Effect of anoxic/aerobic phase fraction on N 2O emission in a sequencing batch reactor under low temperature

Abstract

Laboratory scale anoxic/aerobic sequencing batch reactor (A/O SBR) was operated around 15 °C to evaluate the effect of anoxic/aerobic phase fraction (PF) on N 2O emission. The ammonia removal exhibited a decrease trend with the increase of PF, while the highest total nitrogen removal was achieved at PF = 0.5. Almost all the N 2O was emitted during the aerobic phase, despite of the PF value. However, the net emission of N 2O was affected by PF. Under the premise of completely aerobic nitrification, the lowest N 2O emission was achieved at PF = 0.5, with a N 2O–N conversion rate of 9.8%. At lower PF (PF = 0.2), N 2O emission was stimulated by residual nitrite caused by uncompleted denitrification during the anoxic phase. On the other hand, the exhaustion of the easily degradable carbon was the major cause for the high N 2O emission at higher PF (PF = 0.5). The N 2O emission increased with the decreasing temperature. The time-weighted N 2O emission quantity at 15 °C was 2.9 times higher than that at 25 °C.