N2O production from wastewater by ammonium oxidising bacteria

Nitrous oxide is a potent greenhouse gas produced as a by-product of wastewater treatment. Current literature focuses on production of nitrous oxide by denitrifying bacteria. There is evidence that the nitrifying bacteria commonly found in soils can also produce nitrous oxide. This study investigates' the ability of nitrifying bacteria from local wastewater treatment plants to produce nitrous oxide and which conditions induce this production. This study shows that a significant proportion of nitrous oxide formation in wastewater treatment plants is produced by nitrification. Ammonium oxidising bacteria produce nitrous oxide at their maximum rate when DO was in the range of 0.1 - 1.0 mg/1 and pH was 8-8.5. Increasing nitrite concentrations also increased nitrous oxide formation by AOB up to a nitrite concentration of 2.0 rnM, the maximum tested in this study. Nitrous oxide formation rates by AOB reached 6.0 uM/minute/ under optimal conditions with. Nitrous oxide production by ammonium oxidising bacteria introduces the possibility of a new pathway for nitrogen removal, SND via N20. This involves the transfer of nitrous oxide produced to denitrifiers for reduction to dinitrogen gas. Using mathematical models transfer of nitrogen from AOB to denitrifiers is theoretically possible. The demonstration of this principle was masked by the apparent ability of denitrifiers to induce nitrous oxide production when in the presence of hydroxylamine, a chemical intermediate in nitrite and nitrous oxide production in AOB