De-icing of aircraft and runways
Aircraft are de-iced using propylene glycol, and when runways are de-iced, potassium formate is used. Potassium formate is a kind of salt and is used today instead of urea.
Propylene glycol and potassium formate as such have low levels of toxicity and break down easily. However, a lot of oxygen is needed in their decomposition, so the compounds could cause oxygen deprivation in watercourses and in the groundwater if large quantities are released. In order to minimise the impact on the water around Stockholm Arlanda, a number of measures are carried out.
Glycol is recovered after aircraft are de-iced
De-icing is only allowed on surfaces where a special drainage system for recovering glycol is installed. As much as possible of the glycol remaining on the ground once an aircraft has been de-iced is suctioned up by suction vehicles.
Because of the relatively high concentration of glycol, this fluid can be used for recycling or as an additional source of carbon in the local water treatment facility. The glycol fluid that is not suctioned up, which has a relatively low glycol level, runs into the glycol drainage system and is eventually pumped over to the Käppala water treatment facility.
Breakdown of chemicals takes place mostly in the airport’s treatment facility
Formate from de-icing and from glycol that drips off aircraft when they taxi out to a runway ends up in the surface water that runs off runways and aprons. Most surface water is conveyed to surface water treatment facilities, where the chemicals are broken down through biological processes. This breakdown is largely carried out in the airport’s water treatment facilities before the water is conveyed into watercourses.
Water samples show improvements in the Märsta River
The water quality of the Märsta River has improved in recent years, partly as a result of Stockholm Arlanda’s measures to reduce its impact on the watercourse. The catchment area of the Märsta River includes the town of Märsta, many companies, farms and the airport, which all have an impact on the watercourse.
In an inventory of the Märsta River taken in 1988, the water quality was rated “poor”, in part as a result of the urea and glycol used at Stockholm Arlanda, which contributed to oxygen deprivation in the river. The water quality has improved since then, and today the Märsta River has been classified as having “moderate ecological status” and “good chemical surface water status” according to the assessment criteria of the EU Water Directive. The objective is to achieve “good ecological status” by 2021.
The presence of the chemical PFOS at the airport
In a survey conducted in 2008, the presence of the chemical PFOS was identified, among other places, in Lake Halmsjön and the river Kättstabäcken. Since then, Swedavia has worked to increase knowledge about where PFOS is produced at the airport and how it spreads and acts. A pilot facility is operating in order to assess a treatment method.
Read more about PFOS.
Treated wastewater can be used as fertiliser
It is common for wastewater from operations such as vehicle washing facilities, workshops and aircraft hangars to contain elevated levels of metals and oil. At Stockholm Arlanda, there are a number of treatment facilities that remove these pollutants before the water is conveyed to the local treatment facility.
Treating wastewater is important since the sludge formed in the treatment facility contains valuable nutrients and can be used to some extent as fertiliser in fields.
200,000 square metres of membrane protects groundwater around Runway 3
Runway 3 extends in part over a boulder ridge that contains groundwater, so it is especially important that glycol and salt residues do not reach it, which was also a high priority when the runway was built. The water from the runway thus runs down into sewers along the sides of the runway and is then conveyed to an overflow area and treated if necessary.
A 1.5 millimetre water-impermeable membrane has been laid out in the area of the boulder ridge at a depth of 1-2 metres. This allows the water from the sides of the runway to flow into the runway’s sewage system. In all, some 200,000 square meters of membrane has been laid out by Runway 3, the equivalent of 28 football pitches.