The Impact of Biodegradation of De-icing Chemicals on the Con- Ductivity and Dispersivity of Porous Media

Environmental contamination with aircraft de-icing fluids (ADF) is becoming a concern. Propylene glycol (PG) composes the largest fraction of the ADF most commonly in use in the U.S. The biodegradation of PG and ADF in saturated and unsaturated sand columns was evaluated, in addition to the impact of biodegradation on the hydrodynamic characteristics of the porous media. In studies with unsaturated sand, the amount of PG removed increased with spilled concentration (from 1000 to 300,000 mg/L), but decreased as multiple pore volumes were spilled. Tests in saturated columns were conducted at average loadings of ADF or PG of 43 to 32,000 mg/d. The hydraulic conductivity of the sand was reduced due to biogrowth, but to a lesser extent with increasing PG or ADF loadings above 110 mg/d. At higher groundwater flow rates, there was less biomass accumulation in the sand and therefore less decrease in hydraulic conductivity. Dispersivity increased over time as bacteria grew in the sand. Understanding the effects of bacterial growth in sand on the hydrodynamic properties of the media and the net biokinetics of the system will aid in predicting the fate of de-icing compounds in the natural environment and engineered treatment biofilters. therefore be released into the environment at very high concentrations (on the order of 1,000 to 500,000 mg/L). Although PG is readily degradable by many bacteria that are commonly present in soil, the high loading may overwhelm the ability of the natural bacteria to fully degrade the PG before it reaches the groundwater (where it has been detected as reported by Cancilla et al., 1998) or other surface water bodies. If PG enters streams at even fairly low concentrations (10 to 100 mg/L), the dissolved oxygen could be completely consumed by aquatic microorganisms, which would negatively impact fish and other aquatic life. Another problem associated with ADF is the toxicity of the surfactants and corrosion inhibitors to fish, water fleas, and microorganisms (Cornell and Hernandez, 1998 WEF). Therefore, it is