Modeling Removal of Air Contaminants by Biofiltration

A mathematical model was developed that describes basic transport and biological processes for a biofilter. The model described transfer between the air and solids/water phases, biological degradation of the substrate, CO 2 production and accumulation, and pH changes resulting from CO 2 accumulation. Model equations were solved using a two-step, explicit, finite difference approximation technique, and solutions were tested on simplified problems with known analytical results. Experimental data were compared with the predictive model solutions for steady-state and non–steady-state regimes. The effects of adsorption were separated from the effects of biodegradation by experiments using varying input contaminant concentrations. Laboratory experiments used compost, granular activated carbon, and a mixture of compost and diatomaceous earth as biofilter packing materials to treat ethanol vapors. While the adsorptive capacity of the granular activated carbon was substantially reduced by water and microbial growth, it remained highest for the three media. The compost microbial community had a higher degradation rate constant. Carbon provided the best treatment overall.