Simultaneous chromium(VI) reduction and phenol degradation in an anaerobic consortium of bacteria

Simultaneous removal of Cr(VI) and phenol was investigated in an anaerobic consortium of bacteria supplemented with a Cr(VI)-reducing organism, Escherichia coli ATCC 33456. Neither E. coli nor the anaerobic phenol-degrading consortium culture was acclimated to Cr(VI) prior to the batch experiments. Optimum Cr(VI) reduction was observed at a phenol concentration of 200 mg/l at an initial Cr(VI) concentration of 2.0 mg/l. The interaction between E. coli and phenol-degraders was observed by varying initial concentrations of chromate, phenol and phenol-degrader/E. coli ratio in the anaerobic consortium. Higher phenol-degrader/E. coli ratios resulted in higher rates of Cr(VI) reduction. The highest observed cumulative Cr(VI) reduced per unit weight of metabolite utilized by E. coli (1.25 mg Cr(VI)/mg organic acids consumed) approximated the theoretical value (1.32 mg Cr(VI)/mg organic acids consumed). A positive correlation noted between phenol degradation and Cr(VI) reduction indicated that E. coli utilized metabolites formed from phenol degradation as electron donors for Cr(VI) reduction.