Airports face a unique problem when dealing with stormwater containing glycol based de-icing fluid. Very high cBOD5 levels, due to glycol combined with flows that increase rapidly as the snow melts, result in a wastewater stream that is difficult to treat in a conventional suspended growth system. De-icing pads are designed to drain as quickly as possible, which can result in significant peaking factors in downstream treatment systems. CBOD5 concentrations in the resulting runoff can exceed 10,000 mg/l. The loading spikes and low water temperatures can cause upsets in treatment systems and can result in significant surcharges when discharging to a municipal wastewater treatment system or extensive environmental damage when discharged directly to a receiving stream.
Airports are extremely sensitive to the dangers presented by waterfowl and subsequent bird strike potential. While some airports operate pond systems for stormwater storage and/or treatment, the use of open surface water systems is typically discouraged. Treating the stormwater on-site typically requires a system with no exposed water surfaces to attract waterfowl, making storage or flow equalization lagoons impractical.
The vertical flow SAGR is the ideal solution for CBOD5 reduction when treating of airport stormwater contaminated with aircraft de-icing fluid. The SAGR is an attached growth system, maintaining biomass within the system between stormwater runoff events, while preventing any biomass washout during peak hourly flows. The biomass maintained within the system provides the ability to ramp up treatment very quickly, even with cold water temperatures. Because the SAGR is located mostly below grade and is fully covered with woodchips or mulch, no free water surfaces are available to attract waterfowl. Also, the system does not interfere with site-lines and glide slopes at the airport, making it suitable for location between runways.
SAGR treatment process can remove up to 98 % percent of cBOD5 in airport stormwater runoff contaminted with glycol in de-icing fluid, effectively handling peak loadings up to 10,000 mg/l cBOD5 with cold water temperatures without losing biomass.