The aim of the present work was to study the retention properties of arsenate and phosphate at various feed concentrations and to investigate the effect of pH on the rejection of these ions through modified polyacrylonitrile (PAN) ultrafiltration membrane. In one component solution with feed concentration of 10 ppm arsenate and phosphate separately showed >= 90% rejection at >= pH 7 with PAN UF as well as nanofiltration membranes. Similarly, the mixture of arsenate and phosphate showed more than 90% rejection for feed concentration of 100 ppm each. However, the arsenate rejection decreased to 55-60% for 10 ppm arsenate and 100 ppm phosphate mixture in the feed, while phosphate rejection remained >= 90%. The rejection of arsenate and phosphate reversed to >= 90% and similar to 60% respectively for 100 ppm arsenate and 10 ppm phosphate in the feed. The solution pH played an important role in changing the membrane surface properties. The rejection coefficient of arsenate and phosphate varied from 5% to 95% by changing pH between 3 to 10. Donnan steric-partitioning pore model incorporating dielectric exclusion used to investigate the arsenate rejection and good agreement was found between experimental and simulated data. (C) 2014 Elsevier B.V. All rights reserved.