Effects of DO on N2O emission during biological nitrogen removal using aerobic granular sludge via shortcut simultaneous nitrification and denitrification.

Dissolved oxygen (DO) is an important factor influencing biological nitrogen removal. This study investigated the effects of different DO concentrations (4, 2, 1 mg/L) on nitrous oxide (N2O) production and nitrogen removal via shortcut simultaneous nitrification and denitrification by aerobic granular sludge (SNDAG) using a sequencing bath reactor. The results showed that N2O production was highest (127.6 mg/m3) at a DO concentration of 2 mg/L; this was 24.17 and 2.90 times the production at DO concentrations of 4 and 12 mg/L, respectively. The removal efficiency of total nitrogen also was the highest (61.68%) when the DO concentration was 2 mg/L, compared to 35.22% and 50.65% at DO concentrations of 4 and 1 mg/L, respectively. The efficiency of the SNDAG process reached 53.86% at a DO concentration of 2 mg/L, which was 1.33 and 1.67 times the efficiencies at DO concentrations of 4 and 1 mg/L, respectively. Therefore, reducing the DO concentration benefited the SNDAG process, but increased the emission of N2O.