FLUX AND REJECTION IN THE ULTRAFILTRATION OF COLLOIDS

Charge on colloidal particles is shown to affect the filtration process in two ways. The effect of changing the charge of the particles, such as by varying pH, is to alter the observable flux which goes through a minimum as the charge is increased. At fixed charge the flux first decreases with particle size and then increases. Charge also influences the mechanism of particle rejection. If primary particles are stable colloids, smaller than the surface pores, they may penetrate the membrane but not necessarily pass all the way through. When particle charge is low enough for flocculation to be significant, rejection will most likely occur at the membrane surface as flocculation results in particles growing to become large enough to be rejected.