Biohydrogen production through dark fermentation from waste biomass:Current status and future perspectives on biorefinery development

Green and clean hydrogen production has become a significant focus in recent years to achieve sustainable renewable energy fuel needs. Biohydrogen production through the dark fermentation (DF) process from organic wastes is advantageous with its environmentally friendly, energy-efficient, and cost-effective characteristics. This article elucidates the viability of transforming the DF process into a biorefinery system. Operational pH, temperature, feeding rate, inoculum-to-substrate ratio, and hydrogen partial pressure and its liquid-to-gas mass transfer rate are the factors that govern the performance of the DF process. Sufficient research has been made that can lead to upscaling the DF process into an industrial-scale technology. However, the DF process cannot be upscaled at the current technology readiness level as a stand-alone technology. Hence, it requires a downstream process (preferably anaerobic digestion) to improve energy recovery efficiency and economic viability. The article also discusses the possible hydrogen purification and storage techniques for achieving fuel quality and easy accessibility. The article further tries to unfold the opportunities, challenges, and current scenario/future research directions to enhance hydrogen yield and microbial metabolism, depicting the commercialization status for biorefinery development. Finally, the current progress gaps and policy-level loopholes from the Indian perspective are highlighted by analyzing the strengths, weaknesses, opportunities, and threats

Development of stabilization methods using a pilot scale anaerobic digester for seasonal variations in kitchen wastes for improved methane production with zero breakdowns

Anaerobic digestion of kitchen waste faces the challenge of frequent composition variation and rapid digester acidification due to its highly degradable nature. Considering this challenge, one year long pilot scale anaerobic digestion study was conducted in the anaerobic digester of 25 ​m3/day capacity with seasonal kitchen waste (fruits and vegetable waste). The seasonal variation in kitchen waste content was studied by dividing a year into six seasons (each season comprising 60 days), namely, spring, summer, monsoon, autumn, early winter, and prevernal winter. Considering all the properties of kitchen waste, the anaerobic digestion experiment was conducted with the organic loading rate (OLR) of 0.60–0.72 ​kg VS/m3/day. The specific biogas production for all the seasons was found to be 0.56–0.68 ​m3/kg VS, with the volumetric methane content of 54.3–62.8%. The average seasonal specific methane production was observed in the range of 0.30–0.41 ​m3/kg VS. The anaerobic digestion conversion efficiency of 55.3–67.0% was found for the anaerobic digestion of the wastes. The problem of the rapid acidification of kitchen waste has been rectified with the addition of protein-rich de-oiled pongamia cake in place of alkali chemicals. The economic analysis of kitchen waste based anaerobic digestion showed the maximum economic benefits of biogas production as INR 30,783 for its utilization as LPG and INR 37,777 for its utilization as electricity for the summer season compared to all other seasons. The extra economic benefits earned by the utilization of the digested slurry as organic manure, as it contains a good amount of nitrogen (N) 2.3–2.6%, phosphorus (P) 0.6–0.9%, and potassium (K) 0.7–1.1%