Start-up, microbial community analysis and formation of aerobic granules in a tert-butyl alcohol degrading sequencing batch reactor

We demonstrate that compact well-settling aerobic granules can be developed in a sequencing batch reactor (SBR) for the biological removal of tert-butyl alcohol (TBA) using a strategy involving step increases in TBA loading rate achieved through increasing TBA concentrations in the influent. A moderate selection pressure that included a cycle time of 24 h and a start-of-cycle TBA concentration of 100 mg/L was initially introduced to encourage the growth and retention of biomass and avoid biomass loss from hydraulic washout. Start-of-cycle TBA concentrations were increased to 150, 300, 450, and 600 mg/L on days 90, 100, 121, and 199, respectively. These increases were only introduced after complete TBA removal was accompanied by visible improvements in biomass concentration and biomass settling ability. This acclimation strategy produced incrementally higher biomass concentrations and better settling biomass with higher specific TBA biodegradation rates. Effluent TBA concentrations were consistently below the detection limit of 25 mu g/L. Aerobic granules were first observed about 180 days after reactor start-up. The granules had a clearly defined shape and appearance, settled significantly faster than the suspended sludge in the reactor, and eventually became the dominant form of biomass in the reactor. The adapted granules were capable of complete TBA removal and contained a stable microbial population with a low diversity of sequences of community 16S rRNA gene fragments. This study indicates that it is possible to use aerobic granules for TBA remediation and will contribute to a better understanding of how microbial acclimation can be exploited in the SBR to biologically remove recalcitrant xenobiotics.