Microbial Electrolysis Cells for the Treatment of Dye Effluent and Coupled with Generation of Hydrogen

Dyes find extensive use in industries such as textiles, leather, and cosmetics, but their discharge poses a significant environmental risk. Bioelectrochemical methods for treating dye wastewater offer an environmentally friendly and economically viable solution, embraced by numerous scientists. Microbial electrolysis cells (MECs) have emerged as a promising technology for azo dye treatment and simultaneous hydrogen gas production. MECs employ an anaerobic biocathode where exoelectrogens catalyze the breakdown of azo bonds, generating hydrogen gas. These cells exhibit rapid decolorization and mineralization of a wide range of azo dyes. Importantly, the bioelectrochemical reduction process prevents the accumulation of harmful aromatic amine intermediates, a common issue in anaerobic digestion. MECs operate efficiently under neutral pH and ambient temperatures, and their simultaneous wastewater treatment and hydrogen production improve overall economics. However, MECs face challenges such as substrate competition with organic materials, exoelectrogen sensitivity to dye toxicity, and the potential for methane formation. Successful deployment requires biocathode acclimation, reactor configuration optimization, electrode material selection, voltage adjustment, and co-substrate supply. While MECs have demonstrated high decolorization efficiency, overcoming obstacles related to intermediate mineralization and scalability is crucial for practical application. Integration with photocatalysis or aerobic polishing can effectively address intermediate byproducts. Techno-economic analyses highlight the promising potential of MECs for sustainable azo dye wastewater treatment and bioenergy generation. Realizing this potential necessitates further research on exoelectrogen acclimation, reactor design, and large-scale trials.