The fouling of microfiltration membranes by NOM after coagulation treatment

Microfiltration membranes used in drinking-water treatment are fouled by both colloidal material and natural organic matter (NOM) present in the raw water. The relative importance of these contributions to fouling may depend on whether or not the water is pretreated before microfiltration, and on the type and extent of any pretreatment. In this study, the causes of fouling were determined for microfiltration of a surface water through a polypropylene hollow-fibre membrane. Fouling was caused by colloidal material when the raw water was filtered untreated, and by NOM when the raw water was coagulated before filtration. The components of NOM which cause fouling of microfiltration membranes are not yet well-established, and were also investigated in this study. NOM from the raw water was fractionated into four specific classes of compounds on the basis of hydrophobicity and charge. The rates of fouling by each NOM fraction were measured separately. The major contribution to fouling was attributed to the NOM fraction comprising small, neutral, hydrophilic compounds. The NOM fractions comprising humic and fulvic acids made only a minor contribution to fouling.