An experimental study of particulate matter retention by microporous membranes during liquid filtration has been conducted using 0.1, 0.22, 0.45, and 0.65-μm-rated hydrophilic and hydrophobic membrane filters. Retention measurements have been made with polystyrene latex spheres using an automated filter test system and a laser particle counter to measure the upstream and downstream particle concentration.
Particle filtration during loading tests was found to begin with a sieving dominant regime followed by a transition regime and a cake filtration regime as particles accumulate inside the filter pores and on the filter surface. For latex sphere sizes equal to the nominal pore size of the filter, the initial filter efficiencies ranged from 97 to 99.9 percent. Complete retention (>99.9999999 percent) was achieved for a range of particle sizes two to three times the rated pore sizes of the filter. With the addition of a surfactant to the liquid, the retention was found to be lowered as a result of enhanced particle passage through the filter due to modified surface adsorption and steric stabilization. It was found that particle retention by sieving with the addition of surfactant provided the "worst-case" test for filter performance.