Effects of solution environment on humic acid fouling during microfiltration

Microfiltration is increasingly used in drinking water treatment for the removal of particles, turbidity, and microorganisms to meet more stringent water quality requirements. Fouling by natural organic matter (e.g., humic and fulvic acids) is a critical factor in microfiltration processes. Experiments were performed to evaluate the effects of solution pH, salt concentration, and ionic composition on the extent and mechanisms of humic acid fouling during microfiltration. Fouling was more severe at high salt concentration due to the tighter packing of the charged humic acids within the fouling layer caused by the increased electrostatic shielding. The effects of solution pH were more complex and likely reflect alterations in humic acid charge, hydrophobicity, and extent of aggregation. Divalent cations such as calcium significantly increased humic acid fouling and aggregation through the formation of intra- or intermolecular bridges between the negatively charged humic acid molecules. These results provide important insights into the physical and chemical interactions governing humic acid fouling during microfiltration.