Aggregation of immobilized activated sludge cells into aerobically grown microbial granules for the aerobic biodegradation of phenol

Aims: The aim of this study is to evaluate the utility of aerobically grown microbial granules for the biological treatment of phenol‐containing wastewater. Methods and Results: A column‐type sequential aerobic sludge blanket reactor was inoculated with activated sludge and fed with phenol as the sole carbon source, at a rate of 1·5 g phenol l −1 d −1 . Aerobically grown microbial granules first appeared on day 9 of reactor operation and quickly grew to displace the seed flocs as the dominant form of biomass in the reactor. These granules were compact and regular in appearance, and consisted of bacterial rods and cocci and fungi embedded in an extracellular polymeric matrix. The granules had a mean size of 0·52 mm, a sludge volume index of 40 ml g −1 and a specific oxygen utilization rate of 110 mg oxygen g VSS −1 h −1 (VSS stands for volatile suspended solids). Specific phenol degradation rates increased with phenol concentration from 0 to 500 mg phenol l −1 , peaked at 1·4 g phenol g VSS −1 d −1 , and declined with further increases in phenol concentration as substrate inhibition effects became important. Conclusions: Aerobically grown microbial granules were successfully cultivated in a reactor maintained at a loading rate of 1·5 g phenol l −1 d −1 . The granules exhibited a high tolerance towards phenol. Significant rates of phenol degradation were attained at phenol concentrations as high as 2 g l −1 . Significance and Impact of the Study: This is the first study to demonstrate the ability of aerobically grown microbial granules to degrade phenol. These granules appear to represent an excellent immobilization strategy for microorganisms to biologically remove phenol and other toxic chemicals in high‐strength industrial wastewaters.