Toxicity effect of phenol on aerobic granules

Aerobic granular sludge cultivated in a pilot-scale sequencing batch reactor, through mechanical separation using metal sieves, was categorized into five size categories of0.09 (flocs), 0.35, 0.82, 1.65 and 2.54 mm in mean diameter. Granule microbial activiy of each size category and the activity of the sludge flocs were determined after exposure to phenol (0-3000 mg L(-1)) at various exposure times of 4, 12, and 24 hours. The microbial activity reduction follows a linear relationship with the increase in phenol concentration for both granules and sludge flocs. The C50 value, i.e., the phenol concentration causing 50% inhibition of the microbial activity, decreased significantly with the exposure time, but it increased with granule size. The C50 increased by 18% from 1273 mg L(-1) for sludge flocs to 1497 mg L(-1) for granules of size 2.54 mm at an exposure time of 24 hours. The results indicated that the granular structure could protect the microbial cells from phenol toxicity. The application of aerobic granules in wastewater treatment could provide an improved ability to tolerate toxic chemical shock, particularly at longer exposure times.