NAMS 2002 Workshop - ICOM 2008

Hybrid and Novel Processes II – 2
Thursday July 17, 3:00 PM-3:30 PM, Kaua’i
Nanoparticle-Enhanced Microfiltration for Low Energy Metal Removal from
Water.
A. Jawor (Speaker), University Of California Los Angeles, Los Angeles, California, USA -
ajawor@ucla.edu
E. Hoek, University Of California Los Angeles, Los Angeles, California, USA
Polymer-enhanced ultrafiltration (PEUF) is highly effective for selectively
removing metal ions from water, but this process is difficult to implement in
practice because polymer gel formation and pore plugging lead to severe, often
irreversible flux decline. Recently, dendritic polymers (a.k.a., dendrimers) have
been proposed as a high-binding capacity, low-fouling alternative to traditional
polyelectrolytes. However, dendrimers are very expensive and require use of
tight, ultrafiltration membranes. Nanoparticle-enhanced microfiltration (NEMF) is
a hybrid membrane process, like PEUF, where a target contaminant selectively
reacts with nanoparticles added to a mixed reactor. Contaminant-nanoparticle
complexes are removed using low-pressure microfiltration membranes.
In this study, we evaluate nanoparticle-enhanced microfiltration using inorganic
nanoparticles. Our objective is to demonstrate selective removal of divalent metal
cations from simple and complex electrolytes through addition of metal-binding
nanoparticles followed by microfiltration. As a first step towards testing this
concept, we evaluate a traditional polyelectrolyte (polyacrylic acid), a succinic
and carboxylic acid functionalized PAMAM dendrimers, and a NaA zeolite
nanocrystals as metal-binding agents in combination with various microfiltration
and ultrafiltration membranes. Electron microscopy, light scattering, particle
electrophoresis, direct titrations, and contact angle analyses are used to
characterize nanoparticle size, shape, hydrodynamic radius, zeta potential,
charge density, and surface energy, respectively. Preliminary metal-binding
experiments are performed to elucidate nanoparticle binding kinetics, capacity
and strength (i.e., reversibility) using various divalent metal ions (Ca 2+ , Mg 2+ ,
Ba 2+ , Sr 2+ , Cd 2+ ). Nanoparticle rejections and flux decline are determined using
polysulfone- based UF and MF membranes ranging from molecular weight cut-off
(MWCO) of 5 kD up to a characteristic pore size of 100 nm. Mechanisms of
membrane fouling by polymers, dendrimers, and nanocrystals are elucidated by
fitting flux decline data with classical blocking filtration models. Clean and fouled
membrane surfaces are analyzed by SEM/EDX to confirm morphology and
composition of fouling layers formed. Additional membrane characterization
includes pure water permeability and zeta potential by electrolyte filtration
experiments, plus surface roughness and energy via AFM and contact angle
analyses.