Biohythane production from organic fraction of municipal solid waste: Clean and green energy generation under circular economy framework

Biohydrogen, with an energy content of 120-142 MJ/kg, offers a promising alternative to fossil fuels due to its high energy density and the environmentally benign byproduct-pure water. Among various hydrogen production technologies, dark fermentation (DF) stands out for its sustainability. DF is particularly advantageous due to its cost-effectiveness and ability to utilize a range of organic feedstocks, including the organic fraction of municipal solid waste (OFMSW), food waste, and sewage sludge, which are often available in abundance and at low cost. Dark fermentation combined with anaerobic digestion (AD) presents a dual benefit: it facilitates the production of both biohydrogen and biomethane (energy content, 50-55 MJ/kg), thus recovering two valuable energy carriers while simultaneously improving waste management for challenging waste streams. This integrated approach enhances resource recovery and supports sustainable waste management practices. Despite significant advancements in these technologies over recent decades, there is a lack of comprehensive reviews that integrate past and recent developments. This review aims to fill this gap by systematically compiling and analyzing the recent advancements in biohythane production. It covers key aspects including production pathways, process microbiology, and controlling factors. The review also compares single-, two- and three-stage processes, evaluate the effects of co-digestion of OFMSW with other wastes, and assess the impact of pretreatment methods on biohythane production. Challenges and future perspectives related to biohythane production are also discussed.