Influence of the characteristics of natural organic matter on the fouling of microfiltration membranes

Natural organic matter (NOM) plays a significant role in fouling microfiltr ation membranes in drinking water treatment processes even though the NOM i s retained only to a small extent. The aim of this study was to obtain a be tter understanding of the interactions between the fractional components of NOM and microfiltration membranes. Filtration experiments were performed u sing 0.22 mum hydrophobic and hydrophilic polyvinylidene fluoride (PVDF) me mbranes in a stirred-cell system on the NOM isolated from three Australian surface waters. As expected, the fouling rate for the hydrophobic membrane was considerably greater than for the hydrophilic membrane. Focusing on the hydrophobic membrane, it was shown that the high molecular weight fraction of NOM (> 30 kDa) was responsible for the major flux decline. Filtration t ests on the four fractions of NOM isolated on the basis of hydrophobicity a nd charge using non-functionalised and anionic resins revealed that the fou ling potential for the three waters was hydrophilic neutral > hydrophobic a cids > transphilic acids > hydrophilic charged. The low-aromatic hydrophili c neutral compounds were the main determinant of the rate and extent of flu x decline. This was linked to the colloidal size fraction (> 30 kDa) and to the selective concentration of calcium in the fraction leading to organics -Ca2+ bridging. It was also shown that the higher the aromaticity of the NO M the greater the flux decline, and the aromatics mainly resided in the hyd rophobic acids fraction. Overall, the fouling mechanism controlling the flu x decline involved the combined effects of adsorptive and colloidal fouling by the hydrophilic neutral fraction in the internal pore structure of the membrane. (C) 2001 Elsevier Science Ltd. All rights reserved.