The ANAMMOX® (anaerobic ammonium oxidation) process is an innovative biological process that represents a major breakthrough in nitrogen removal. It is a cost effective, robust and sustainable way of removing ammonium from wastewater and from waste gas. Compared to conventional nitrifation/denitrification, operational costs are reduced by up to 90% as are CO2 emission levels. This brings the plant’s carbon footprint down to a minimum.

The ANAMMOX® conversion is an elegant shortcut in the natural nitrogen cycle. In combination with nitrification ANAMMOX® bacteria convert ammonium (NH4+) directly into dinitrogen gas. Working closely with Delft University of Technology, Paques developed the patented ANAMMOX® process for commercial purposes.

Global presence

ANAMMOX - ammonia removal by Paques

The first full-scale ANAMMOX® plant started up in the Netherlands in 2002. Ten years later there are more than 20 full-scale ANAMMOX® references. Paques’ experience of over twenty years in the design, construction and operation of biological wastewater treatment plants has resulted in an ANAMMOX® reactor that combines excellent biomass retention and granule formation with very good mixing. Effective conversion and stable operation are therefore guaranteed.

Advantages of ANAMMOX® compared to conventional nitrification/denitrification

  • High nitrogen removal
  • No methanol dosing is needed for denitrification
  • Up to 60% reduction of power consumption
  • Minimal production of excess sludge
  • Up to 90% reduction of CO2 emission
  • Up to 50% less space required


The ANAMMOX® process can be used for the removal of ammonium from all types of effluents with a relatively high ammonium concentration (NH4+-N > 100 mg/l).

Some examples of processes and industries where these effluents can be found

  • Municipal wastewater treatment (reject water from a sludge digester)
  • Organic solid waste treatment (landfills, composting, digestion)
  • Food industry
  • Manure processing industry
  • Fertilizer industry
  • (Petro)chemical industry
  • Metal and Mining industry

Working principle

In the ANAMMOX® reactor ammonium is converted to nitrogen gas. The reaction is executed by two different bacteria, which coexist in the reactor. Nitritation bacteria oxidize about half of the ammonium to nitrite. Anammox bacteria convert the ammonium and nitrite into nitrogen gas.

The ANAMMOX® reactor is aerated and equipped with a biomass retention system. The reactor contains granular biomass. The wastewater is continuously fed to the reactor. The aeration provides for rapid mixing of the influent with the reactor content, intense contact with the biomass and oxygen supply to drive the conversion.

The treated wastewater leaves the reactor by passing the biomass retention system at the top of the reactor. The granular biomass is separated from the cleaned wastewater, assuring high biomass content in the reactor. Together with the dense conversion properties typical for granular biomass, the high biomass content provides for high conversion rates and therefore a small reactor volume.

ANAMMOX® cases