Cometabolic degradation of chlorophenols by Acinetobacter species

Phenol-induced cells of Acinetobacter species were used to degrade 4- and 3-chlorophenols (CP). Several different patterns of batch 4- or 3-CP degradation were shown by cultures growing in different concentration ratios of phenol (growth substrate) to 4- or 3-CP, e.g. complete degradation of 4- or 3-CP at the depletion of phenol, partial 4- or 3-CP degradation at the depletion of phenol and inhibition of both phenol and 3-CP degradations. These patterns are characteristics of concentration-dependent substrate competition/inhibition between phenol and CP. As the initial concentration ratio of phenol/4-CP reduced, decreasing values of the cell growth yield were obtained from each batch experiment. Two different values of a critical concentration ratio were necessary to completely degrade 4- and 3-CP in the presence of phenol; below these ratios, the initial amount of 4- or 3-CP was only partially degraded. The 3-CP transformation product toxicity, as opposed to the absence in phenol/4-CP, might have accounted for the requirement of a higher critical phenol/3-CP concentration ratio than that for phenol/4-CP. Furthermore, higher COD accumulation (2.38 mg COD mg−1 3-CP vs 1.27 mg COD mg−1 4-CP) but less chloride release (0.13 mg Cl− mg−1 3-CP vs 0.26 mg Cl− mg−1 4-CP) was obtained in phenol/3-CP experiments. These results suggest that the cometabolic degradation pathways for 4- and 3-CP may differ at the monooxygenation step such that the overt 3-CP transformation product toxicity could be attributed to accumulation and autopolymerization of 3-chlorocatechol.