Microbial community analysis of anaerobic granules in phenol-degrading UASB by next generation sequencing

The objective of this study was to investigate microbial communities in a continuous anaerobic phenol-degrading system using a next generation sequencing tool. The anaerobic granules adapted to phenol were first obtained by repeated-batch operation, which were then inoculated in an up-flow anaerobic sludge blanket reactor (UASB) operated at various organic loading rates (OLRs). Lag periods for both phenol degradation and CH₄ production decreased as batch fermentation was repeated, indicating a progressive adaptation of the granules to phenol. In the UASB operation, the highest OLR handled was 6 kg COD/m³/d, in which the attained biogas production rate, phenol degradation, and CH₄ contents were 2.1 m³/m³/d, 79.0%, and 75.3%, respectively. Syntrophorhabdus and Clostridium were found to be the dominant bacteria, whose sum occupied around 60% of total bacterial sequences. In particular, there was a significant increase in Syntrophorhabdus (39.2% of total bacterial sequences), known to degrade phenol to benzoate and subsequently to acetate and hydrogen in syntrophic association with a hydrogenotrophic methanogen. In terms of archaea, Methanosaeta (42.1% of total archaeal sequences), and Methanobacterium (24.5% of total archaeal sequences) became dominant as operation continued, which were negligible in the inoculum.