NAMS 2002 Workshop - ICOM 2008

Membrane and Surface Modification II – 4
Thursday July 17, 4:00 PM-4:30 PM, O’ahu/Waialua
High Performance Surface Nano-Structured RO/NF Membranes
G. Lewis, University of California, Los Angeles, California, USA
N. Lin (Speaker), University of California, Los Angeles, California, USA
M. Kim, University of California, Los Angeles, California, USA
Y. Cohen, University of California, Los Angeles, California, USA - yoram@ucla.edu
Reverse Osmosis (RO) and Nanofiltration (NF) membranes used for surface and
groundwater desalination are susceptible to bio-organic fouling (i.e., proteins,
humic acid, fulvic acid), colloidal fouling and mineral salt scaling. Membrane
fouling and/or scaling not only results in a decreased membrane permeate flux
but also protein adhesion and mineral salt scale formation that may permanently
alter the physical features of the surface and lead to irreparable membrane
damage. Previous strategies for mitigating membrane fouling/scaling (i.e.,
polymer surface adsorption and UV, gamma irradiation, and low-pressure plasma
graft polymerization) have relied on alteration of the membrane surface chemistry
and topography by addition of a permselective polymer thin film that would act
both as a separation layer and a physical boundary to prevent adsorption of
organic and mineral salt species. In the present study, a novel atmospheric
pressure plasma-induced graft polymerization method was developed to enable
the generation of a high surface density of active surface sites for subsequent
graft polymerization using a suitable monomer. Surface graft polymerization was
then carried out to form a dense layer of grafted polymer chains that are
covalently and terminally bound to the surface. The chemical and physical
features of the resulting grafted polymer film may be tuned by altering the
monomer chemistry as well as the reaction conditions to achieve unique
architectures for effective advanced materials in membrane separations.
Using the above approach of atmospheric pressure plasma-induced graft
polymerization (APPIGP), a novel class of RO and NF membranes were
developed. Characterization of membrane bio-organic fouling studies were
conducted in a dilute aqueous feed stream of model proteins. Surface scaling
was evaluated by subjecting the surface structured membranes to a dilute
aqueous mineral salt solution with the onset of mineral scaling detected by a
novel scale-observation imaging system. The properties of the grafted polymer
on the RO and NF membranes, specifically the surface density, polymer chain
length, and monomer chemistry, were evaluated with respect to the membrane
performance (i.e., onset of mineral scaling, water permeate flux decline and
surface scale coverage) to determine the optimal surface structuring conditions
required reduce surface fouling/scaling. The properties of the grafted surfaces,
such as surface topology and surface feature uniformity, were evaluated by