Parameter Estimation in Biofilter Systems

Abstract

The purpose of this research is to estimate the unknown parameters of a mathematical model of the biodegradation of volatile organic compounds (VOCs) in a gas phase trickle-bed biofilter, using experimental results from a two-reactor pilot-scale system treating the VOC diethyl ether. The model considers a dynamic three-phase system, (biofilm, water, and gas), nonuniform bacterial population, and one limiting substrate. The nonlinear parameter estimation was done in two stages: estimates of the steady-state model parameters were obtained first, and then, these values were used in the estimation of the remaining parameters. Experimentally obtained biofilter performance curves and batch tests were used for the estimation of the steady-state parameters: maximum rate of substrate utilization (μmXf/Y), Monod constant (Ks), and biofilm/water diffusivity ratio for ether, rd. Dynamic biofilter performance data were used to obtain the estimates of the six remaining parameters: yield coefficient (Y). maximum growth rate (μm), rate of decay (kd), rate of biomass maintenance (b), initial fraction of active biomass (fa0 = Xf/ρs), and coefficient of detachment (Cdet). Using the biofilter performance curves, the value of μmXf/Y was uniquely determined, but the estimates of the parameters Ks and rd were highly correlated. High values of Ks and rd gave similar results as low values of both parameters. Batch tests using the bacterial population from the reactor and ether as the only substrate were used to determine the value of Ks without diffusional interferences.