Biohythane Production from Organic Wastes by Two-Stage Anaerobic Fermentation Technology

The combination of biohydrogen and biomethane production from organic wastes via two-stage anaerobic fermentation could yield a biohythane gas with a composition of 10-15% H2, 50-55% CH4 and 30-40% CO2. Biohythane could be upgraded to biobased hythane by removing of CO2. The two-stage anaerobic fermentation process is based on the different function between acidogens and methanogens in physiology, nutrition needs, growth kinetics, and sensitivity to environmental conditions. In the first stage, the substrate is fermented to H2, CO2, volatile fatty acids (VFA), lactic acid and alcohols by acidogens with optimal pH of 5–6 and hydraulic retention time (HRT) of 1–3 days. In the second stage, the remaining VFA, lactic acid, and alcohols in the H2 effluent are converted to CH4 and CO2 by methanogens under optimal pH range of 7–8 and HRT of 10–15 days. The advantage of biohythane over traditional biogas are more environmentally, flexible of H2/CH4 ratio, higher energy recovery, higher degradation efficiency, shorter fermentation time, and high potential to use as vehicle fuel. This chapter outlines the general approach of biohythane production via two-stage anaerobic fermentation, principles, microorganisms, reactor configuration, process parameters, methods for improving productivity as well as technical challenges toward the scale-up process of biohythane process.