Separation of humic acid from a model surface water with PSU/SPEEK blend UF/NF membranes

Membranes made from blends of polysulphone and sulphonated poly(ether ether ketone) (PSU/SPEEK) have high porosity, high charge and a pore size at the boundary between nanofiltration (NF) and ultrafiltration (UF). Their application to the treatment of surface water for drinking purposes has been investigated through study of their ability to remove humic acid (HA) from a model water, in comparison with two commercial membranes. The PSU/SPEEK membranes, in planar or tubular form, showed excellent retention of HA and very high flux. Their high charges gave rise to critical fluxes for deposition. As an additional benefit, HA deposits forming on the charged membranes above the critical fluxes had a loose structure, as visualised by atomic force microscopy (AFM), and were consequently efficiently removed by rinsing. Three multivalent ions, Fe3+, Al3+ and Mn2+, at their concentrations in a natural water did not affect the membrane process significantly.