Sidestream-based Nitrogen Removal System


Sidestreams such as digester supernatants, centrates and filtrates have extremely high nitrogen concentration, which is typically recycled to the head of the plant. This often leads to system upsets or significantly increased treatment volume and energy consumption, as well as carbon source consumption for denitrification.

AnammoPAQ is an innovative sidestream treatment technology that utilises the power of the Anammox® bacteria to treat high nitrogen concentration sidestreams in a compact, energy efficient reactor. The system optimises plant energy and operating and maintenance expenditure, while minimising footprint.

The AnammoPAQ process is an elegant shortcut in the natural nitrogen cycle. The process utilises Anammox bacteria which directly converts ammonium (NH4+) and nitrite (NO2) into nitrogen gas.

The complete granular sludge nature of the AnammoPAQ process allows for superior loading rates application, thereby significantly reducing process footprint and energy demand. This is turn, further optimises nutrient management and reduces overall plant operating and maintenance costs and footprint.

Since the first full-scale plant commenced operations in 2002, more than 60 full-scale systems have been installed globally and are running successfully. Key features and benefits of the AnammoPAQ system includes:

  • Compact footprint due to high loading rates
  • Low project costs
  • Low operating and maintenance costs
  • Significantly lower energy costs for ammonia removal
  • Stable and robust process
  • High experience and large reference base
  • Quick startup

AnammoPAQ technology is a continuous flow system in which nitritation and anammox conversion occur simultaneously in a single process unit. Anammox (anaerobic ammonium oxidation) conversion is an elegant short-cut in the natural nitrogen cycle where ammonium and nitrite are converted directly to nitrogen gas. Since the Anammox process involves removal of ammonium over nitrite (NO2) rather than nitrate (NO3), 63 percent less oxygen (O2) is required, while eliminating the need for an external carbon source altogether, and reducing overall sludge production. Optimal process control ensures retention of AOBs and Anammox bacteria while eliminating NOBs, leading to stable and robust operation.

  1. Ammonia-rich influent
  2. Aerators for mixing and ammonia removal process
  3. AnammoPAQ separator for biomass retention
  4. Effluent exits the reactor

The process stoichiometry is detailed below:

NH4+ + 1½ O2 à NO2 + H2O + 2H+

NH4+ + NO2 à N2 + 2H2O



ANAMMOX® is a registered trademark of Paques BV