Effects of ozonation on the biodegradability of substituted phenols

The aerobic biodegradability of unoxidised and ozonated chloro-, nitro-, and amino-phenols was investigated using batch bioassays with unacclimated biomass. Chloro- and nitro-phenols exhibited biorecalcitrant behavior at 200 mg/liter as COD, yet were more readily degraded at 30 mg/liter as COD. Ozonation of chloro- and nitro-phenols significantly enhanced their biodegradability. While unoxidized aminophenols were readily degradable, ozonation significantly decreased their biodegradability. Quantitative structure activity relationships (QSARs) using Hammett constants were developed for biodegradability of unoxidized substituted phenols. For the eight substituted phenols studied, ozonation significantly decreased the Microtox toxicity of each, with EC50 values increasing from 0.7 to 1.6 orders-of-magnitude.