Modeling Cr(VI) reduction and phenol degradation in a cocoulture biofilm reactor

A transient-state model was developed to simulate simultaneous Cr(VI) reduction and phenol degradation by a coculture of Cr(VI)-reducing/phenol-degrading bacteria growing on glass bead surfaces in a fixed-film bioreactor. The coculture consisted of the Cr(VI) reducers, Escherichia coli ATCC 33456, and the phenol degraders, Pseudomonas putida DMP-1. Phenol was supplied as the sole added carbon source and electron donor. The model simulated cell growth kinetics with E. coli utilizing metabolites formed from phenol degradation in P. putida as carbon sources. Substrate utilization and Cr(VI) reduction in the fixed-film bioreactor was represented by a system of (second-order) partial differential equations (PDEs). The PDE system was solved by the fourth-order Runge-Kutta method adjusted for mass transport resistance by the second-order Crank-Nicholson and backward Euler methods. A heuristic procedure, genetic search algorithm, was used to optimize the model against experimental data. The model predicted effluent concentration with 98.6% confidence for Cr(VI), 93.4% confidence for phenol, and 88.3% confidence for metabolites. Parameters determined showed higher Cr(VI) and phenol removal kinetics in the biofilm system than previously observed in batch systems.