NAMS 2002 Workshop - ICOM 2008

Membrane Fouling IV - RO & Desalination – 3
Friday July 18, 10:45 AM-11:15 AM, Moloka’i
The Effect of Membrane Body Conductance on the Zeta Potential of Clean
and Fouled Polymer Membranes
T. Luxbacher (Speaker), Anton Paar GmbH, Austria - thomas.luxbacher@anton-paar.com
A. Comerton, University of Toronto, Toronto, Canada
R. Andrews, University of Toronto, Toronto, Canada
D. Bagley, University of Wyoming, Laramie, Wyoming, USA
The electrokinetic or zeta potential is an important property of charged solidliquid
interfaces and provides insight regarding the charging behaviour of solid
surfaces and colloidal particles immersed in a dielectric. Experimental methods
to determine the zeta potential include streaming potential, electrophoresis, or
electroacoustic techniques. The streaming potential method has become a
common tool to determine the zeta potential of macroscopic solid surfaces of
granular or fibrous substances as well as flat sheets. The application of the
streaming potential to the characterization of thin-film composite membranes for
water treatment is widely known. Beside the characterization of the active
membrane surface, the streaming potential gives information about the
interaction between the membrane and ions, organics, and surfactants, which
provides useful insights into the relationship between reverse osmosis (RO) and
nanofiltration (NF) membrane surface properties, separation performance and
membrane fouling.
Despite of the acceptance of the streaming potential method in the field of
membrane surface characterization, the effect of the electrical conductivity of the
membrane bulk on the charging behaviour of the membrane surface is often
underestimated. The streaming potential measurement is sensitive to surface
conductivity, which is likely to occur on NF and RO membranes, and allows the
determination of an apparent zeta potential only. In this paper we compare the
calculated zeta potential of commercial NF and RO membranes determined from
streaming potential measurements to that calculated from streaming current
results. The streaming current measurement is insensitive to effects like surface
conductivity or membrane body conductance and reveals the complete zeta
potential information. We extend the comparison of virgin membranes to NF and
RO membranes fouled with different sources for drinking water. The effect of
membrane fouling on the surface chemistry is monitored by the streaming current
measurement whereas the ratio between the apparent zeta potential and the
correct value is affected by the change in the membrane porosity.