Membrane retention was investigated with the aid of poly diallydimethylammonium chloride and copolymer of dimethyl aminoethyl acrylate polyelectrolyte coagulants The membranes used were P005F ultrafiltration (UF) and NF270 nanofiltration (NF) membranes and the studied conditions were salinity level. humic substances (HS) concentration, heavy metals concentration and polyelectrolytes type and concentration Results showed that with the aid of polyelectrolytes. HS retention reached a maximum point where further increase in polyelectrolytes degraded membrane retention This study showed also that at low polyelectrolyte concentration. salinity reduced membrane retention While at Optimum polyelectrolytes dose. membrane performance was not affected by salinity In addition. HS binding capacity for heavy metals was reduced considerably at high salinity levels. (C) 2009 Elsevier B.V All rights reserved