Soluble microbial products (SMP) in the sludge water phase are regarded as the main foulant in MBRs. This study further developed an existing hydrodynamic model by incorporating energy consumption. The focus was on the cost-effectiveness of crossflow (CF) velocity in the control of submicron particle deposition. A sensitivity analysis showed that CF had the greatest impact on both particle backtransport and energy consumption. The other operational variables, i.e., dry solid content (DS), membrane tube dimension (D and L) and temperature (7) were generally less influential with respect to particle backtransport and energy consumption. Submicron particles were likely to deposit in side-stream MBRs, and the lowest backtransport velocity was found for particle radii around 0.1 mu m and CF below 0.5 m/s. A particle size distribution (PSD) profile of MBR sludge showed a main peak at 40 mu m and a second peak at 0.1 - 1 mu m. The abundance of submicron particles at 2000 kDa was confirmed by a Liquid chromatography-Organic Carbon Detection (LC-OCD) analysis. The colloids responsible for the second peak in the PSD received high weighting factors (high filter cake formation potential) in the model optimization. In a lab-scale MBR, this critical crossflow velocity was between 0.75 and 1 m/s at 40 L/(m(2) h). (c) 2007 Elsevier B.V. All rights reserved.