Metal removal efficiency by MEUF depends on the characteristics and concentrations of the metals and surfactants, solution pH, ionic strength, and parameters related to membrane operation. Landaburu-Aguirre et al. (2009) investigated the removal of zinc from synthetic wastewater by MEUF using SDS. They found that rejection coefficients up to 99% were achieved when the surfactant to metal molar ratio (S/M) was above 5. Sampera et al. (2009) used MEUF to remove Cd²⁺, Cu²⁺, Ni²⁺, Pb²⁺ and Zn²⁺ from synthetic water using two anionic surfactants: SDS and linear alkylbenzene sulfonate (LAS) in a lab-scale membrane system. The molar concentration ratio of the surfactant to metal is higher than 5 in all the experiments. When the initial SDS concentration was below the CMC, metal retention higher than 90% was unexpectedly obtained, except for Ni²⁺. Moreover, it was shown that complete removal of metal ions, except for Ni²⁺, could be achieved at an LAS concentration below CMC.