In MBR processes, sufficient aeration is necessary to maintain sustainable flux and to retard membrane fouling. Membrane permeability, sludge characteristics, nutrient removal and biomass growth at various air flow rates in the membrane and moving bed biofilm reactor (MBBR) compartments were studied in a pilot plant. The highest nitrogen and phosphorous removal rates were found at MBBR aeration rates of 151 and 85 L h(-1) and a specific aeration demand per membrane area (SAD(m)) of 1.2 and 0.4 m(air)(3) m(-2) h(-1), respectively. A linear correlation was found between the amount of attached biofilm and the nutrient removal rate. The aeration rate in the MBBR compartment and SAD(m), significantly influenced the sludge characteristics and membrane permeability. The optimum combination of the aeration rate in the MBBR compartment and SAD(m), were 151 L h(-1) and 0.8-1.2 M-air(3) m(membrane)(-2) h(-1) respectively. (C) 2010 Elsevier B.V. All rights reserved.