Design of a novel biohythane process with high H2 and CH4 production rates

A biohythane process based on wheat straw including: i) pretreatment, ii) H2 production using Caldicellulosiruptor saccharolyticus, iii) CH4 production using an undefined consortium, and iv) gas upgrading using an amine solution, was assessed through process modelling including cost and energy analysis. According to simulations, a biohythane gas with the composition 46–57% H2, 43–54% CH4 and 0.4% CO2, could be produced at high production rates (2.8–6.1 L/L/d), with 93% chemical oxygen demand (COD) reduction, and a net energy yield of 7.4–7.7 kJ/g dry straw. The model was calibrated and verified using experimental data from dark fermentation (DF) of wheat straw hydrolysate, and anaerobic digestion of DF effluent. In addition, the effect of gas recirculation was investigated by both wet experiments and simulation. Sparging improved H2 productivities and yields, but negatively affected the net energy gain and cost of the overall process.

► High productivity of H2 and CH4 can be obtained in a wheat straw based process.
► H2 productivities and yields were improved by sparging with the gas produced in anaerobic digestion.
► 99% of the CO2 can be removed by the proposed novel gas-upgrading system.
► The cost effectiveness of the process can be improved by reducing nutrient addition and avoiding sparging in the DF process.