Nitrogen containing compounds, primarily ammonia, are a serious water pollutant, which governments have begun regulating more strictly. Combined with increasing population pressures, the need for an efficient method for removing nitrogen from sewage is growing. Nature's own nitrogen cycle employs specialized bacteria to convert ammonia to nitrites and nitrates. Different bacteria then convert these products into inert, atmospheric nitrogen gas. Waste treatment plants employ these same bacteria to perform “biological nitrogen removal” (BNR).
Conventional BNR is achieved by complete oxidation of ammonia to nitrate (nitrification) followed by the reduction of nitrate to dinitrogen gas (denitrification). The typical removal of ammonia involves its oxidation by nitrifying bacteria into nitrite (NO2−), which is then further oxidized into nitrate (NO32−). The result is a mixture of nitrite and nitrate. Denitrifying bacteria then covert both nitrite and nitrate into nitrogen gas (N2). The overall result is the conversion of ammonia, a harmful water pollutant, into harmless nitrogen gas, the major component of Earth's atmosphere. Each step of nitrification/oxidation and denitrification/reduction requires resources, in the form of energy, aerated oxygen, and an electron source such as methanol.
The annual costs of treating U.S. wastewater alone are estimated to be $25 billion and escalating. It is also estimated that many more billions will be needed in future decades to maintain and replace ageing infrastructure. Furthermore, expanding wastewater infrastructure to accommodate an increasing population adds to this cost. Globally, there is an urgent need for lower-cost water treatment technologies in developing countries and rural areas.
If engineering based control of nitrification could be achieved to result in partial oxidation of ammonia solely to nitrite, it is estimated that a 25% savings in aeration cost could be realized. Correspondingly, denitrification based on nitrite rather than nitrate could result in up to a 40% savings on electron donor costs.