An artificial fouling method was used to study the effect of suspended particulates on the performance of standard asymmetric cellulose acetate membranes in flat cells. Using a modified filtration theory developed here, membrane and cake resistances to permeation were individually monitored as a function of applied pressure, membrane curing temperature, and feed type. The membranes behaved according to the solution-diffusion model. A new previously unreported method of membrane protection — the protective cover method — for submicron colloidal solutions, resulted in as high as 78% increased fluxes and 43% decreased salt rejections, over the unprotected membrane. This development is applicable where low salt rejection and high fluxes are desired such as in industrial and municipal wastewater renovation.