The impact of using dead-end filtration conditions to sustain permeability in an immersed denitrification membrane bioreactor (MBR) has been studied, and the performance compared with a more conventional MBR hydrodynamic regime using constant gas sparging. Shear imparted during constant gas sparging was sufficient to reduce median floc size (d(50)) from 182 mu m. observed during dead-end filtration, to 55 mu m. Although this reduction in floc size demonstrated erosion, a concomitant generation of soluble extracellular polymeric substance (EPS) was not observed. Whilst unexpected, this finding accords with several recent investigations studying the long-term effect of shear. However, a significant concentration of soluble EPS was recorded in the biofilm that developed when using constant gas sparging (44.0% cf. 18.8% for dead-end) and was explained by the preferential transport of soluble compounds to the membrane wall during constant shear conditions. For an imposed flux (J(20 degrees C)) of 22 Lm(-2) h(-1), a fouling rate (dP/dt) of 0.39 mbar h(-1) was recorded during constant gas sparging compared to 0.11 mu bar h(-1) during dead-end filtration. The lower fouling rate recorded during dead-end conditions was sustained using only a 30s gas sparge at the end of each dead-end filtration cycle (ca. 10-30 min) which appeared sufficient to almost completely remove the cake layer formed. The reversibility of the cake was attributed to the simultaneous deposition of soluble, colloidal and flocculant materials which created a more heterogeneous, porous and subsequently less tenacious deposit. Cycle length, rather than gas flow rate, was identified as the critical parameter for optimum dead-end filtration; provided filtered volume was sufficiently short to limit mass deposition, low gas flow rates were sufficient to reverse deposition. This significantly impacts on energy demand; dead-end filtration provides a net energy reduction for gas sparging from 0.19 kWh m(-3) for constant sparging to 0.007 kWh m(-3). (C) 2010 Elsevier B.V. All rights reserved.