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.