Identifying sources of nitrous oxide emission in anoxic/aerobic sequencing batch reactors (A/O SBRs) acclimated in different aeration rates.

Both long term and batch experiments were carried out to identify the sources of the N(2)O emission in anoxic/aerobic sequencing batch reactors (A/O SBRs) under different aeration rates. The obtained results showed that aeration rate has an important effect on the N(2)O emission of A/O SBR and most of the N(2)O was emitted during the aerobic phase. During the anoxic phase, nitrate ammonification was the major source of N(2)O emission while denitrification performed as a sink of N(2)O, in all three bioreactors. The N(2)O emission mechanisms during the aerobic phase differed with the aeration rate. At low and high aeration rates (Run 1 and Run 3), both coupled-denitrification and nitrifier denitrification were ascribed to be the source of N(2)O emission. At mild aeration rate (Run 2), nitrifier denitrification by Nitrosomonas-like ammonia oxidizing-bacterial (AOB) was responsible for N(2)O emission while coupled-denitrification turned out to be a sink of N(2)O because of the presence of inner anaerobic region in sludge flocs.