MATHEMATICAL MODEL AND PARAMETER ESTIMATION FOR TREATMENT OF VOCS IN TRICKLE-BED BIOFILTERS

摘要

The main features of a fundamental mathematical model of the biodegradationrnprocess of VOCs in a trickle bed biofilter packed with uniform synthetic solids arernanalyzed. Some aspects of the model are based on well-known and establishedrntheories while others are new, and are developed as a response to experimentalrnobservations. The dynamic model considers two limiting substrates, VOC and nitrate,rnand two types of biomass, active and inactive. The system has three phases, biofilm,rnwater, and gas. The variables calculated in the model are: limiting substratesrnconcentration, biomass distribution in the biofilm, and biofilm thickness. Experimentalrnobservations from a bench-scale biofilter system treating diethyl ether (C_2H_5OC_2H_5)rnwith nitrate as the sole nitrogen source are used to calibrated and validated the model.rnThe unknown model parameters are estimated using nonlinear parameter estimationrntechniques. The estimation is done in three stages: estimates of the steady staternmodel parameters are obtained first, then, these values are used in the estimation ofrnthe parameters of the dynamic model. Finally, nitrate limitations are included in thernmodel and the parameters corresponding to nitrate consumption are estimated. Thernmathematical model is then used for simulation and analysis of the biodegradationrnprocess. Experimental observations showed that excessive accumulation of biomassrnin the reactor has a negative effect on contaminant removal efficiency. To solve thisrnproblem, excess biomass is removed via full media fluidization and backwashing ofrnthe biofilter. The effect of periodic backwashing of the reactors is included in thernmodel as a reduction in the biofilm thickness and an adjustment of the calculatedrnspecific surface area of the reactor after backwashing. Model simulations of thernbiofilter performance with time predict the deterioration in biofilter performance due tornbiomass accumulation and its improvement due to backwashing.