Formation of nitrous oxide in a gradient of oxygenation and nitrogen loading rate during denitrification of nitrite and nitrate

► The correlation of DO to N2O emission under denitrification via nitrite was confirmed. ► The higher nitrite ratio in NOx (nitrite and nitrate) caused the more N2O emission. ► Reactor feed mode and nitrite loading rate had significant impact on N2O emission which was related to nitrite level.