Effects of aquatic humic substances on a hydrophobic ultrafiltration membrane

Natural humic surface water (pH 5.9), ion exchanged samples of the same wat er (pH 5.5), and aqueous solutions of isolated humic substances at pH 4.5, 5.5 and 6.5, respectively, were ultrafiltered (15 degrees C, 0.5 bar) using hydrophobic polysulfone membranes (GR51) in a cross-flow flat sheet module . The used membrane did not completely retain natural organic matter from t he surface water and the addition of complexing metals did not affect the r etention any further. The changes which were induced in the membranes durin g each filtration run were studied by simultaneous streaming potential and flux measurements in 0.01 M KCl solutions. Zeta potentials were calculated based on the streaming potentials and the results showed changes towards mo re negative values for all the samples due to adsorption of organic matter onto the surface of the membrane pores. Humic acid affected the membrane ch arges more than fulvic acid. High ionic strength and low pH enhanced flux r eduction and fouling. Filtration of natural waters caused more pore pluggin g and flux reduction than filtration of solutions of the isolated humic sub stances. (C) 1999 Elsevier Science Ltd. All rights reserved.