HEXAVALENT CHROMIUM DETOXIFICATION IN A FULLY INTEGRATED COCULTURE BIOFILM REACTOR: A MODEL INCORPORATING BIOMASS AND METABOLITE KINETICS
A model was developed based Cr(VI) reduction by the Cr(VI)-reducing bacteria, Escherichia coli ATCC 33456, growing on metabolites formed from phenol degradation by Pseudomonas putida DMP-1 in a bench-scale, packed-bed bioreactor system. Metabolites analysis in the coculture system showed that the predominant metabolites were the six-carbon 2-hydroxymuconic semialdehyde (2-HMSA) and four-carbon succinic acid, both of which were readily assimilated into the E. coli cells' metabolic pathways. This indicated that phenol degradation followed a truncated meta-pathway and switched over to the β-ketoadipate (ortho-cleavage) pathway. The model developed in this study was unique in that full cell growth dynamics and inhibition kinetics were considered together with the substrate utilization, Cr(VI) reduction, and cell inactivation kinetics under transient-state operation conditions. The model simulated time variation of the six state-variables (phenol concentration, P, viable P. putida cell density, X p , metabolites concentration, U, viable E. coli cell density, X E , inactivated cell density, X I, and Cr(VI) concentration, C). 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. The system was optimized by a modified Sugal genetic search algorithm (Hunter 1998). The model behaved similarly for the pure culture and coculture systems. At the time of this study, the developed model was still unstable during phase changes when Cr(VI) loading was increased either by increasing the concentration or by increasing the flow rate. An adaptive step function was incorporated to moderate the effects of the sudden changes in inputs on algorithm stability (Press et al., 2000). The final model successfully captured the observed trends in effluent Cr(VI) and substrate concentration in response to changes in influent conditions.
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Document Type: Research Article
Publication date: 2005-01-01
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