Quantifying N₂O emissions and production pathways from fresh waste during the initial stage of disposal to a landfill

Intensive nitrous oxide (N₂O) emissions usually occur at the working face of landfills. However, the specific amounts and contributions of the multiple pathways to N₂O emissions are poorly understood. N₂O emissions and the mutual conversions of N-species in both open and sealed simulated landfill reactors filled with fresh refuse were examined during a 100-h incubation period, and N₂O sources were calculated using ¹⁵N isotope labelling. N₂O peak fluxes were above 70μgNkg^-1 waste h^-1 for both treatments. The sealed incubation reactors became a N₂O sink when N₂O in the ambient environment was sufficient. The total amount of N₂O emissions under sealed conditions was 2.15±0.56mgNkg^-1 waste, which was higher than that under open conditions (1.91±0.34mgNkg^-1 waste). The NO₂^- peak appeared prior to the peak in N₂O flux. The degree and duration of total nitrogen reduction in open incubations were larger and longer than those of sealed incubations and could possibly be due to oxygen supplementation. Denitrification (DF) was a major source of N₂O generation during these incubations. The contribution of the DF pathway decreased from 89.2% to 61.3% during the open incubations. The effects of nitrification (NF) and nitrification-coupled denitrification (NCD) increased during the increasing phase and the decreasing phase of N₂O flux, contributing 24.1-37.4% and 31.7-34.4% of total N₂O emissions, respectively. In sealed treatments, the DF pathway accounted for more than 90% of the total N₂O emission during the entire incubation.