Biodegradation of De-icing Com- Pounds in Columns Simulating a Range of Natural Conditions

The determination of the fate of aircraft de-icing fluids in near runway soils is important in evaluating environmental impacts and in the design of treatment system. The effect of biodegradation of the primary component of de-icing fluids, propylene glycol (PG), was tested in waters-saturated sand columns. Biogrowth significantly reduced the hydraulic conductivity of the sand. This change in hydraulic conductivity affects both the flow of water and the rate of migration of dissolved chemicals in the flowing water. With intermittent loading averaging 43 mg PG/d, hydraulic shear and endogenous biomass decay balanced bacterial growth. A lower final conductivity occurred at a lower flow rate, but increased loading (by two to four times) did not lower the final conductivity. After significant sand plugging by the bacteria grown on PG, periods of five to eight days when PG was not present resulted in significant partial recovery of the original conductivity. A trend of decreasing hydraulic conductivity with increasing biomass was observed. The results are important to consider when determining the fate of de-icing compounds in near runway soils and in the design of biofilters for treatment. ABSTRACT