Abstract:Investigations on greenhouse gases (GHGs) emissions and pollutant removal performance during simultaneous nitrification and denitrification (SND) process were conducted in anoxic-oxic sequencing batch reactors. Total nitrogen removal rate of SND process was 90.39%, significantly higher than that of sequential nitrification and denitrification (SQND) process, which was 63.78%. SND process enhanced GHGs emissions. The total GHGs emissions during per SND cycle were about 4.5 times higher than that during per SQND cycle. About 34.28 mg nitrous oxide (N2O) was produced per SND cycle, almost 5 times higher than that during SQND process, which was 6.89 mg N2O per cycle. N2O emission was mainly occurred during the oxic phase in both processes. The carbon dioxide (CO2) emission from SND and SQND processes was 493.52 and 320.28 mg per cycle, respectively.And both processes showed a near-zero methane (CH4) emission.