Nereda design capacity

  • 20000 m3/d
    Dry Weather Flow
  • 2880 m3/h
    Peak Flow
  • 95000 PE
    PE (PE = 60 gBOD/d)

Project facts

  • Client
  • Licensee
  • Location
    Kloten, Opfikon, Switzerland
  • Period
  • Wastewater
  • Project type
  • Process configuration
    Pre-treatment + Primary settler + Nereda + Ozonation + Sand filtration

About Kloten Nereda® WWTP - Switzerland

Kloten-Opfikon Wastewater Treatment Plant (WWTP) is situated in the district of Bülach, in the canton (district) of Zurich. It is located in the north of Switzerland, about 10 km north of the city of Zurich.

The challenge

The existing plant at Kloten treated wastewater for 65,000 people. Given the increasing population and more stringent effluent requirement, an upgrade to 95,000 p.e. was needed. The Nereda anaerobic technology method was trialled by operator Abwasserreinigung Kloten Opfikon (AKO) at Kloten-Opfikon WWTP, from June 2014 to April 2015 for 11 months, on a pilot scheme running under real conditions.

The solution

The trial was carried out by Nereda’s developers, Royal HaskoningDHV, and WABAG Wassertechnik AG. The aim of the pilot was to demonstrate Nereda’s effectiveness at treating typical Swiss wastewater under different temperature conditions during two phases. For Phase one (June to October 2014), the plant was operated with a constant inflow, while Phase two (November 2014 to April 2015), with the aim of assessing cleaning performance during the winter months with cold wastewater. The trial plant was housed in a shipping container, with a reactor capacity of approximately 1.5 m³ volume at a water level of about six meters. After a successful trial period, Nereda technology was selected for the upgrade of the wastewater treatments plant. Nereda technology can be retrofitted in an existing installation, almost doubling the facility’s capacity within the same volume, which makes it an attractive solution for existing sites with limited area.

The outcome

The new Nereda installation at Kloten is based on a four-tank configuration. Construction began in 2019, with start-up planned in stages between 2021 and 2024. This is the second Nereda site by WABAG Wassertechnik AG in Switzerland, following the successful installation at Alpnach.

Claudio Lehmann, process engineer of WABAG Switzerland, confirmed Nereda’s suitability for Kloten: “Its consistent performance confirmed that the Nereda technology is an excellent option for application at full scale, in terms of nutrient (ammonium, nitrogen, phosphorus) and solids removal. Moreover, Nereda could be retrofitted in the existing installation, which made it even more attractive to select the Nereda technology”.


  • Retro-fitted technology

  • Excellent performance at low temperatures

  • Increased capacity 

  • Minimal site footprint 

  • Environmentally friendly solution