Effects of solution environment on humic acid fouling during microfiltration

Microfiltration is increasingly used in drinking water treatment for the re moval of particles, turbidity, and microorganisms to meet more stringent wa ter quality requirements. Fouling by natural organic matter (e.g., humic an d fulvic acids) is a critical factor in microfiltration processes. Experime nts were performed to evaluate the effects of solution pH, salt concentrati on, and ionic composition on the extent and mechanisms of humic acid foulin g during microfiltration. Fouling was more severe at high salt concentratio n due to the tighter packing of the charged humic acids within the fouling layer caused by the increased electrostatic shielding. The effects of solut ion pH were more complex and likely reflect alterations in humic acid charg e, hydrophobicity, and extent of aggregation. Divalent cations such as calc ium significantly increased humic acid fouling and aggregation through the formation of intra- or intermolecular bridges between the negatively charge d humic acid molecules. These results provide important insights into the p hysical and chemical interactions governing humic acid fouling during micro filtration.