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

Quantities of nitrous oxide, N2O, an important greenhouse gas, were fo und in the effluent gases from controlled continuous aerobic treatment of pig slurry. Where nitrifying-denitrifying conditions were encourag ed (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 acc ounted for 19% of the nitrogen lost from the slurry. Smaller concentra tions of the gas (170 ppm) were found during short treatments (1.5 day s) where nitrifying activity would not be expected; partial nitrificat ion is a possible explanation. Quantities of nitric oxide (NO) (up to 100 ppm), and even small amounts of NO2, were also found, suggesting t hese previously unquantified nitrogen transformation routes in the tra ditional nitrogen cycle exist in aerobic treatment processes.