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Municipal Case Studies

Geneva - Switzerland

Meeting the demands of rapid expansion


4 high-speed physical-chemical clarifiers
Flexible operation : dry weather flow 3.2 m3/s, full flow to treatment 6 m3/s

Biological degradation of urban and industrial fats in an aerated tank
Ease of operation

Compactness: pollution degradation and filtration in the same cell
Periodic backwashing of the filter
Media used for biomass growth : Biostyrene™, polystyrene beads

Built in 1967, Geneva-Aïre treatment plant was commissioned to meet the wastewater demands of an increase in population.
The plant had to treat mixed effluents from the Geneva conurbation (from homes, industries, small businesses and tourist locations) and also wastewater from neighbouring districts in France.
By 1980 the plant became overloaded, the water of the Rhone was deteriorating.
Many local residents were affected by unpleasant odours and the plant's operating and maintenance difficulties were increasing.

To meet new discharge standards and the additional load from anticipated development of the area up to 2010, the capacity of the new Geneva-Aïre 2 plant has been doubled and will be capable of treating up to 600,000 PE. The treatment works has been equipped with new compact technologies that are both environmentally friendly and compatible with economic constraints.

The Solution

Veolia Water Technologies was responsible for the design, procurement, installation and commissioning of the processes associated with the water treatment system.

Constructed on the original site, with limited space available, the new plant accommodates the latest compact and innovative technology including Actiflo lamella settling with ballasted floc and Biostyr, biofilters. The most stringent nitrogen and phosphorus discharge standards are adhered to under all operating conditions. This high quality effluent is then discharged into the River Rhone

Technical Details

Wastewater Treatment:

Pre-treatment of collected wastewater :

  • 15-mm screening
  • grit and greases removal
  • 3-mm screening

Grease and oil are treated separately using the Biolix process.

Primary treatment :

Elimination of suspended solids by coagulation/flocculation stage with the addition of microsand, followed by lamellar settling of ballasted flocs

Secondary treatment :

Elimination of carbonaceous pollution and nitrification of nitrogenous pollution by biological stage in aerated biofilters

Sludge Treatment

  • Thickening of the primary and biological sludge from the Actiflo hydrocyclones is carried out by 3 lamella thickeners. The sludge receives additional dewatering by passing through a gravity belt thickener resulting in a dry solids content of 7%.
  • Anaerobic digestion of the thickened sludge results in the production of biogas which is used as a fuel for the hot water boilers.
  • Dewatering by centrifugal separation produces sludge with a dry solids content of 30%.
  • Drying: Utilisation of the biogas produced at the anaerobic digestion stage ensures an autothermic drying stage.

Finally, the dried sludge granules (95% dry solids) are stored before being incinerated with urban waste at another location.

Air Treatment

The wastewater and sludge treatment facilities have been designed to contain odour with process units covered or located inside buildings.
The polluted air, from this totally enclosed environment is extracted and treated by a chemical odour removal plant.

Veolia Water Technologies' Processes

Geneva Processes

Biolix, Actiflo, Biostyr