Microbial community structure of ethanol type fermentation in bio-hydrogen production

Three continuous stirred-tank reactors (CSTRs) were used for H-2 production from molasses wastewater at influent pH of 6.0-6.5 (reactor A), 5.5-6.0 (reactor B), or 4.0-4.5 (reactor C). After operation for 28 days, the microbial community formed ethanol type (C), propionate type (A) and ethanol-butyrate-mixed type (B) fermentation. The H-2 production rate was the highest for ethanol type fermentation, 0.40 1 (g VSS)(-1) day(-1) or 0.45 I H-2 (9 COD removed)(-1). Microbial community dynamics and diversity were analysed using doublegradient denaturing gradient gel electrophoresis (DG-DGGE). Denaturing gradient gel electrophoresis profiles indicated that the community structures changed quickly in the first 14 days. Phylogenetic analysis indicated that the dominant bacterial groups were low G+C Gram-positive bacteria, Bacteroides, gamma-Proteobacteria and Actinobacteria; alpha-Proteobacteria, beta-Proteobacteria, delta-Proteobacteria and Spirochaetes were also presented as minor groups in the three reactors. H-2-producing bacteria were affiliated with Ethanoligenens, Acetanaerobacterium, Clostridium, Megasphaera, Citrobacter and Bacteroides. An ethanol-based H-2-producing bacterium, Ethanoligenens harbinense CGMCC1152, was isolated from reactor C and visualized using fluorescence in situ hybridization (FISH) to be 19% of the eubacteria in reactor C. In addition, isoenzyme activity staining for alcohol dehydrogenase (ADH) supported that the majority of ethanol-producing bacteria were affiliated with Ethanoligenens in the microbial community.