MODELING AND EVALUATION OF AN INTEGRATED NITROGEN REMOVAL SYSTEM WITHMICROORGANISMS CO-IMMOBILIZED IN DOUBLE-LAYER GEL BEADS

A dynamic model describing integrated nitrification and denitrificatio n by Nitrosomonas europaea and Pseudomonas sp. co-immobilized in the s eparate layers of double-layer gel beads is presented. The model descr ibes diffusion of components, substrate utilization, and growth, all o ccurring simultaneously in the beads. Both internal and external mass transfer resistance are accounted for. The model predicts biomass and solute bulk concentrations, substrate consumption rates, product forma tion rates, and biomass and solute concentration profiles within the b eads as a function of time. Fluctuations in substrate load, dilution r ates, or mass transfer parameters can be accommodated as well. Intrins ic kinetic parameters of the microorganisms, internal and external mas s transfer coefficients, initial conditions, bead concentration, and p article diameters are the input parameters. The model was evaluated by comparing experimental and predicted bulk concentrations and macrosco pic consumption (production) rates in air-lift loop reactors containin g double-layer gel beads. The reactors were run under both steady and dynamic operating conditions. Nitrification rates were determined by d aily analysis of influent and effluent ammonia and nitrite concentrati ons, and denitrification rates were calculated from molecular nitrogen production rates measured by head-space analysis. Model predictions a greed reasonably well with the experimental results. Fluctuations in d ilution rates and influent substrate concentrations were adequately de scribed. Although further validation is still required, the model pres ented here has shown to describe satisfactorily the proposed system.