Centralized deicing pads may be located near terminals and gates, along taxiways serving departure runways, or near the departure end of runways. An airport may use one or a combination of all of these locations for deicing/anti-icing. Road salt (i.e.,sodium chloride or potassium chloride) may be used to deice/anti-ice paved areas that are not used by aircraft (e.g.,automobile roadways and parking areas) but are not considered suitable for deicing/anti-icing taxiways, runways, aprons, and ramps because of their corrosive effects.
Most ADF is applied to aircraft through pressurized spraying systems, mounted either on trucks that move around an aircraft, or on large fixed boom devices located at a pad dedicated to deicing. Airlines typically purchase ADF in concentrated form (normalized) and dilute it with water prior to spraying.
Most of the aircraft deicing fluid is not designed to adhere to aircraft surfaces. Consequently the majority of ADF is available for discharge due to dripping, overspraying, tires rolling through or sprayed with fluid, and shearing during takeoff. Once the ADF has reached the ground, it will then mix with precipitation, as well as other chemicals found on airport pavements. These chemicals typically include aircraft fuel, lubricants and solvents, and metals from aircraft, ground support, and utility vehicles. Water containing these substances enters an airport’s storm drain system. At many airports, the storm drains discharge directly to waters of the United States with no treatment.
Runoff from deicing activity at airports is usually composed of water containing one to 40 percent ADF, grit, and sand. This ADF runoff is not directly dangerous to human health, but when it enters the environment, it can pollute bodies of water with increased organic burden, reducing the oxygen levels in the water. This kind of pollution is defined as COD or BOD (chemical or biological oxygen demand) and is closely regulated by EPA.
Runoff from the deicing treatment process can have the following negative environmental impacts on water quality:
• Contamination of drinking water sources, both on the surface and in groundwater;
• Red water in residential areas and parkland;
• Reductions in dissolved oxygen;
• Fish kills; and
• Reduced organism abundance and species diversity.
In order to reduce discharges of untreated ADF wastewater for the industry, EPA concluded that the best available technology would need to include two basic components. The first is a requirement to capture and collect a specified proportion (either 20 or 60 percent) of available ADF. The second component is a requirement to treat the collected ADF to meet specified end-of-pipe discharge limitations.
EPA recently developed regulations requiring large airports to collect and store spent ADF, treat it biologically or by distillation, and either dispose of it properly to a sewer system or recover it for reuse. The regulations include technology-based effluent standards for discharges from airport deicing operations.
Primary airports with 1,000 or more annual jet departures, and 10,000 or more total annual departures, would be required to collect the deicing fluid and treat the wastewater. Airlines typically select procedures for deicing/anti-icing their aircraft, which are then approved by the FAA.
The new regulations would impose a regulatory and financial burden on airports, requiring them to collect the runoff from the deicing procedures, store it, and either treat it onsite or send it to a waste treatment contractor.
Controlled Atmosphere Separation Technology
The two methods that have been approved for ADF treatment are biological methods and distillation:
• Biological systems use organisms, such as bacteria, which are selected to consume the pollutants and remove them from the effluent.
• Distillation is based on the evaporation of water from the effluent, capturing the vapor and condensing it into a cleaner liquid.
Controlled Atmosphere Separation Technology (CAST) is an advanced vacuum flash distillation system with significant advantages over other methods used, including the added financial benefit of recovering the ADF for reuse or resale.
The central component of the CAST systems is a distillation chamber (still), where heated effluent is sprayed through an atomizer into a low-pressure atmosphere, causing the water to evaporate from the effluent. The effluent becomes highly concentrated, and additional contaminants collect at the bottom of the still, and are removed from the concentrated effluent. The water vapor is collected at the top of the chamber and condensed into water of much higher purity.
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