Transport and degradation of hydrophobic pollutants in biofilms in biofilters

This research focuses on understanding the transport and reaction mechanisms taking place in biofilms in biofilters treating hydrophobic pollutants. The objectives of this study were to experimentally determine partition and diffusion coefficients of a model hydrophobic compound (alpha-pinene) through natural and artificial biofilms. This was done by setting up bench-scale biofilters to generate biofilms to use in partitioning and transport experiments. Batch partitioning experiments indicate that alpha-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 transport of alpha-pinene through various artificial biofilms. The average diffusion coefficient of alpha-pinene through agar, which has the same partitioning properties' as water, was found to be 3.4 x 10 -6 cm2/s (S.D.: 1.2 x 10-6 cm2/s, n = 12). Transport experiments performed with alpha-pinene using inactivated biofilm, previously grown on methanol and alpha-pinene, immobilised in agarose 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.; A new explanation of high degradation rates was put forth whereby a biologically mediated transformation is taking place with alpha-pinene being oxidised into a more soluble compound. A simple model based on zero-order kinetics was developed that fit results seen in the diffusion cell using active a-pinene leachate immobilised in low melting point agarose. The proposed identity of this more soluble by-product, is cis-2,8-p-menthadien-1-ol, a menthadienol, a novel metabolite of alpha-pinene degradation. By extension, this model fits biofiltration data collected from Raschig ring biofilters treating alpha-pinene.