Innovative Treatment of Recovered Aircraft Deicing Fluids.

Cold weather application of aircraft and pavement deicer fluids (collectively referred to as deicers) at the Spokane International Airport (SIA) result in discharges of stormwater commingled with deicers to a stormwater infiltration/evaporation area.  The predominantly propylene glycol deicers readily decompose to cause chemically reducing conditions in the groundwater beneath the site.  These reducing conditions mobilize small amounts of naturally occurring arsenic and iron into the groundwater. SIA has implemented use of glycol recovery vehicles (GRV) to control the amount of deicers in stormwater and improve groundwater quality. At issue is the appropriate means to treat and dispose of the recovered deicer. An evaluation of options including conventional wastewater treatment, recovery and reuse, and land treatment, indicated that controlled application to land for treatment by soil micro-organisms is the most viable short-term alternative.  Biological degradation of propylene glycol deicer by soil microbes has been demonstrated in research (Bausmith and Neufeld, 1999; Castro et al., 2000).  These studies showed that, within proper conditions, propylene glycol and other compounds in the deicers were readily treated by soil and crops.  The limiting design parameter is the chemical oxygen demand (COD) of the recovered deicer.  The local soil capacity for daily COD loading ranges from 117 to 611 lb/ac-day depending on the month (April –October).  The recovered deicer can be applied at 150 to 1,050 lb COD/ac in any one application with appropriate rest periods between applications  The challenge was the method of application which involved application rates greater than typical agricultural sprayer and far less than typical irrigation. Monitoring data from the land treatment operations for the past four years indicates successful treatment of more than 100,000 gallons of recovered deicer each year.