Membrane Filtration of Coagulated Suspensions

The deposition of small colloids or macromolecules in membrane pores and the subsequent irreversible fouling of the membrane is considered using a simple model for membrane fouling. As a strategy for avoiding pore fouling, it is proposed that foulants capable of entering membrane pores be aggregated to produce particles that are rejected at the membrane surface. Considerations in filtering suspensions of particles on membranes are discussed with emphasis on particle transport mechanisms as a function of particle size. It is concluded that particles larger than 3 μ\Nm should not contribute significantly to membrane fouling at permeate fluxes that are currently feasible. For many membrane configurations, particles between 0.1 and 1 μ\Nm will be most likely to contribute to fouling on membrane surfaces. Batch flocculation and membrane filtration experiments were conducted to test the feasibility of manipulating flocculation conditions to control particle size and fouling. Conditions that produced particles with a zeta potential near zero minimized fouling by reducing foulant penetration into pores, increasing the porosity of the deposited cake, and increasing the transport of potential foulants away from the membrane.