Critical evaluation of different mass transfer equations to model N₂O emissions from water resource recovery...

N₂O measurements by liquid sensors in aerated tanks are an input to gas-liquid mass-transfer models for the prediction of N₂O off-gas emissions. The prediction of N₂O emissions from Water Resource Recovery Facilities (WRRFs) was evaluated by three different mass-transfer models using Benchmark Simulation Model 1 (BSM1) as a reference model. Inappropriate selection of mass-transfer model may result in miscalculation of carbon footprints based on soluble N₂O online measurements. The film theory considers a constant mass-transfer expression, while more complex models suggest that emissions are affected by the aeration type, efficiency, and tank design characteristics. The differences among model predictions were 10-16% at dissolved oxygen (DO) concentration of 0.6 g/m³, when biological N₂O production was the highest, while the flux of N₂O was 20.0-24 kg N₂O-N/d. At lower DO, the nitrification rate was low, while at DO higher than 2 g/m³, the N₂O production was reduced leading to higher rates of complete nitrification and a flux of 5 kg N₂O-N/d. The differences increased to 14-26% in deeper tanks, due to the pressure assumed in the tanks. The predicted emissions are also affected by the aeration efficiency when K_La_N2O depends on the airflow instead of the K_La_O2. Increasing the nitrogen loading rate under DO concentration of 0.50-0.65 g/m³ increased the differences in predictions by 10-20% in both alpha 0.6 and 1.2. A sensitivity analysis indicated that the selection of different mass-transfer models did not affect the selection of biochemical parameters for N₂O model calibration.