Treatment of air streams contaminated with volatile organic compounds in a
biofilter under transient and steady-state conditions of operation is descr
ibed with a mathematical model. The model incorporates convection and dispe
rsion in the gas phase, partial coverage of the solid support, interphase m
ass transfer between the gas and the aqueous biofilm with an equilibrium pa
rtition at the interface followed by diffusion, direct adsorption to the ex
posed uncovered solid adsorbent media, transfer between the biofilm and the
solid support, and biological reactions in both the biofilm and the adsorb
ent. The model equations were solved numerically by the method of orthogona
l collocation using a MATLAB computer code. The effects of pollutant disper
sion in the gas phase, specific surface area available for mass transfer, t
hickness of the biofilm, and adsorptive capacity of the solid support on th
e biofilter performance were investigated in detail. The steady-state remov
al efficiency appears to be nearly independent of gas-phase dispersion of t
he pollutant in the normal industrial range of operations. Results also ind
icate that the biofilter performance is a strong function of specific surfa
ce area for mass transfer and biofilm thickness. Simulation results further
suggest that higher adsorptive support media are capable of handling load
fluctuations irrespective of the rate of reaction in the adsorbed phase.