Rapid cultivation of stable aerobic phenol-degrading granules using acetate-fed granules as microbial seed

The aim of this study is to evaluate the utility of using aerobic acetate-fed microbial granules as a starting seed to rapidly develop stable aerobic phenol-degrading granules. Aerobic granules were first cultivated in four sequencing batch reactors with acetate as sole carbon source at a loading rate of 3.8 kg m−3 d−1. Phenol was then added to reactors R1, R2, R3 and R4 at loading rates of 0, 0.6, 1.2 and 2.4 kg m−3 d−1, respectively. The granules acclimated quickly to the phenol loading, and stabilized only 1 week after phenol was introduced. The granules exhibited good settling ability with good biomass retention and good metabolic activity, as evidenced by the low SVI values, stable biomass concentrations and good removal of acetate and phenol. No significant inhibitory effects from phenol toxicity were observed at the intermediate loadings of 0.6 and 1.2 kg phenol m−3 d−1, except for a slight lag in the ability of the granules to degrade phenol during the initial cycles. At the highest loading of 2.4 kg phenol m−3 d−1, a sharp buildup of phenol was observed in reactor R4 because the granules were initially unable to degrade phenol. However, this buildup quickly dissipated as the granules adapted rapidly to the high phenol concentrations. The compact structure of the acetate-fed granules likely protected the microorganisms against phenol toxicity and facilitated microbial acclimation towards faster phenol degradation rates. This is the first study to demonstrate the benefits of using aerobic granules cultivated on benign substrates as microbial seed to produce granules to degrade toxic substrates. This concept of using granules to produce different granules can be extended to granule-based applications involving other toxic chemicals and other types of high-strength industrial wastewaters, where rapid reactor start-up and system stability are key considerations.