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

The existence of an oxygen gradient within a biocatalyst was examined with application towards the mineralization of a xenobiotic. A mathematical mode l is presented for the coupled anaerobic and aerobic biodegradation of xeno biotics by a co-immobilized system. A previous study by Beunink and Rehm (A ppl. Microbiol. Biotechnol., 34 ( 1990) p. 108) demonstrated that a coupled reductive and oxidative degradation of the xenobiotic 4-chloro-2-nitrophen ol (CNP) was observed with co-immobilization of the facultative anaerobe, E nterobacter cloacae, and the obligate aerobe, Alcaligenes sp. TK-2. Based s n the fitting parameters, the model simulations were carried out in both ba tch and continuous reactor modes. Simulation results indicated that xenobio tic degradation was highly dependent upon the solid size, cell loading, sol ids fraction, the bulk oxygen concentration, and cellular maintenance coeff icient for oxygen. For the specific system examined, an optimum particle si ze for the primary and intermediate xenobiotic mineralization in the contin uous reactor mode was in the range of 0.1-0.3 cm diameter. The mineralizati on was maximized at the largest sell loading and solids fractions simulated in the continuous reactor mode. Simulation results indicated that the coup led anaerobic/aerobic degradation in a single reactor may be an alternative to the two-stage anaerobic/aerobic biodegradation of xenobiotics. (C) 1998 Elsevier Science S.A.