Simultaneous nitrification and denitrification (SND) was achieved in an MABR (membrane aerated biofilm reactor) system treating primary settled municipal sewage. Under ideal conditions, the total nitrogen (TN) concentration was reduced from approximately 50 mg/L to less than 5 mg/L. TN removal was highly variable ranging between 15 - 92% due to varying amounts of denitrification observed during the four seasons. One factor identified as impacting denitrification was the soluble biodegradable COD (sbCOD) to TN ratio. When the sbCOD/N ratio was reduced from 1.8 to 1.3, denitrification was limited as there was insufficient electron donor available to reduce nitrate to nitrogen gas. The availability of sbCOD was not the only factor that negatively impacted denitrification, also the ratio between the amount of oxygen supplied versus the oxygen demand (theoretical oxygen required for oxidation of all COD and TN) of the feed (O2/F ratio) played a role. When the O2/F ratio was high (4.9) (indicating an oversupply of oxygen) denitrification was limited in the MABR system, even when the sbCOD/N was in a good range (1.6 - 1.8). The results from this study demonstrate that simultaneous nitrification and denitrification can be realised using a pure standalone MABR system (i.e., no mixed liquor) and that the sbCOD availability and the O2 load supplied to the system versus the oxygen demand are critical to obtain effective simultaneous nitrification and denitrification (SND).