Cellulose acetate (CA) ultrafiltration membranes were functionalized using a green chemistry approach. In the functionalization, an enzyme. Porcine pancreatic crude type II lipase (PPL), was used to poly-condensate poly ethylene glycol (PEG) to the surface of the CA membranes. Modification was verified using structural and morphological analyses. The unmodified and the modified membranes displayed similar initial flux values, flux decline curves and rejection efficiencies when dextran and bovine serum albumin (BSA) were used as feed solutions. This was likely due to the high degree of hydrophilicity and similar charge characteristics between the modified and unmodified membranes. However, when natural organic matter (NOM) was filtered through the membranes, it was determined that modification led to lower cake accumulation on the surface of the modified membrane, to lower flux declines during operation, while NOM rejection remained unchanged. Furthermore, after backwashing, the modified membrane regained nearly 97% of its initial flux value within 40 min of filtration, while the unmodified membrane recovered only 85%. This improvement is possibly due to the high flexibility of the PEG chains grafted. Therefore, the use of PPL to polycondensate PEG to a CA membrane was deemed a successful functionalization process to decrease NOM fouling. (C) 2010 Elsevier B.V. All rights reserved.