Microbial adaptation to biodegradation of tert-butyl alcohol in a sequencing batch reactor

Abstract

This study demonstrates the utility of the sequencing batch reactor (SBR) to adapt microorganisms towards biological removal of tert-butyl alcohol (TBA). The reactor was inoculated with activated sludge and fed with TBA as the sole carbon source. Start-of-cycle TBA concentrations were initially set at 100 mg L −1 with a cycle time of 24 h and a volumetric exchange ratio of 50% to maintain a TBA loading rate of not more than 100 mg L −1 d −1. Step increases in TBA loading rates up to 600 mg L −1 d −1 were achieved by first raising the start-of-cycle TBA concentration to 150 mg L −1 on day 90 and subsequently by reducing the cycle time from 24 to 12, 8 and 6 h on days 100, 121 and 199, respectively. This acclimation strategy favored the retention of increasingly higher densities of well-adapted microbial populations in the reactor. The increases in TBA loading produced better settling biomass and higher biomass concentrations with higher specific TBA biodegradation rates. Effluent TBA concentrations were consistently below the detection limit of 25 μg L −1. The use of progressively shorter cycle times created selection pressures that fostered the self-immobilization of the reactor microorganisms into aerobic granules which first appeared on day 125. Specific TBA biodegradation rates in the granules followed the Haldane model for substrate inhibition, and peaked at 13.8 mg TBA g VSS −1 h −1 at a TBA concentration of 300 mg L −1. Denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified 16S rRNA genes from granules sampled between days 220 and 247 confirmed the existence of a highly stable microbial community with members belonging to the α, β and δ subdivisions of Proteobacteria and the Cytophaga–Flavobacteria–Bacteroides (CFB) group.