Cr(VI) Reduction in Continuous-Flow Coculture Bioreactor

A continuous-flow coculture bioreactor with a phenol-degrading organism, Pseudomonas putida DMP-1, and a Cr(VI)-reducing species, Escherichia coli ATCC 33456, was developed for simultaneous removal of phenol and Cr(VI). Phenol was the sole energy and carbon source added to the coculture along with a basal medium and hexavalent chromium. The coculture bioreactor was operated under three liquid detention times (0.20, 0.31, and 0.52 days) with phenol and Cr(VI) loadings ranging from 2,500 to 8,200 mg/L/day and 4.5-33.2 mg/L/day, respectively. After 279 days of continuous operation, eight quasi-steady-state operation conditions were obtained with near complete removal of phenol and Cr(VI). Elevated levels of Cr(VI) and phenol were observed in the effluent under a high influent Cr(VI) concentration (16 mg/L) or a short liquid detention time (0.20 days). The system recovered from Cr(VI) toxicity after influent Cr(VI) level was reduced. Chromium mass balance analysis revealed that nearly all of the influent Cr(VI) was reduced to Cr(III) in the coculture bioreactor through biological activity. Spectra of UV-Vis and mass spectrometers suggested that phenol metabolites produced by P. putida were utilized by E. coli.