NAMS 2002 Workshop - ICOM 2008

Membrane Fouling III - RO & Biofouling – 4
Thursday July 17, 4:00 PM-4:30 PM, Maui
Role of Seawater Chemistry in Algal Biopolymer Fouling of Seawater RO
Membranes
X. Jin (Speaker), University of California Los Angeles, Los Angeles, California, USA -
jinxuesky@ucla.edu
E. Hoek, University of California Los Angeles, Los Angeles, California, USA
A major fouling concern in seawater reverse osmosis (SWRO) plants is the
increased biomass generated during algal blooms. Algae, bacteria, and their
exudates are present in high concentrations, and thus, have the potential to foul
RO membranes. Although, membrane fouling by colloids and dissolved organics
has been studied extensively for brackish and wastewater applications, fouling
behavior may be very different in seawater due to the high ionic strength and
suppression of electrical double layer interactions. We hypothesize that short-
range interfacial interactions will play a critical role in determining the rate and
extent of SWRO membrane fouling and that seawater chemistry will strongly
impact foulant-membrane interfacial interactions. As a first step towards
understanding the role of seawater chemistry in SWRO membrane fouling, we
have conducted a study of SWRO membrane fouling by algal biopolymers.
Commercially available SWRO membranes - FilmTec SWHR (Dow Chemicals,
Minneapolis, MN) and SWC3+ (Hydranautics, Oceanside, CA) - are used as
model SWRO membranes. The two membranes were selected because they
represent a relatively hydrophobic, rough membrane with significant carboxylic
acid functionality at its interface (Hydranautics SWC3+) and a relatively
hydrophilic, smooth membrane with relatively little carboxylic acid functionality at
its interface (FilmTec SWHR). The former is expected to be more fouling prone
due to attractive acid-base interactions and its rough, carboxylic acid rich
interface. The latter membrane is expected to be relatively resistant to fouling
due to repulsive acid-base interactions and its relatively smooth, non-
carboxylated interface.
Accelerated fouling experiments are carried out in a bench-scale SWRO
simulator with 6 parallel flat-sheet membrane cells. Alginic acid - an acidic
hetero-polysaccharide excreted by Brown algae - is spiked into synthetic
seawater solutions with constant total dissolved solid (TDS) concentrations of 32
g/L, but varied concentrations of major cations (e.g., sodium, magnesium,
calcium). In addition, a real seawater matrix (Instant Ocean®) was also
evaluated. Water flux and conductivity rejection are tracked with time. At the end
of fouling experiments, cleaning is performed first using laboratory de-ionized
(DI) water, followed by a 5 mM EDTA solution adjusted to pH 11 by NaOH