Dinitrogen oxide production by a mixed culture of nitrifying bacteria during ammonia shock loading and aeration failure.

A number of experiments was conducted in order to establish if N(2)O in the exhaust gas from an aerobic consortium of nitrifiers could be used as an indicator for monitoring the nitrification process. Laboratory-scale experiments with an activated sludge system showed a strong correlation between ammonia shock loads and both the concentration of N(2)O and the rate of increase of N(2)O in the exhaust gas for shock loads less than 1.60 mg ammonical nitrogen (NH(3)-N) per g total suspended solids (TSS). For greater ammonia shock loads, correlation was found between build-up of nitrite in the aeration tank and the concentration of N(2)O in the exhaust gas from the tank. When subjecting the system to aeration failure, a similar pattern was seen, with a correlation between nitrite build-up in the aeration tank and increases in the concentration of N(2)O in the exhaust gas. The results from this work suggest that the changes in N(2)O concentration in the exhaust gas from a nitrifying process may be a useful parameter for monitoring such processes.

Production of nitrogen oxide and dinitrogen oxide by autotrophic nitrifiers.

Autotrophic nitrifiers have been shown to produce nitrogen oxide and dinitrogen oxide under oxic conditions. Dinitrogen oxide is produced mainly during nitrite reduction (i.e. aerobic denitrification) whereas nitrogen oxide is produced during both aerobic denitrification and as a result of chemodenitrification. Oxygen is the single most influential environmental factor affecting the production of nitrogen and dinitrogen oxides; a decrease in oxygen can result in a several-fold increase in nitrogen oxide and dinitrogen oxide production. Emission of nitrogen oxide and dinitrogen oxide from wastewater treatment plants and fertilized soils is well documented; however, only recently have the contributions from such environments to the global nitrogen and dinitrogen oxide budget been considered.