In early nineties, Dutch scientist Arnold Mulder discovered, that one of his anaerobic microbial cultures kept removing nitrogen in an unexpected way. Mulder called this process “anaerobic oxidation of ammonium”, or anammox. It is a microbial process, in which anammox bacteria (or archaea) convert ammonia (NH3) and nitrite (NO2-) to dinitrogen gas (N2), thus gaining energy.
Over subsequent two decades, anammox became widely applied for the removal of nitrogen from reject waters from anaerobic digestion (ammonium-rich liquid fraction of anaerobically treated activated sludge). First applications of anammox went to sewage treatment plants receiving wasted activated sludge from adjacent plants, or nitrogen-rich industrial effl uents, and sewage treatment plants with insuffi cient capacity of tanks for nitrifi cation-denitrifi cation. These plants discharge more nitrogen than allowed by the municipal authorities, and face nasty sanctions. Unless plant operators persuade the authorities to elevate their nitrogen limits, one ofthe ways out is to remove part of total nitrogenous load from reject water via anammox. In addition to such cases, anammox is also applied at sewage treatment plants, where operators
are pushed to reduce their treatment costs.
In case of treatment plant in Ingolstadt (Germany), removalof one kilo of nitrogen from reject water via nitrifi cation- denitrifi cation consumes 4 kWh, while anammox consumes 0.8-2 kWh e.g. in Potsdam (Germany) it consumes 1,6 kWh.
Because “anammox” is patented trademark, suppliers call thisprocess “deammonifi cation”. To date, more than 100 sewage treatment plants are equipped with anammox, most of them situated in western Europe, north America and China. Theprice of anammox technology depends on the availability of unoccupied tanks on site, the level of automation, and quality of materials and technology. Anammox also saves organic
carbon and thus more methane can be produced from anaerobicallydigested sewage sludge.
Municipalities are waking up to the possibilities to reducetheir wastewater treatment bill. Due to the extensive full- scale experience and several different providers, savings provided by anammox are considered to be among the “lowest hanging fruit”.