MEASURING THE ZETA (ELECTROKINETIC) POTENTIAL OF REVERSE-OSMOSIS MEMBRANES BY A STREAMING POTENTIAL ANALYZER

The use of a novel streaming potential analyzer to measure the zeta po tential of cellulose acetate and composite polyamide reverse osmosis m embranes is reported. Zeta potentials of these membranes were measured at various solution chemistries. These include effects of salt (NaCl) concentration, solution pH, and the presence of dissolved humic subst ances. It is demonstrated that streaming potential is a useful tool to measure zeta potential of reverse osmosis membrane surfaces. Results indicate that solution chemistry has a marked effect on the electrokin etic properties of reverse osmosis membranes. Humic substances strongl y adsorb onto the surface of reverse osmosis membranes and thus alter the surface charge of the membranes. Furthermore, the zeta potential o f reverse osmosis membranes becomes more negative as the NaCl concentr ation in solution increases, in a marked contrast to conventional elec tric double layer theories. It appears that the zeta potential of reve rse osmosis membranes is strongly influenced by the presence of unreac ted chemical substances or impurities on the membrane surface. Various explanations for the behavior of the membranes at the above solution chemistries are evaluated and discussed.