ABSTRACT
Hollow fiber membranes are less convenient for food
applications because of extensive fouling and difficult
cleaning.
MASS TRANSFER IN RO
Mechanism of Solvent and Solute Transport
Unlike ultrafiltration and microfiltration membranes, RO
membranes are, at least at their barrier skin layer, essen-
tially non-porous. Thus, solvent flux and solute rejection at
the barrier surface cannot be satisfactorily explained solely
in terms of transport through pores and capillaries.
Different theories have been proposed to explain and pre-
dict solute and solvent transport through RO membranes.
The homogeneous solution-diffusion (HSD) model, pro-
posed by Lonsdale, Merten, and Riley[6] assumes that both
the solvent and the solute dissolve on the homogeneous
(poreless) surface layer and then travel through the mem-
brane by molecular diffusion. Separation is explained in
the light of differences in the solubilities and diffusivities
of the solvent and solute. Other variants of this model
assume a combination of molecular diffusion and pore
flow. The preferential sorption-capillary flow model
(PSCF), proposed by Sourirajan[7] assumes that the mem-
brane surface is essentially microporous. If the membrane
material has preferential sorption for water and negative
sorption (repulsion) for salt, then a monomolecular layer of
pure water separates at the interface and is forced into the
micropores. Another model, based on irreversible thermo-
dynamics theory, was proposed by Kedem and
Katchalsky.[8] An extensive review of theories relevant
to mass transport in RO has been provided by Soltanieh
