| Abstract
| - Recent studies have shown that natural organic matter(e.g., humic and fulvic acids) is a major foulant duringultrafiltration of surface water. The objective of this studywas to develop a more complete understanding of themechanisms governing humic acid fouling, including theeffects of humic acid adsorption, concentration polarization,and aggregate deposition on the rate and extent offouling. Data were obtained with Aldrich and SuwanneeRiver humic acids using ultrafiltration membranes with abroad range of molecular weight cutoffs. Fouled membraneswere also examined using streaming potential andcontact angle measurements. The extent of flux declinewas greatest for the largest molecular weight cutoffmembranes due to the greater relative hydraulic resistanceof the humic acid deposit formed on the surface ofthese membranes. This humic acid deposit reduced theapparent zeta potential and increased the membrane contactangle. Simple static adsorption and concentrationpolarization caused relatively little flux decline. Humicacid aggregates had a significant effect on fouling onlyfor the larger molecular weight cutoff membranes. The rateand extent of humic acid fouling increased at low pH,high ionic strength, and in the presence of calcium dueto changes in intermolecular electrostatic interactions. Theseresults provide important insights into the mechanismsof humic acid fouling during ultrafiltration.
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