ANALYTICAL MODEL OF DUAL-MEDIA BIOFILTER FOR REMOVAL OF ORGANIC AIR-POLLUTANTS

A steady-state mathematical model is presented to describe the kinetic s of volatile organic compound (VOC) removal in biofilters that consis t of a mixed compost and granular activated carbon (GAC) medium. The m odel describes the basic transport of VOCs from the gas phase into the liquid phase of the compost biofilm and into the carbon particles, us ing the assumptions of diffusion as characterized by Fick's law. The k inetics of biological degradation of substrate (pollutant) in the comp ost biofilm are assumed to follow a Monod-like relationship. Experimen tal data were compared with model predictions under steady-state condi tions for treatment of a mixture of benzene, toluene, ethylbenzene, an d o-xylene (BTEX) vapors. Best results were obtained when model applic ations were divided according to first-order biodegradation kinetics f or relatively low influent concentrations (<50 ppm) of pollutants and zero-order reaction for higher (235-440 ppm) influent concentrations. In both instances, the model produced suitable approximation of experi mental bed depth versus concentration profiles at steady state for ind ividual compounds in biofilters containing small but varying amounts o f GAC. The presence of GAC improved BTEX removal efficiencies over a b iofilter containing only compost.