Two-stage thermophilic fermentation and mesophilic methanogen process for biohythane production from palm oil mill effluent

A two-stage thermophilic fermentation and mesophilic methanogenic process for biohythane production from palm oil mill effluent (POME) was investigated. The hydrogen and methane potential from POME were 170-200 L H2 kgCOD−1 and 210-292 L CH4 kgCOD−1, respectively. A continuous two-stage process with hydraulic retention time (HRT) of 2 d for hydrogen reactor and 15 d for methane reactor, obtained 34% higher energy yield than single stage methane production. The hydrogen and methane yields from two-stage were 210 L H2 kgCOD−1 and 315 L CH4 kgCOD−1, respectively with total energy yield of 15.34 MJ kgCOD−1. Mixed hydrogen and methane (biohythane) production rate was 4.4 L biogas L−1d−1 with containing of 51% CH4, 14% H2 and 35% CO2. Hydrogen reactor was dominated with hydrogen producing bacteria of Thermoanaerobacterium thermosaccharolyticum, while acetoclastic Methanoculleus sp. was the dominant methanogen in methane reactor. Two-stage process for biohythane production could efficiently for energy recovery from POME.