Performance of fermentative hydrogen production and microbial community in ACR at different influent COD concentrations

The operation performance of fermentative hydrogen production in anaerobic contact reactor (ACR) at different influent COD concentrations was investigated. The ACR could be kept at steady-state with ethanol-type fermentation, as influent chemical oxygen demand (COD) increased from 7000 mg·L^-1 to 11000 mg·L^-1 with constant HRT of 6 h. Specific hydrogen production of the ACR system increased from 2.43 m³·(m³·d)^-1 to 3.51 m³·(m³·d)^-1 as influent COD increased from 7000 mg·L^-1 to 11000 mg·L^-1, while specific hydrogen production of activated sludge peaked at 10.71 mol H₂·(kg VSS·d)^-1 at influent COD of 9000 mg·L^-1. The results of polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) profiles showed that hydrogen-producing ethanol fermentative bacteria were dominant in the ACR. As influent COD concentration increased, Ethanoligenens harbinense YUAN-3 became more abundant, and propionate fermentative bacteria, i. e. Propionicimonas sp. F6 also started to be enriched.