De-icing of aircraft and runways
Aircraft are de-iced with propylene glycol, and runways are treated with potassium formate to prevent skidding. Potassium formate is a kind of salt and is used instead of urea today since its nitrogen concentration is much lower. Propylene glycol and potassium formate as such have low toxicity levels and break down easily in nature. But this breakdown requires a great deal of oxygen, so the compounds can cause oxygen depletion in waterways and groundwater if large quantities are released. In order to have as small an impact on the water around Arlanda as possible, a number of measures are carried out.
Glycol fluid is recycled after the aircraft’s de-icing
De-icing is only allowed in areas with a special glycol recovery system. As much glycol fluid as possible still on the ground once an aircraft has been de-iced is suctioned up by glycol recovery vehicles. Given its relatively high concentration of glycol, the fluid is recycled. The fluid collected is treated and concentrated into new, pure glycol at the Vilokan facility at Arlanda. Fluid with a relatively low glycol concentration not suctioned up runs into the glycol recovery system and is then soon pumped to the Käppala treatment facility.
Most chemical breakdown takes place in the airport’s treatment facility
Formate from runway anti-skid treatment and glycol that drips off taxiing aircraft end up in the surface water from the runways and aprons. Most of this is conveyed to surface water treatment facilities, where the chemicals are broken down using biological processes. This is done largely in the airport’s treatment facilities before the water is released into waterways.
Samples show improvements in the Märsta river
The water quality of the Märsta river has improved recently, in part as a result of Arlanda’s measures to reduce the impact on this waterway. The catchment area for the Märsta river includes the town of Märsta, a number of companies, farms and the airport, all of which have an impact on the waterway. The water quality of the Märsta river has improved over the last few decades, and in the latest assessment the river was classified as having “moderate ecological status” and “does not achieve good chemical surface water status” based on the assessment criteria of the EU Water Framework Directive.
200,000 square metres of membrane protect the groundwater around Runway 3
Runway 3 extends in part over a ridge of stratified sand and gravel that holds groundwater, so it is especially important that glycol and salt residues do not reach it. This was also a high priority when the runway was built. Runway water therefore runs down into drains along the runway and is then conveyed to a retention basin, where it is treated if necessary. A 1.5 millimetre thick water-impermeable membrane has been laid at a depth of 1–2 metres in the area around the ridge. This allows the water along the runway to be conveyed to the runway’s treatment system. A total of 200,000 square metres of membrane have been laid out around Runway 3, which is equivalent to the area covered by 28 football pitches.