AWWA JAW31494

Numerical simulations and experimental work for evaluating transport mechanisms for colloidal foulants in pressure-driven membrane systems are discussed. A model for concentration polarization is used to explore the role of ionic strength in determining the distribution of dissolved humic materials near a rejecting membrane. Particle trajectory theory predicts that there should exist a critical particle size above which particles will not deposit on the membrane. For conditions typical of ultrafiltration and microfiltration, which operate in laminar flow and utilize an inside-out geometry, this critical particle diameter is likely to be in the range of 10-50 um. Qualitative evidence, based on measurements of permeate flux, supports the theoretical minimum in diffusive back-transport of particles predicted to occur for particles near 0.1 um in size. Includes 24 references, figures.