Large deicing pads were planned and built at Denver International Airport (DEN) for quick and efficient aircraft deicing near the departure runway thresholds. The pads are the cornerstone of a cold-weather management system that minimizes aircraft deicing at the gates, allowing gates to be more quickly available for inbound aircraft and minimizing interference with other gate operations, such as the loading of bags and food.
By concentrating the area in which full aircraft deicing is performed, the pads capture a more concentrated mixture of the spent glycol-based deicing fluid, allowing the captured fluid to gravity-flow to an onsite recycling plant, and minimize the amount of gate-applied deicing fluid that cannot be recycled economically because the fluid has mixed with precipitation from a much larger collection area, thereby diluting the glycol concentration. Diluted fluid (less than 1 percent glycol) must be sent to an offsite wastewater treatment facility.
In 2009, the recycling operation generated a cost savings of $1.4 million to DEN and resultant airline fees over the fees for disposal at the municipal sewage treatment plant, the Metro Wastewater Reclamation District (Metro). The combination of facility planning and operational improvements has steadily increased the amount of glycol captured and treated.
During the 2009-2010 deicing season, 71 percent of aircraft deicing fluid sprayed was collected, and 72 percent of the collected aircraft deicing fluid was recycled — 11 percent higher than the Environmental Protection Agency’s (EPA) proposed new rules, issued in August 2009, for Effluent Limitation Guidelines and New Source Performance Standards for the Airport Deicing Category.
Current FAA regulations in Parts 121, 125, and 135 prohibit a takeoff when frost, ice, or snow is adhering to the wings, control surfaces, or propellers of an airplane. DEN has strict and comprehensive Part 190 Aircraft Deicing Regulations, which provide a description of the aircraft deicing system and regulations, procedures, etc. The regulations are coordinated with the airport’s Stormwater Management Plan and ISO 14001-certified Environmental Management System.
Recycling — A sustainable strategy
DEN has substantial infrastructure in place to protect stormwater quality and maintain the separation of clean stormwater runoff from deicing waste (DIW) stormwater runoff. The major structural stormwater pollution control measures at the airport include the DIW stormwater collection/retention system, the West Airfield Diversion System (WADS), dedicated aircraft de-icing pads and an aircraft deicing fluid (ADF) recycling plant, secondary containment structures, oil/water separators within the clean stormwater system, and contained material storage and handling areas.
The airport operates four primary de-icing pads west of concourses A, B, C, and J, and a fifth pad on the west, known as WA, all strategically located enroute to the departure thresholds. Five to six aircraft can be deiced concurrently at each pad, for a total of 28 positions at one time.
Inland Technologies International Limited of Nova Scotia, Canada, began providing turnkey glycol services at DEN in 2004 with a full-time, 12-person team. Inland specializes in the design, development, and operation of petroleum waste treatment and airport glycol recycling services.
ADF TYPE, STORAGE, AND SUPPLY
Type I ADF (89 percent propylene glycol) and Type IV ADF (50 percent propylene glycol) are used for aircraft deicing. Type I ADF requires additives that improve the spray’s performance but can harm the environment. Glycol is biodegradable, but will generate high biochemical oxygen demand (BOD) during the decomposition process, which can severely deplete oxygen levels in waterways, choking off aquatic plants and animals.