Boron transport through polyamide-based thin film composite forward osmosis membranes

Abstract

The boron transport in forward osmosis (FO) process using thin film composite (TFC) membranes has been investigated. Two common fertilizers were used as draw solutes and a model seawater as the feed. The influence of several physical and chemical operating conditions on boron solute flux and boron rejection rates was investigated. The examined factors include draw solution types, membrane orientation, feed and draw solution concentrations, boron feed concentration, crossflow rate, and feed solution pH. The key mechanisms that govern boron transports are reverse draw solute flux and internal concentration polarization experienced by the membrane during the FO process. Results show that the use of draw solute with small hydrated radius could improve boron rejection hindered by the higher reverse diffusion of draw solutes. The osmotic process operated in the pressure retarded osmosis (PRO) mode results in lower boron rejection. However, the most effective boron removal was achieved by operating the feed solution at high pH (pH=11) because boron in the solution contains larger-size borate species, and thus increases boron rejection rate up to 94% by electrostatic repulsion. This study mainly focused on the performance of TFC membrane in boron removal.