Simultaneous chromium(VI) reduction and phenol degradation in a fixed-film coculture bioreactor: reactor performance

Simultaneous Cr(VI) reduction and phenol degradation was observed in a fixed-film bioreactor consisting of a coculture of phenol-degrading bacteria, Pseudomonas putida DMP-1, and Cr(VI)-reducing bacteria, Escherichia coli ATCC 33456. Near complete Cr(VI) reduction and phenol degradation was observed during steady-state operation of the reactor under loadings of 5–21 mg Cr(VI) l−1 d−1 and 840–3350 mg phenol l−1 d−1. 2-hydroxymuconic semialdehyde (2HMSA), succinate, and acetate were the detected steady-state organic acid metabolites which accounted for 13–23% of TOC in the effluent. Optimum Cr(VI) reduction rate was observed under a Cr(VI) loading of approximately 26.5 mg Cr(VI) l−1 d−1 just before system overload. System overload was characterized by the increase in effluent Cr(VI) and phenol concentrations. System resilience to Cr(VI) toxicity was demonstrated by rapid recovery of biological activity and reduced effluent Cr(VI) and phenol concentrations after off-loading the system from overloaded conditions.