4. Conclusions The current study demonstrated that raw wet sc could be directly used for hydrogen fermentation without any further step for detoxification or drying. The analysis of gas production and metabolites indicated that initial pH and feedstock concentration greatly impacted hydrogen productivity, whereas heat treatment was found unnecessary for hydrogen production from the wet SC. A maximum hydrogen yield (10 Lkg 1 TS-1) and hydrogen con- tent (36.83%) were achieved under the optimized conditions at 200 g L-1 of substrate, initial pH of 6.5 and seed sludge without heat treatment. Furthermore, the two-stage biohythane process led to a maximum hydrogen yield of 12 Lkg 1 TS-1 and methane yield of 195 Lkg 1 TS 1, 26% higher in the total energy recovery than one stage biomethane fermentation with reduced fermentation time, indicating the potential ofthis method for harvesting clean hythane vehicle fuel from waste biomass.