Microbiological aspects of microbial electrolysis cells: Isolation, screening, and electron transfer mechanisms

Biohydrogen is a leading candidate in the global shift toward renewable energy, offering a sustainable solution to reduce reliance on fossil fuels. This review underscores the use of microbial electrolysis cells (MECs) as a viable strategy to address increasing energy demands. In MECs, extracellular electron transfer (EET) is a vital mechanism that enables microorganisms to channel electrons (e⁻) from organic donors to external acceptors. Exo-electrogenic bacteria, viz., Geobacter, Shewanella, Pseudomonas, Nitrospira, and Desulfovibrio, are frequently reported for their ability to utilize Iron: Fe (III) and Manganese: Mn (III/IV) as electron acceptors, which can be replaced with electrodes to drive proton reduction and hydrogen (H₂) generation. The use of renewable substrates in fermentation processes further strengthens the commercial feasibility of biohydrogen production, while the molecular traits of microbes provide insights into optimizing H₂ production. Despite encouraging laboratory-scale demonstrations, challenges persist due to variability in recovery methods and the limited microbial diversity explored. Expanding the repertoire of exo-electrogens and refining MEC configurations are critical to achieving higher yields. Overall, biohydrogen stands out as a clean, eco-friendly energy resource, with microbial electrolysis offering a sustainable energy technology.