Aircraft are de-iced with propylene glycol, and potassium formiate is used to prevent skidding on runways. Potassium formiate is a kind of salt and is used today instead of urea.
Propylene glycol and potassium formiate in themselves have low toxicity and are easily biodegradable in nature. But they require a lot of oxygen to degrade and may thus cause oxygen deficiency in waterways and groundwater if large quantities are released. To ensure that waterways and groundwater around the airport will be affected as little as possible, the airport carries out a number of measures.
De-icing of aircraft and anti-skid treatment
De-icing is only allowed on surfaces where there is a special piping system for collecting glycol. As much as possible of the glycol fluid remaining on the ground once an aircraft has been de-iced is suctioned up by suction vehicles. This fluid may be used for recycling or as an additional carbon source in municipal water treatment units, given the relatively high concentration of glycol. The glycol fluid that is not suctioned up runs down into the piping system for glycol. This fluid has a relatively low concentration of glycol and is eventually pumped to a municipal water treatment unit.
Formiate from de-icing runways and glycol that drips from the aircraft while taxiing end up in the surface water from runways and aprons. Surface water from Runway 1 is processed in a local treatment unit where both formiate and glycol are degraded before the water is released into nature. The airport also plans to build water treatment units for all runway systems.
200,000 square metres of membranes protect the groundwater at Runway 3
Part of Runway 3 is located above a boulder ridge containing groundwater. It is thus extra important to prevent glycol and formiate salt residue from reaching this groundwater, and this was also a high priority during the construction of the runway. Water from the runway thus runs down into wells along the edges and is then piped to a retaining reservoir and treated as necessary.
In the boulder ridge area, a 1.5 mm thick water-tight membrane has also been laid out at a depth of 1-2 metres. This causes water from the side of the runway to flow into the runway piping system. A total of 200,000 square metres of membrane have been laid out around Runway 3, equivalent in area to 28 European football pitches.
Three water treatment units at Stockholm Arlanda
Water that comes from vehicle washing facilities at the airport often contains metals. At Stockholm Arlanda Airport there are three water treatment units that remove these metals before the water is piped to a municipal wastewater treatment plant. The sludge formed at the municipal wastewater treatment plant can then be used as an agricultural fertiliser. Run-off from the airport also flows − via a water treatment unit − into two creeks, Halmsjöbäcken and Kättstabäcken, which join just south of the airport to form a river, Märstaån, which passes through the community of Märsta before emptying into a bay called Steningeviken in Lake Mälaren.
Samples indicate improved waterways
In 1988 the status of the waterways around the airports was “poor”. Thanks to a number of different measures, the 2008 survey indicated that the ecological status had improved in every waterway and was considered to be “moderately good”. In another survey carried out in 2008, the chemical PFOS was found to be present in the sediment of Lake Halmsjön and elsewhere.