Mathematical Model of Biofiltration of VOCs: Effect of Nitrate Concentration and Backwashing

Abstract

The affect of nitrate concentration and reactor backwashing on biofilter performance is evaluated using a dynamic mathematical model of the biodegradation process of volatile organic compounds in a trickle bed biofilter packed with uniform synthetic solids. Experimental observations from a bench-scale biofilter system treating ether were used to develop and validate the model. Experience acquired in biofiltration of volatile organic compounds has demonstrated that although these two factors—nitrate and backwashing—are secondary when organic packing material is used, they are essential when the packing media is synthetic. The operation of a synthetic media packed reactor requires the addition of nutrients necessary for biodegradation. Since nitrate was utilized as the nitrogen source in this system, it was included in the model as a limiting substrate (nutrient). A negative affect of excessive accumulation of biomass in the reactor on biofilter performance has also been observed in highly loaded synthetic media biofilters. This problem was solved by removing excessive biomass via full media fluidization and backwashing of the reactor. The affect of periodic backwashing was included in the model as a reduction in the biofilm thickness and a new approach to calculate the reactor specific surface area after backwashing. The unknown model parameters that correspond to nitrate limitations were estimated. The mathematical model was then used for simulation and analyses of the affect of these two factors on the biodegradation process.