Nitrous oxide (N_2O) emissions from biotrickling filters used for ammonia removal at livestock facilities

摘要

Recently several manufacturers of nitrifying biotrickling filters for ammonia (NH_3) removal at animal houses have started to add a denitrification step to the installation, aiming to reduce the amount of discharge water by conversion of NH_3 to nitrogen gas (N_2). The aim of this research was to quantify the possible formation of nitrous oxide (N_2O), which is a potent greenhouse gas, in three of these farm-scale installations. Furthermore, the removal efficiency of NH_3 and odor was determined. All installations were successful in reducing the amount of discharge water. The average NH_3 removal efficiency for the three locations was 85, 71 and 86%, respectively. However, a significant part of the NH_3 removed from the inlet air was not converted to N_2 but to N_2O, which is a potent greenhouse gas. The part of the inlet NH_3-N that was converted to N_2O-N amounted to 17, 66 and 24%, respectively. The high N_2O production might have been caused by a too lowscarcity of biodegradable carbon/N ratio for complete denitrification. The average odor removal efficiency was 21, 32 and 48%, respectively. Further research is necessary to explore how process conditions can be adjusted and controlled in order to reduce the production and emission of N_2O from these types of systems.