NAMS 2002 Workshop - ICOM 2008

forward osmosis, the RO process is thus protected from scaling and fouling of
any constituents present in the source of impaired water.
An important caveat of the forward osmosis process is that its membrane, like all
synthetic semi-permeable membranes, is not perfectly selective. Sparingly
soluble solutes, toxic metals, and other emerging contaminants of concern
present in the feed solution, as well as the draw solution solutes, will inevitably
diffuse across the forward osmosis membrane. The introduction of sparingly
soluble solutes into the final RO stage may subsequently scale the RO
membrane, while the diffusion of draw solution solutes against flow of water
represents inefficiency in the system because lost solutes will have to be
replenished. Despite the multi-barrier treatment obtained by such a system, there
is still concern that toxic metals and other containments of interest will cross both
the forward osmosis and RO membranes and contaminate the product stream.
In the current study, multiple tests were performed to elucidate the diffusion of
solutes across two different cellulose triacetate forward osmosis membranes.
These studies were performed with the aid of a novel supervisory control and
data acquisition (SCADA) system developed by the authors. Using the SCADA
system, the authors were able to conduct experiments at very steady conditions
including constant temperatures, flux, and draw solution concentrations. These
studies utilized feed solutions containing both single salts and synthetic brackish
water to characterize specific and competitive solute diffusion through the
forward osmosis membranes. Samples from these experiments were analyzed
by ion chromatography (IC) and inductively coupled plasma (ICP) to determine
solute transport across the membranes. Data collected from this analysis was
used to determine the individual solute’s permeation tendency through the
membrane.