Influence of physicochemical characteristics of feed solution on water permeability in forward osmosis desalination system

Abstract

Many chemical species are involved in the feed solution (FS) in a forward osmosis (FO) process used for water/wastewater treatment and desalination. Chemicals and their molecular interactions in FS could have variable influences on water transfer and permeability, and consequently the overall performance of the FO process. This fundamental is important for understanding molecular transfer mechanisms in FO system, but has received a little attention. This preliminary study associated with its systematic investigations aimed to discover the impacts of physical and chemical properties (chemical composition, diffusivity, molar mass and charges) of FS on the water transfer characteristics and permeability in a FO desalination system. We evaluated the water flux in FS containing different salts in natural water and seawater. Our results revealed that water permeability can be significantly affected by the chemical constituents and molecular weights of FS. Water flux profiles follow an order of cations in FS: Na+ > K+ > Mg2+ > Ca2+, while high water flux reduction was found in K+ and NO3− FS. Solute diffusivity in FS was evidenced to play a crucial role in the water permeability. High water flux was determined in the FS with K+ and NO3− as which have the high diffusion coefficient. Experimental data showed that water flux could be affected by ionic mass and charge of solutes in FS as analysed by ratio of charge to molar mass (Z/M). Water flux reduction follows an increase of Z/M. This preliminary study raises insight to getting better understanding of molecular interactions in the chemically complex FS and their impact on the water transfer mechanisms in FO system.