Analysis of xenobiotic bioremediation in a co-immobilized mixed culture system

Abstract

The existence of an oxygen gradient within a biocatalyst was examined with application towards the mineralization of a xenobiotic. A mathematical model is presented for the coupled anaerobic and aerobic biodegradation of xenobiotics by a co-immobilized system. A previous study by Beunink and Rehm (Appl. Microbiol. Biotechnol., 34 (1990) p. 108) demonstrated that a coupled reductive and oxidative degradation of the xenobiotic 4-chloro-2-nitrophenol (CNP) was observed with co-immobilization of the facultative anaerobe, Enterobacter cloacae, and the obligate aerobe, Alcaligenes sp. TK-2. Based on the fitting parameters, the model simulations were carried out in both batch and continuous reactor modes. Simulation results indicated that xenobiotic degradation was highly dependent upon the solid size, cell loading, solids fraction, the bulk oxygen concentration, and cellular maintenance coefficient for oxygen. For the specific system examined, an optimum particle size for the primary and intermediate xenobiotic mineralization in the continuous reactor mode was in the range of 0.1–0.3 cm diameter. The mineralization was maximized at the largest cell loading and solids fractions simulated in the continuous reactor mode. Simulation results indicated that the coupled anaerobic/aerobic degradation in a single reactor may be an alternative to the two-stage anaerobic/aerobic biodegradation of xenobiotics.