Abstract
Immobilized growing cells were prepared by entrapment into PVA beads. Diffusion of azo dye Black B within the beads has been studied by measuring the transport of solutes to and from a well-stirred solution of limited volume in a batch system. A mathematical model of unsteady–state diffusion in a sphere was used with appropriate boundary conditions, and the effective diffusion coefficient of dye was found from the best fit of the experimental data using a computer regression analysis method. Tests have been performed with immobilized beads made from PVA covering a range of mixing speed, dye concentration, PVA fraction, cell fraction, and bead diameter. The external resistance to mass transfer is negligible when the mixing speed was 400 rpm or higher. Effective diffusion coefficients decreased considerably with increasing dye concentration, PVA fraction, cell fraction. The biodegradation kinetics of dye including biodegradation and diffusion together was studied in PVA immobilized beads as a function of particle size in a batch system. Both free and immobilized cells in 1.91 ~ 4.43 mm diameter particles were used and the reaction were achieved in a medium containing dye concentration 50 ~ 2000 mg/L. The results were analyzed according to Michaelis-Menten kinetics. For the free cells, the maximum reaction rate and Michaelis-Menten constants were determined as Vm=212.8 mg dye/g dry cell/hr, Km=305 mg dye/L, respectively. For immobilized cells in 1.91 ~ 4.43 mm diameter particles, Vm=130 mg dye/g dry cell/hr, Km,app=432, 475, 505, 548, 595 mg dye/L, intrinsic Km=318 mg dye/L, respectively. Using these values, effectiveness factors were calculated from matlab program as η=0.7 ~0.58. The satisfactory agreement between the calculated values and the experimental results of dye concentration in solution supports the validity of Km, Vm, De and Kp.