wastewater treatment efficiency and energy recovery by combining MFCs with other treatment technologies (Zhang et al., 2019; Zhao et al., 2021). 3 Wastewater Treatment with MFCs 3.1 Specific pollutants and contaminants targeted by MFCs Microbial Fuel Cells (MFCs) have emerged as a promising technology for wastewater treatment, targeting a variety of specific pollutants and contaminants. MFCs have been effectively used to degrade emerging contaminants (ECs) such as dyes, pharmaceuticals, and pesticides, which are often bio-refractory and pose significant environmental risks (Sathe et al., 2021). Additionally, MFCs have shown efficacy in treating petroleum refinery wastewater, which contains high levels of chemical oxygen demand (COD), ammonium nitrogen (NH4 +-N), and total nitrogen (TN) (Zhao et al., 2021). Other specific pollutants targeted by MFCs include phenol, aniline, oil, grease, and sulfide, which are commonly found in industrial effluents (Srikanth et al., 2016; Zhang et al., 2019). 3.2 Electrochemical reactions involved in pollutant degradation The electrochemical reactions involved in pollutant degradation within MFCs are complex and multifaceted. In the anodic chamber, organic matter is oxidized by electrochemically active bacteria, releasing electrons and protons. These electrons travel through an external circuit to the cathode, generating electricity, while the protons migrate through a proton exchange membrane to the cathode. In the cathodic chamber, various reduction reactions occur, such as the reduction of oxygen to water or the reduction of other electron acceptors like ferricyanide (Mohan et al., 2019). In some advanced configurations, such as the bio-electro-Fenton MFC (BEF-MFC),
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