The use of urea has been abandoned
Anti-skid agents used at airports are water soluble organic biodegradable substance compounds. While soil’s microorganisms decompose these compounds, they this process consumes oxygen. Up to the mid-90s, the main anti-skid agent was urea, which is a nitrogenous substance that causes surface waters to become eutrophic and increases the amount of nitrogenous compounds in groundwater. The use of urea has been abandoned almost completely due to its environmental impact. In 2000, Finavia published internal instructions forbidding the use of urea at the airports where it impacts groundwater.
Non-nitrogenous alternatives
Acetates and formates are non-nitrogenous substances that are also used in food and cosmetics industries. Soil bacteria decompose them to water (H2O) and carbon dioxide (CO2). The most notable negative impact of using acetates and formates is the oxygen consumption (0.2–0.7 g O2/1 gram) caused by biodegradation, which is still less than oxygen consumption caused by urea.
Water quality is monitored
Finavia monitors the quality of groundwater and surface waters at most of its airports. We monitor water quality independently and according to the permit conditions or as agreed with environmental authorities. Samples taken from wells, standpipes, outlet ditches of runoff waters and waterways located in the vicinity of airports are analysed for nitrogen compounds (ammonium, nitrate and nitrite), water acidity, chemical oxygen consumption, conductivity and oxygen content. The amount of nitrogen compounds in groundwater is still monitored because of former use of urea.
Aircraft anti- and de-icing
Owing to the cold and humid winter conditions is Finland, it is common that snow and ice gathers on the surface of the aircraft. For flight-security reasons, they must be removed, as they disrupt the performance and controllability of the aircraft. Moreover, pieces of ice separating from the aircraft surface may be ingested into the engine and cause a failure. De-icing treatment prevents snow from attaching to the aircraft surface and the formation of an ice layer on it during the take-off run and take-off. On cruising level, the humidity and air pressure are low, so the ice-formation is negligible. Aircrafts are equipped with electronic or mechanical de-icing mechanisms in case of ice-formation during the flight. The ground-forwarding companies are responsible for anti-icing and de-icing treatments of aircraft.
Glycol consumes oxygen
In Finland, propylene glycol based liquids are used for both de-and anti-icing. During the preparation, de-icing fluids are added 20–50% water and 1–2% additives. Propylene glycol (C3H6(OH)2) is a highly water soluble and quickly biodegradable substance also used widely is the cosmetics industry. Its greatest hazards are the depletion of oxygen in waters caused by its degradation and the unpleasant odour of the degradation products. Propylene glycol solution requires a relatively large amount of oxygen (0.8–1.2 g 02/ 1 gram of solution), depending on the consistency. In conditions, where the only little oxygen is dissolved in water, the degradation slows down.
Mitigating the impacts
There is currently no environmentally friendlier alternative for using propylene glycol. The environmental impacts caused by glycol can, however, be mitigated through improved working methods requiring less chemicals and through introducing alternative methods or recovering glycol-contaminated runoffs. The glycol-contaminated runoffs collected at Helsinki-Vantaa airport are processed by the municipal water treatment works. At other airports, glycol water is recovered using suction vehicles in the apron area. Water is recovered at Tampere-Pirkkala, Kuopio, Oulu and Jyväskylä airports. The water is stored in pools and later transferred to the municipal water treatment works. Recovered glycol water can be used in energy production in Imhoff tanks or in water treatment process as a source of carbon. Finavia is responsible for the recovery of glycol water.
Glycol fluids can also be recycled. A few airports abroad have adopted this practice and this possibility is being studied also at Helsinki Airport. The wider introduction of recycling glycol fluids has been hindered by the costs.
