Nitrogen removal

Many sectors produce highly polluted wastewater, with nitrogen being one of the main pollutants. Removing nitrogen can be very expense.

NAS®, the innovative anammox technology developed by Colsen, is an energy-efficient wastewater treatment method based on anammox bacteria. This technology helps save costs and is used for industrial and municipal wastewater treatment plants.


Our robust NAS® anammox technology lowers the operating costs of conventional water treatment methods by cutting energy consumption and sludge disposal costs. NAS® systems are equipped with a clarifier or MBR (Membrane Biological Reactor) but can be fully configured to the customer’s needs & wishes.

If you work in the municipal sector, you can use NAS®-ONE technology. This technique is suitable for sidestream treatment after mesophilic or thermophilic sludge digestion, with or without TPH (Thermophilic Pressure Hydrolysis) pre-treatment. NAS®-ONE technology is a highly efficient wastewater treatment method based on high-load anammox bacteria that removes high levels of nitrogen from sludge filtrate, even at high organic and solid concentrations.

Pizzoli NAS
Waterschap Vechtstromen Hengelo NAS ONE
Isolux Salamanca
LVM Oosterbierum


Anammox micro-organisms allow for efficient nitrogen removal by short-cutting the conventional nitrogen cycle. These bacteria are autotrophic, which means they do not need any organic pollution to work as intended. They use ammonium and nitrite as substrates and work most optimal at mesophilic temperatures (35-37°C) in the absence of oxygen. All NAS® technologies are equipped with our proprietary aeration control, which ensures that part of the ammonium is converted to nitrite. Depending on the NAS® application in question, the aeration phase is carried out in the same tank or a separate one.


Low energy consumption, reduced sludge production and the absence of a carbon source mean that NAS® systems can help you cut water treatment operating costs by 40%!

Would you like to know more?
Ask Robin

Robin Jordaens , Business Development Manager