CO-IMMOBILIZED NITROSOMONAS-EUROPAEA AND NITROBACTER-AGILIS CELLS - VALIDATION OF A DYNAMIC-MODEL FOR SIMULTANEOUS SUBSTRATE CONVERSION ANDGROWTH IN KAPPA-CARRAGEENAN GEL BEADS

A dynamic model for two microbial species immobilized in a gel matrix is presented and validated with experiments. The model characterizes t he nitrification of ammonia with Nitrosomonas europaea and Nitrobacter agilis co-immobilized in kappa-carrageenan gel beads. The model consi sts of kinetic equations for the microorganisms and mass transfer equa tions for the substrates and products inside and outside the gel beads . The model predicts reactor bulk concentrations together with the sub strate consumption rate, product formation, and biomass growth inside the gel beads as a function of time. A 50-day experiment with immobili zed cells in a 3.3-dm(3) air-lift loop reactor was carried out to vali date the model. The parameter values for the model were obtained from literature and separate experiments. The experimentally determined rea ctor bulk concentrations and the biomass distribution of the two micro organisms in the gel beads were well predicted by the model. A sensiti vity analysis of the model for the given initial values indicated the most relevant parameters to be the maximum specific growth rate of the microorganisms, the diffusion coefficient of oxygen, and the radius o f the beads. The dynamic model provides a useful tool for further stud y and possible control of the nitrification process. (C) 1994 John Wil ey & Sons, Inc.