The purpose of this study is to investigate, through fractionation experiments, the efficiency with which secondary effluents can be treated using OF and MF membranes alone or coupled with coagulation and/or adsorption. The results obtained prove that there are two mains fractions in a secondary effluent: colloids and infra-colloids retained by an MF membrane (0.1 micron pore size) and solutes (which cross a membrane of 10 000 Dalton cut-off). Adsorption is mainly efficient for removing the solutes, whereas coagulation allows MF membranes to be as efficient as OF membranes while providing a higher and better controlled permeate flux.