COLLOID DEPOSITION RATES ON SILICA BED MEDIA AND ARTIFACTS RELATED TO COLLECTOR SURFACE PREPARATION METHODS

Colloid deposition rates in porous media under unfavorable filtration conditions were compared for filter media cleaned by a variety of methods. The bed media consisted of soda-lime glass beads or ultrapure quartz sand, and the colloids were 0.245-gm-diameter carboxyl latex spheres. Deposition rates, expressed as attachment efficiencies, a, were determined as a function of pH at constant ionic strength. The filter media were cleaned with strong acid (HCI) alone, strong acid in combination with concentrated chromic acid, heat (810-degrees-C), acetone, or boiling 4 N HNO3. Filter media treated with the two most aggressive oxidation methods, combustion and chromic acid, yielded attachment efficiencies that were significantly more sensitive to solution chemistry changes and the lowest a values. Zeta potentials of the filter media, however, were independent of the treatment methods. Deposition rates were also compared for two bed media size fractionation methods, sieving and a wet-sedimentation technique. Sieving irreversibly enhanced particle deposition rates. Electrophoresis measurements indicate that soda-lime glass surfaces undergo relatively slow hydration, which complicates their characterization.