Dead-end and cross-flow ultrafiltration of ionic and non-ionic surfactants

Different molecular weight cut-offs (MWCO = 2–30 kDa) flat sheet membranes and hollow fibre modules were applied for filtration of surfactant aqueous solutions (Triton QS-44, CTAB and Triton X-100). The experiments were performed in a stirred cell (dead-end regime) and in a semi-pilot membrane installation (cross-flow regime). The effect of the process conditions (transmembrane pressure and cross-flow velocity) and the interaction between the membranes’ polymer and surfactants under a wide range of concentrations on ultrafiltration effectiveness was evaluated. The results demonstrated that the highest retention coefficient of anionic and cationic surfactants was obtained with the hydrophobic membranes; however, hydrophilic membranes were characterised by distinctly higher retention of the non-ionic surfactant. It was proved that with a good adjustment it is possible to determine, with the help of a linear dependence, the concentration of a surfactant in the permeate depending on the concentration in the feed solution.