In this study a University of Cape Town (UCT) Integrated Fixed Film Activated Sludge (IFAS) Membrane BioReactor (MBR) wastewater treatment plant was monitored in terms of nitrous oxide (N₂O) emissions. The short term effect on the N₂O emission due to the influent carbon-to-nitrogen (C/N) ratio variation (C/N ratios of 2, 5 and 10 gCOD/gN) was evaluated. Since in a previous study, the effect of the C/N ratio was studied in the same system without biofilm (UCT-MBR configuration) the main aim here was to investigate the role of biofilms on N₂O emissions. Under all the investigated C/N ratios, the N₂O fluxes and the average emission factors were lower than that of previous studies with no biofilm presence. The total average N₂O emission was 0.5% of the influent nitrogen with biofilm (IFAS system) and 3.5% without biofilm. This result emphasizes the potential role of the biofilms in attenuating the N₂O emissions especially in the case of stress conditions (i.e., low C/N influent ratios). An increase of N₂O flux from the anoxic reactor (till 28 mgN₂O m^-2h^-1) occurred at the lowest influent C/N tested (2 gCOD/gN - phase III). At C/N equal to 2 gCOD/gN the anoxic reactor was the main source of N₂O, contributing 45% of all produced N₂O. This result was attributed to an incomplete denitrification caused by a lack of organic carbon and a slight increase of dissolved oxygen concentration.