Biological nutrient removal was operated at different solids (SRT) and hydraulic retention times (HRT) in order to assess their influence on nitrous oxide (N2O) emission from a hybrid moving-bed membrane bioreactor. The observed results show that the N2O production decreased when the SRT/HRT was decreased. The maximum N2O gaseous concentration was measured in the aerobic reactor at the end of phaseI, and it decreased through phasesII and III. From mass balances over the reactors of the system, the aerated (aerobic and membrane) reactors were the largest producers of N2O, showing that the greater part of N2O was produced during the nitrification process.