Biofiltration of toluene vapor under steady-state and transient conditions: Theory and experimental results

Removal of toluene vapor from airstreams was studied in a vapor phase biological reactor known as a biofilter. The reactor was packed with a mixture of peal and perlite particles on which a mixed microbial population (consortium) was immobilized and formed a biolayer. The reactor was operated over a period of 11 months under various inlet-airstream toluene concentrations and flow rates of the contaminated airstream. Except at start-up, no supplemental nutrients were provided to the column, which remained active and never exhibited any significant pressure drop build-up. The process was modeled with general mass balance equations which take into account reaction, mass transfer, and adsorption of the pollutant onto the packing material. The model equations were solved numerically and the predicted concentration profiles agreed very well with the experimental data, for both steady-state and transient operation. Predicted concentration profiles for the biofilm indicate that toluene gets depleted before oxygen in a thin layer of the order of 35 μm. This finding is opposite to what has been reported for hydrophilic solvents where oxygen is depleted before the contaminant in the biolayer. The model equations have been used in parameter sensitivity studies that have revealed the parameters which need to be accurately known for predicting the performance of a biofilter.