SUB-SURFACE FLOW WETLANDS TO TREAT GLYCOL-CONTAMINATED STORMWATER FROM AIRCRAFT DE-ICING OPERATIONS, BATEA

Airports use glycol-based aircraft de-icing fluids (ADFs) for removing ice and snow from aircraft surfaces during winter and under frost conditions. Some relatively concentrated, spent ADF (Concentrate) may be collected from beneath aircraft for recycle or disposal at a local wastewater treatment plant (WWTP), but a significant part of the ADF at every airport will end up in sewers and ditches, be blown by jet or prop wash onto areas adjacent to de-icing pads, drip off onto aprons and runways during aircraft movement, or be collected with removed snow and ice. There are various on-site and off-site methods available to treat glycol-contaminated airport runoff, and one that is attracting increasing interest is the use of constructed wetlands (CWs) for treatment. Because the attraction of waterfowl is not desirable at airports, CWs considered for them are usually of the subsurface flow (SSF) variety in which there is no open water and where the runoffs being treated flow under the normally dry surfaces of beds of gravel in which wetland plants are growing.This paper reviews two airport projects for the treatment of glycol-contaminated stormwater runoff in SSF CWs, one that has resulted in a large operating SSF CW, that at Edmonton International Airport (EIA), and one for an advanced form of CW, an engineered wetland (EW), which is now under construction, that at Buffalo Niagara International Airport (BNIA). (Engineered wetlands are semi-passive kinds of CWs in which process conditions are more actively manipulated and controlled.) For both projects, preliminary off-site, pilot-scale wetlands treatability testing was carried out to define feasibility and determine kinetic and other parameters needed to proceed with the design of full-scale facilities. This paper also reviews the treatability test results, overviews the design of the full-scale facilities, and demonstrates that the use of SSF wetlands to treat glycol-contaminated stormwater runoff at northern airports is Best Available Technology, Economically Available (BATEA).One cubic metre, indoor, aerated and un-aerated CW and EW test cells at an off-site central pilot test unit were used for both treatability tests. For the EIA treatability test where an ethylene glycol (EG) based ADF is used for aircraft de-icing, a synthetic stormwater (SW) indicative of worse case spring melt runoff conditions was prepared as the pilot unit feedstock, and the test cell were operated in a horizontal SSF (HSSF) mode. For the BNIA treatability test, imported stormwater from the airport was spiked into vertical SSF (VSSF) cells with varying amounts of the propylene glycol (PG)-based ADF used there. Results were evaluated for the degradation of cBOD and other parameters.For the EIA treatability test in 1998, two HSSF EW cells were connected in series and an artificial stormwater indicative of worse case conditions was used as the pilot unit feedstock. In an-aerated tests, BOD removals of 50–60% were achieved at volumetric PFR removal rates of 0.2/d. For runs where the EW cells were aerated, rates increased 17 fold to 2.35/d.For the BNIA treatability test in 2006 with PG-contaminated stormwater, aeration also was found to profoundly affect treatment performance. When aerated at 0.85 m3 air per hour (per m3 of wetland bed), the volumetric (2TIS) cBOD5 removal rate constant averaged 7.7 d−1 with a temperature coefficient () of 1.03, based on experiments conducted at 22°C and 8°C.