Abstract
The structure of a microbial community during a two-phase circulating process for the hydrogen and methane fermentation of potato was investigated using a molecular biological approach. The process was performed using a mixing tank, a thermophilic acidogenic reactor (55°C) and a mesophilic methanogenic reactor (36°C) connected in series with the recirculation of methanogenic mixed liquor to the mixing tank. A continuous experiment was conducted by changing the process hydraulic retention time (HRT) stepwise from 56 days to 30 days, then 20 days and 15 days. A stable and high-rate hydrogen and methane fermentation was possible at a process HRT of 20 days with a hydrogen production rate of 3.6 l·l-1·d-1 and a methane production rate of 3.4 l·l-1·d-1. Denaturing gradient gel electrophoresis (DGGE) with 16S rRNA gene-targeted polymerase chain reaction (PCR) analysis was employed to identify the structure of a microbial community at various conditions for each reactor. Thermoanaerobacterium thermosaccharolyticum and Clostridium sporosphaeroides were considered to be the major hydrogen-producing bacteria in the thermophilic acidogenic reactor, whereas Methanosarcina siciliae and Methanoculleus bourgensis were considered, respectively, to be the acetate-utilizing and hydrogen-utilizing methanogenic archaea in the mesophilic methanogenic reactor.
