Pilot-scale two-stage process: A combination of acidogenic hydrogenesis and methanogenesis

This study was performed to optimize both acidogenic hydrogenesis and methanogenesis, and then to develop a pilot-scale two-stage process producing not only CH₄ but also H₂. Firstly, acidogenic hydrogenesis of food waste was examined in pilot-scale leaching-bed reactors using dilution rate (D) as a tool to improve the environmental conditions. The maximum efficiency of 71.4% was obtained by adjusting D from 4.5 to 2.5 d^-1 depending on the state of degradation. Secondly, the wastewater from acidogenic hydrogenesis was converted to CH₄ in a pilot-scale UASB reactor. The COD removal efficiency exceeded 95% up to the loading rates of 13.1 g COD/L /d, which corresponded to HRT of 0.25 d (6 h). Lastly, a pilot-scale two-stage process was devised based on a combination of acidogenic hydrogenesis and methanogenesis. Over 120 days, the pilot-scale process resulted in large VS reduction of 70.9% at the high loading rate of 12.5 kg VS/m³/d in a short SRT of 8 days.