The relationship between instability of H2 production and compositions of bacterial communities within a dark fermentation fluidised‐bed bioreactor

Abstract

Microbial community composition dynamics was studied during H₂ fermentation from glucose in a fluidised‐bed bioreactor (FBR) aiming at obtaining insight into the H₂ fermentation microbiology and factors resulting in the instability of biofilm processes. FBR H₂ production performance was characterised by an instable pattern of prompt onset of H₂ production followed by rapid decrease. Gradual enrichment of organisms increased the diversity of FBR attached and suspended‐growth phase bacterial communities during the operation. FBR bacteria included potential H₂ producers, H₂ consumers and neither H₂ producers nor consumers, and those distantly related to any known organisms. The prompt onset of H₂ production was due to rapid growth of Clostridium butyricum (99–100%) affiliated strains after starting continuous feed. The proportion trend of C. butyricum in FBR attached and suspended‐growth phase communities coincided with H₂ and butyrate production. High glucose loading rate favoured the H₂ production by Escherichia coli (100%) affiliated strain. Decrease in H₂ production, associated with a shift from acetate–butyrate to acetate–propionate production, was due to changes in FBR attached and suspended‐growth phase bacterial community compositions. During the shift, organisms, including potential propionate producers, were enriched in the communities while the proportion trend of C. butyricum decreased. We suggest that the instability of H₂ fermentation in biofilm reactors is due to enrichment and efficient adhesion of H₂ consumers on the carrier and, therefore, biofilm reactors may not favour mesophilic H₂ fermentation. Biotechnol. Bioeng. 2007;97: 742–758.