This study investigates the removal of 11 emerging contaminants dissolved in ultrapure water or in municipal secondary effluent by ultrafiltration and nanofiltration membranes. The influence of the most important operating variables (nature and MWCO of the membranes, transmembrane pressure, tangential velocity, pH and temperature) on the permeate flux and on the retention of the selected compounds was discussed. Most of the emerging compounds presented retentions above 70% with the selected NF membranes. However, lower retention coefficients were obtained with the UF membranes tested (<50%, except for hydroxybiphenyl). According to the results obtained for membrane fouling, retention coefficients and adsorption of contaminants on the membranes, while adsorption is the main mechanism for micropollutants retention by UF filtration membranes, size exclusion and electrostatic repulsion at high pH are dominant in the case of NF membranes. In addition, retention coefficients for parameters that measure the quality of the effluent (chemical oxygen demand, absorbance at 254 nm, turbidity, total nitrogen and total phosphorus) were also evaluated, and the results revealed that both UF and NF are feasible options for the treatment of municipal secondary effluent, leading to a permeate stream that can be reused in several applications. (C) 2010 Elsevier B.V. All rights reserved.