EMISSIONS OF NITROGEN-OXIDE GASES DURING AEROBIC TREATMENT OF ANIMAL SLURRIES

Quantities of nitrous oxide, N2O, an important greenhouse gas, were found in the effluent gases from controlled continuous aerobic treatment of pig slurry. Where nitrifying-denitrifying conditions were encouraged (4-day treatment time and aeration to a redox potential of - 50 mV E(cal)), concentrations of this gas at times exceeded 1500 ppm and accounted for 19% of the nitrogen lost from the slurry. Smaller concentrations of the gas (170 ppm) were found during short treatments (1.5 days) where nitrifying activity would not be expected; partial nitrification is a possible explanation. Quantities of nitric oxide (NO) (up to 100 ppm), and even small amounts of NO2, were also found, suggesting these previously unquantified nitrogen transformation routes in the traditional nitrogen cycle exist in aerobic treatment processes.