Performance and microbial community analysis of two-stage process with extreme thermophilic hydrogen and thermophilic methane production from hydrolysate in UASB reactors

The two-stage process for extreme thermophilic hydrogen and thermophilic methane production from wheat straw hydrolysate was investigated in up-flow anaerobic sludge bed (UASB) reactors. Specific hydrogen and methane yields of 89 ml-H₂/g-VS (190 ml-H₂/g-sugars) and 307 ml-CH₄/g-VS, respectively were achieved simultaneously with the overall VS removal efficiency of 81% by operating with total hydraulic retention time (HRT) of 4 days . The energy conversion efficiency was dramatically increased from only 7.5% in the hydrogen stage to 87.5% of the potential energy from hydrolysate, corresponding to total energy of 13.4 kJ/g-VS. Dominant hydrogen-producing bacteria in the H₂-UASB reactor were Thermoanaerobacter wiegelii, Caldanaerobacter subteraneus, and Caloramator fervidus. Meanwhile, the CH₄-UASB reactor was dominated with methanogens of Methanosarcina mazei and Methanothermobacter defluvii. The results from this study suggest the two stage anaerobic process can be effectively used for energy recovery and for stabilization of hydrolysate at anaerobic conditions.