Humic acid fouling during ultrafiltration

Recent studies have shown that natural organic matter (e.g., humic and fulv ic acids) is a major foulant during ultrafiltration of surface water. The o bjective of this study was to develop a more complete understanding of the mechanisms governing humic acid fouling, including the effects of humic aci d adsorption, concentration polarization, and aggregate deposition on the r ate and extent of fouling. Data were obtained with Aldrich and Suwannee Riv er humic acids using ultrafiltration membranes with a broad range of molecu lar weight cutoffs. Fouled membranes were also examined using streaming pot ential and contact angle measurements. The extent of flux decline was great est for the largest molecular weight cutoff membranes due to the greater re lative hydraulic resistance of the humic acid deposit formed on the surface of these membranes. This humic acid deposit reduced the apparent zeta pote ntial and increased the membrane contact angle. Simple static adsorption an d concentration polarization caused relatively little flux decline. Humic a cid aggregates had a significant effect on fouling only for the larger mole cular weight cutoff membranes. The rate and extent of humic acid fouling in creased at low pH, high ionic strength, and in the presence of calcium due to changes in intermolecular electrostatic interactions. These results prov ide important insights into the mechanisms of humic acid fouling during ult rafiltration.