Characteristics and key driving factors of nitrous oxide emissions from a full-scale landfill leachate treatment...

The characteristics of N₂O emission from a full-scale landfill leachate treatment system were investigated by in-situ monitoring over 1.4 years and driving factors responsible for these emissions were identified by statistical analysis of multidimensional environmental variables. The results showed that the maximum N₂O emission flux of 2.21 × 10⁷ mg N·h^-1 occurred in the nitrification tanks, where 98.5 % of the total N₂O was released, with only 1.5 % of the total N₂O emitted from the denitrification tanks. Limited oxygen in nitrification tank was responsible for N₂O hotspot. The N₂O emissions from the parallel lines A and B (both comprising the primary biochemical system) accounted for 52.6 % and 46.6 %, respectively, while the secondary biochemical system contributed only 0.8 % to the total emissions. Higher nitrite concentration in line A and lower nitrogen loading in the secondary biochemical system caused these discrepancies. We found that during the steady state of leachate treatment, intensive N₂O emissions of 253.4-1270.5 kg N·d^-1 were measured. The corresponding N₂O emission factor (EF) ranged from 8.86 to 49.6 %, much higher than those of municipal wastewater treatment. But N₂O EF was inconceivably as low as 0.42 % averagely after system maintenance. Influent with low salinity was the key reason, followed by the high MLSS and varying microbial community after maintenance. The dominant genus shifted from Lentimicrobium and Thauera to Norank-F-Anaerolineaceae and Unclassified-F-Rhodocyclaceae. This study underscores the significance of landfill leachate treatment in urban nitrogen management and provides valuable insights into the characteristics and driving factors of N₂O emissions from such systems. The findings offer important references for greenhouse gas emission inventories and strategies for N₂O control in full-scale wastewater treatment plants.