A review on bioelectrochemical systems: From mechanisms to applications in bioenergy, wastewater treatment, and biochemical production

Bioelectrochemical systems (BESs) are emerging technologies that integrate microbial metabolism with electrochemical processes to enable simultaneous biofuel production, wastewater treatment, and carbon valorisation. This review critically evaluates recent advances in BES platforms including microbial fuel cells, microbial electrolysis cells, microbial electrosynthesis systems, and microbial desalination cells, with a focus on their applications in fuel processing, low-carbon biorefineries, and circular resource utilisation. Key electrochemical and microbial mechanisms governing extracellular electron transfer, reactor performance, and system efficiency are discussed, highlighting the importance of electrode design, microbial community structure, and reactor configuration in determining BES performance. This review demonstrates that BESs can facilitate the conversion of wastewater, organic residues, and CO 2 into bioelectricity, hydrogen, methane, volatile fatty acids, alcohols, and biodegradable polymers. Microbial electrosynthesis in particular is identified as a promising technology for carbon capture and utilisation through the conversion of CO2 into fuels using renewable electricity. Integration with anaerobic digestion, electrocoagulation, membrane bioreactors, and carbon capture processes further illustrates the potential of BESs to enhance resource recovery whilst reducing energy demand and greenhouse gas emissions. Despite their potential, several critical barriers continue to limit large-scale implementation, including low power densities, electron transfer limitations, membrane fouling, high material costs, and challenges associated with reactor scalability and long-term operational stability. Future progress will therefore depend on advances in electrode materials, microbial engineering, reactor design, and technoeconomic optimisation. Overall, BESs demonstrate considerable potential as multifunctional platforms for sustainable fuel processing, wastewater remediation, and low-carbon chemical production.