Poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM-co-AA) hydrogels with thermo-responsive properties were used as water-soluble polymer in a polymer-enhanced ultrafiltration (PEUF) process. The hydrogel-metal complexes were retained by cellulose acetate UF membrane (MWCO=20 kDa) and their fouling behaviour were investigated at different pH and temperature. It was found that at lower temperature ( <40 degrees C), the retention of copper ion is superior compared to higher operating temperature. It provided more than 98% retention at pH 5 for 50 ppm of Cu2+ using 0.5 g L-1 PNIPAM-co-AA. Membrane at higher temperature showed the least fouling phenomenon as observed from the drastic increased of permeation flux. At higher temperature, the collapsed hydrogels became more hydrophobic therefore not favouring the interactions with the hydrophilic membrane surface. (C) 2014 Elsevier B.V. All rights reserved.