Wastewater samples from eight membrane biological reactors (MBR) and four activated sludge plants (AS) were taken. Bench scale membrane filtration tests using both a stirred cell and cross flow apparatus were performed. Computational fluid dynamic (CFD) models for both modules were created using FLUENT ® v6 to accurately characterize module hydrodynamics. Wastewater properties, including dissolved and extracted EPS, were analyzed to identify the most important characteristics influencing membrane fouling. Steady state permeate flux for cross flow and stirred cell tests ranged from 6 to 29 Lm -2h-1 and 17 to 115 L-2h-1 respectively. Total dissolved carbohydrates negatively influenced permeate flux at values below 20 mg/L. In general, MBR samples had lower permeate fluxes compared to AS samples. This was due to larger total dissolved carbohydrate concentrations and increased numbers of particles with average diameters between 1 and 2.6 [mu]m.