Closing the loop on biohydrogen production: A critical review on the post-fermentation broth management techniques

Abstract

The emergence of sustainability concepts within the energy sector has prompted a heightened interest in exploring alternative avenues to meet global energy demands. The embracement and integration of SDG 7 as a pivotal objective for the future energy landscape have spurred the development of comprehensive frameworks aimed at embedding sustainability principles within the energy sector's core fabric. In this pursuit of sustainable energy solutions, bio-hydrogen has emerged as a promising waste-to-energy concept, serving as a bridge between SDG 6 and SDG 7, thereby addressing both waste management and energy production imperatives. Among the diverse array of methods, biomass fermentation stands out as an effective approach, wherein waste streams derived from industrial and municipal sources can be utilized as feedstock for biohydrogen fermentation. While this approach exemplifies a step towards a circular economy, the treatment of the fermentation broth poses significant challenges, primarily due to the generation of bio-hazardous and toxic effluents. The fermentation broth is replete with microbial species, metabolites, organic compounds, and inorganic residues, rendering direct discharge untenable due to the adverse environmental and ecological ramifications. Consequently, the treatment and management of fermentation effluent have emerged as formidable techno-economic barriers inhibiting the industrial-scale upscaling of biohydrogen production processes, prompting widespread attention within the research community. This review aims to elucidate the various practices employed in post-fermentation broth treatment and management, shedding light on current methodologies, and highlighting areas for future advancement, particularly towards achieving zero liquid discharge from hydrogen fermentation processes.