Water

The careful use of water and the treatment of wastewater is a given for the Zurich Airport Group.

Relevance

Clean water is a precious resource which Zurich Airport Ltd. is committed to conserving at all its airports. Along with minimising the volume of fresh water consumed, the company ensures wastewater is appropriately treated to keep watercourses clean. Various types of wastewater are produced at airports, each of which must be treated in different ways. These include domestic wastewater, aircraft sewage and wastewater from workshops, as well as runoff from operational areas and from aircraft de-icing.

Approach

Fresh water

Zurich Airport obtains drinking water from the municipal water supply for the town of Kloten. It also pumps groundwater itself. This is because some parts of the infrastructure are located below ground and are at risk if the groundwater table rises above a critical level. The pumped groundwater is used as process water and for toilet flushing. Rainwater collected from roofs is also used to flush some toilets, which additionally helps to control rainwater runoff. Due to construction work at the main airport complex, it was not possible to obtain groundwater as usual in the reporting year. For this reason, more drinking water had to be fed into the system.

The airports of the Zurich Airport Group in Latin America likewise obtain their drinking water from the public water supply and are constantly taking steps to reduce their demand for fresh water. Under the name “Aqua Project”, various measures at the airports in Brazil have been combined with the three strategic focuses of treating used water, reducing demand and accurately measuring consumption. In the reporting year, for example, measures were implemented to collect the condensation from stationary air conditioning systems for aircraft at Vitória Airport, thereby making it accessible for further use as grey water.

Noida Airport in India plans to meet 80% of its fresh water needs with treated rainwater. As Noida lies in a tropical zone with heavy seasonal precipitation, rainwater will be stored in tanks for use later in the year.

Wastewater

Like the municipalities in the canton, Zurich Airport has its own general drainage plan (GEP) which sets out the basic principles for water protection on the airfield. Following the “prevent – separate – treat” approach, the aim is to produce as little wastewater as possible. Along with measures to ensure that airfield drainage systems meet regulations, the drainage plan includes stipulations relating to the operation and maintenance of the existing sewage and pump systems.

In accordance with the drainage plan, the wastewater produced at Zurich Airport is separated and suitably treated. All domestic wastewater, from toilets or restaurant kitchens for example, is discharged into the local sewage treatment plant (STP) at Kloten-Opfikon where it is treated. The contents of grease separators are sent to a biogas plant. Special wastewater, from workshops or from aircraft toilets for example, requires pre-treatment before likewise being sent on to the sewage plant.

Over the past seven years, the STP itself has undergone a process of ongoing modernisation and expansion while remaining in operation. The treatment of wastewater using a novel biological process allows conventional treatment stages to be replaced while consuming less energy and space.

The airports in Latin America all have their own STPs from which the treated water is directly discharged into watercourses or, as in Florianópolis in Brazil and Antofagasta in Chile, used locally for irrigation purposes. An STP is also planned for Noida in India in order to produce grey water that can be used for cooling and irrigation purposes, for instance.

Aircraft and surface de-icing

To ensure safe flight operations, both the aircraft and the operating areas at Zurich Airport must be kept free of ice in winter.

The winter of 2023/2024 was characterised by exceptionally high quantities of precipitation. Temperatures were well above the norm, which meant that only an average amount of snow fell. Due to the frequent precipitation events, demand for aircraft de-icing agents was nonetheless higher than usual. The position was different for surface de-icing agents, as the quantity used was within the long-term average. Aircraft are de-iced with propylene glycol, while formates are used for runway de-icing. Conventional road salt is used on roads, in multi-storey car parks and in the maintenance workshop.

Wastewater runoff from operational areas contaminated with de-icing agents is collected and treated in one of three ways depending on the degree of contamination (more information can be found online at Zurich Airport De-Icing Wastewater). One unique feature of treatment is the spraying of medium-contaminated wastewater over suitable green areas. As the water percolates down through the soil, the carbon compounds from the propylene glycol and the formate biodegrade, thus cleaning the wastewater in the process. To make even better use of the existing spray irrigation areas, further optimisation measures were implemented last winter.

To assess the success of the system, the degree of treatment is calculated for each winter season. This indicates what percentage of carbon contained in the collected wastewater was removed. In winter 2023/2024 the treatment level was 90% (previous year: 96%). The effective amount of carbon that was washed away untreated was therefore comparatively high, amounting to 34 tonnes. As the system’s catchment areas are primarily designed for aircraft de-icing, but more surface de-icing agent was discharged, proportionally speaking, this had a negative impact on the degree of treatment. Another reason for the low level of treatment is the high consumption of de-icing agents for aircraft during periods of rainfall, as far more de-icing agent drips onto runways and taxiways.

Key data

Fresh water consumption

Consumption of de-icing agents