The anaerobic biodegradability and toxicity of fourteen aromatic compounds were evaluated over a wide range of concentrations using a serum bottle technique. Benzene, toluene, and all three isomers of xylene were not significantly degraded to methane in a phenol-enriched culture. Complete degradation of 1000 mg/L phenol, 800 mg/L catechol, 100 mg/L 2-NP, 100 mg/L 3- NP, and 100 mg/L 4-NP was observed within two months while depletion of 100 mg/L resorcinol and 1000 mg/L hydroquinone required more than six and eight months incubation, respectively. None of the three isomers of chlorophenol were degraded in the phenol-enriched culture. Batch toxicity assay revealed that the phenol-enriched culture was more susceptible to inhibition caused by substituted phenols than the acetate-enriched culture. In general, the inhibitory effects on both phenol degradation and acetate utilization did not vary significantly with the isomer but rather with the substituted group. The degree of inhibition was in the order of nitrophenols \u3e chlorophenols \u3e hydroxyphenols. The Haldane inhibition model was used to fit experimental data from phenol and catechol. The inhibition of phenol degradation by chlorophenols, resorcinol, and hydroquinone was described rather well by a Monod-type, noncompetitive model
