Theory

Abstract

Various reviews (Pusch 1986;Soltanieh and Gill 1981;Mazid 1984;Dickson 1988;Dresner and Johnson 1980;Jonsson 1980;Rautenbach and Albrecht 1989; and Sourirajan and Matsuura 1985) on reverse osmosis (RO) transport mechanisms and models have been reported in the literature. Several models have been developed to describe solute and solvent fluxes through RO membranes. The transport models can be divided into three types: nonporous or homogeneous membrane models (solution-diffusion, extended solution-diffusion, and solution-diffusion-imperfection models), pore-based models (preferential sorption—capillary flow, finely porous, and surface force—pore flow models), and irreversible thermodynamics phenomenological models (such as KedemKatchalsky and Spiegler-Kedem models). Most models for reverse osmosis membranes assume diffusion or pore flow through the membrane while charged membrane theories include electrostatic effects. A model that includes prediction of reverse osmosis rejection to multi-ionic salt solutions was reported by Brusilovsky and Hasson (1989). For nanofiltration membranes, which are often negatively charged, Donnan exclusion models and the extended Nernst-Planck model can be used to determine solute fluxes.