Effluent from the secondary treatment of municipal wastewater was treated with membrane filtration to reduce its toxicity. Five different inorganic membranes were tested, namely, an a-alumina microfiltration membrane, an anatase titania ultrafiltration membrane, a gamma-alumina nanofiltration membrane, an amorphous titania nanofiltration membrane, and an amorphous hybrid organo-silica membrane. The permeabilities and selectivities (color, UV254-absorbing components, conductivity and inorganic nitrogen compounds) of the membranes were determined, and the gamma-alumina nanofiltration membrane was found to be the most promising membrane for the treatment of the effluent. The effluent flux was measured to be approximately 40 L m(-2) h(-1) for the gamma-alumina nanofiltration membrane, and it removed nearly 75% of the UV254-absorbing components and 15% of the ions. It also removed 40% of the CuCl and 25% of the CuSO4 from the spiked effluent. The fouling resistance was less pronounced for the gamma-alumina membrane compared with the other membranes. The removal of fecal indicator bacteria was determined by measuring the amounts of Escherichia coli and Enterococci, and the removal of toxic compounds was investigated in bioassays with Daphnia magna and Aliivibrio fischeri. The gamma-alumina nanofiltration membrane reduced the wastewater concentration of E. coli (97.3%) and Enterococci (98.4%), and the bioassays demonstrated that filtration with the gamma-alumina nanofiltration membrane reduced the overall toxicity of the effluent.