EFFECT OF ADSORPTION OF ORGANIC-MATTER ON FOULING OF ULTRAFILTRATION MEMBRANES

This study examined the effect of organic matter adsorption on ultrafiltration membrane blocking and fouling. A hydrophilic cellulose derivative membrane and a hydrophobic acrylic polymer membrane, both with a hollow fiber configuration, were tested. The experiments were performed using synthetic, particle free solutions of a low molecular weight dextran and tannic acid. The effect on fouling of pretreatment of the synthetic solutions by preozonation and by preadsorption on powder activated carbon (PAC) was also evaluated. The level of adsorption was assessed by measuring the quantity of each compound adsorbed, reversibly or irreversibly, by mass or per surface unit of membrane. The level of fouling was assessed by monitoring the loss in specific flux under actual filtration conditions. The study showed that the highest level of adsorption occurred in the ultrafiltration of the aromatic compounds through the hydrophobic membrane. The filtration of a 15 mg/l tannic acid solution led to the adsorption of 6 mg of tannic acid per gram of dry membrane. This resulted in severe fouling with an 80 percent loss of initial flux after only three hours of filtration, despite the absence of particulate matter. Preozonation was very effective in preventing adsorption of tannic acid by-products on the hydrophilic membrane, but only partially reduced the fouling caused by adsorption of the hydrophobic membrane. Similarly, preadsorption on PAC was effective when the membrane used for subsequent filtration was hydrophilic.