Journal of Energy Bioscience 2024, Vol.15, No.3, 186-196 http://bioscipublisher.com/index.php/jeb 189 additional oxidizing agents like hydroxyl radicals (•OH) are generated in situ to enhance the degradation of refractory pollutants (Sathe et al., 2021). 3.3 Performance metrics: COD removal efficiency, energy output, etc. Performance metrics for MFCs in wastewater treatment are typically evaluated based on COD removal efficiency, energy output, and other specific removal efficiencies. For instance, COD removal efficiencies as high as 96.3% have been reported in MFC systems treating petroleum refinery wastewater, with corresponding energy recoveries of up to 0.002 58 kWh/m³ (Yang et al., 2020). Similarly, combined photoelectrocatalytic MFCs (PEC-MFCs) have achieved COD removal efficiencies of 96% for phenol and 70% for aniline, while also producing significant amounts of electricity. In continuous mode operations, MFCs treating refinery wastewater have demonstrated power densities of (225±1.4) mW/m² and substrate degradation rates of (1.05±0.01) kg COD/m³-day (Srikanth et al., 2016). These metrics highlight the dual benefits of MFCs in both pollutant removal and energy recovery, making them a viable option for sustainable wastewater treatment. 4 Energy Recovery Mechanisms 4.1 Bioelectrochemical pathways for energy generation The bioelectrochemical pathways in MFCs are driven by the metabolic activities of microorganisms that oxidize organic matter in wastewater, releasing electrons and protons. These electrons are transferred to the anode and flow through an external circuit to the cathode, generating electricity. The integration of microalgae in MFCs, forming microalgae-microbial fuel cells (mMFCs), further enhances this process by utilizing photosynthesis to convert light energy into biochemical energy, which is then converted into electricity (Kusmayadi et al., 2020). Additionally, the use of MFCs as biosensors in combined systems, such as MFC-MBR (membrane bioreactor), has shown to improve process control and energy recovery, with a maximum energy recovery of 0.002 58 kWh m-3, five times higher than control systems (Zhao et al., 2021). 4.2 Optimization of electrode materials for enhanced energy recovery The performance of MFCs is significantly influenced by the materials used for electrodes. Optimizing these materials can lead to enhanced energy recovery. For example, non-platinum (non-Pt) electrodes in a scalable MFC stack have demonstrated high power output and efficient wastewater treatment under continuous flow conditions (Zhuang et al., 2012). The choice of catholyte also plays a crucial role; ferricyanide catholytes have been shown to produce higher power outputs compared to aerated catholytes, with significant improvements in power density and current generation (Mohan et al. 2008; Mohan et al., 2009). Furthermore, the use of glass wool as a proton exchange membrane (PEM) in single-chambered MFCs has been evaluated, showing that operating conditions such as pH and organic loading rates can markedly influence power output and substrate degradation efficiency. 4.3 Role of biofilms in electron transfer processes Biofilms, which are communities of microorganisms that adhere to the anode surface, play a critical role in the electron transfer processes in MFCs. These biofilms facilitate the transfer of electrons from the microbial cells to the anode, enhancing the overall efficiency of electricity generation. The formation and maintenance of biofilms are influenced by various factors, including the nature of the substrate and the operating conditions. Studies have shown that biofilms can significantly improve the performance of MFCs by increasing the rate of electron transfer and reducing internal resistance (Srikanth et al., 2016; Zhang et al., 2019). Additionally, the microbial community within the biofilm, including nitrifiers and denitrificans, contributes to simultaneous pollutant degradation and power recovery, as observed in air-cathode MFCs treating low C/N ratio wastewater (Yang et al., 2021). 5 Technological Advancements 5.1 Innovations in MFC design for improved efficiency Recent advancements in microbial fuel cell (MFC) technology have focused on optimizing various parameters to enhance efficiency and power output. Innovations include optimizing reactor configurations, electrode construction, and the addition of redox-active mediators to improve electron transfer processes (Li et al., 2018). Additionally, the integration of anaerobic acidification and forward osmosis membranes into MFCs has shown
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