Time-resolved characteristics and production pathways of simulated landfilling N2O emission under different oxygen concentrations

Abstract

Nitrous oxide (N2O), an important greenhouse gas, is emitted from landfill reservoirs, especially in the working face, where nitrification and denitrification occur under different O2 concentrations. In order to explore the effects of O2 concentration on N2O emissions and production pathways, the production of N2O from simulated fresh waste landfilling under 0%, 5%, 10%, and 21% (vol/vol) O2 concentrations were examined, and 15N isotopes were used as tracers to determine the contributions of nitrification (NF), heterotrophic denitrification (HD), and nitrification-coupled denitrification (NCD) to N2O production over a 72-h incubation period. Equal amounts of total nitrogen consumption occurred for all studied O2 concentration and the simulated waste tended to release more N2O under 0% and 21% O2. Heterotrophic denitrification was the main source of N2O release at the studied oxygen concentrations, contributing 90.51%, 69.04%, 80.75%, and 57.51% of N2O under O2 concentrations of 0%, 5%, 10%, and 21%, respectively. Only denitrification was observed in the simulated fresh waste when the oxygen concentration of the bulk atmosphere was 0%. The nitrate reductase (nirS)-encoding denitrifiers in the simulated landfill were also studied and significant differences were observed in the richness and diversity of the denitrifying community at different taxonomic levels. It was determined that optimising the O2 content is a crucial factor in N2O production that may allow greenhouse gas emissions and N turnover during landfill aeration to be minimised.