Transport of hydrophobic pollutants through biofilms in biofilters

Abstract

Treatment of air pollutants in a biofilter requires that the compound be effectively transported from the gas phase to the organisms that reside in a biofilm that forms upon a packing material. It has been suggested that biofilms have different transport properties than water making hydrophobic pollutants have higher removal rates than predicted based on water's transport properties. The objectives of this study were to experimentally determine partition and diffusion coefficients of a model hydrophobic compound ( α-pinene) through natural and artificial biofilms and to relate these to biofilm characteristics such as solids content and the substrate (VOC) being consumed during biofilm generation. This was done by setting up bench-scale biofilters to generate biofilm to use in partitioning and transport experiments. Batch partitioning experiments were conducted that indicated that α-pinene has a higher degree of partitioning into biofilm than into water due to the presence of solids (two orders of magnitude). A diffusion cell has also been designed and built to study the partitioning from air and diffusion of α-pinene through various artificial biofilms. The average diffusion coefficient of α-pinene through agar, which has the same partitioning properties as water, was found to be 3.4×10 −6 cm 2/ s (S.D.: 1.2×10 −6 cm 2/ s, n=12 ). Diffusion cell experiments performed with α-pinene using inactivated biofilm, previously grown on methanol and α-pinene, immobilized in agar indicate that initially sorption takes place within the film but after this initial lag phase, the transport rate is not significantly different from agar indicating the ratio of the diffusion and partition coefficient of the mobile phase is the same. Therefore, at steady state we expect the transport rates of hydrophobic pollutants through biofilms to be the same as through water.