The Improvement of Perm-selectivity Prediction of Forward Osmosis: Modeling and Experimental Analysis

Abstract

Perm-selectivity consisting water flux Jw and solute flux Js or in the form of Js/Jw ratio are an important parameter of designing Forward Osmosis (FO) membrane as it indicates the membrane performance and how much solute replenishment over extracted pure water from the feed solution. Parameter Js/Jw ratio is dependent of hydrodynamic condition i.e cross-flow velocity, solute type i.e. diffusivity, trans-membrane surface potential effected by membrane surface charge. This study deployed Cellulose Triacetate (CTA) membrane for representing low-charge membrane and Polyamide-Thin Film Composite (PA-TFC) for membrane of high surface charge. Six (6) different models were used to pin-point the effect of external mass transfer, the ideal solution, non-ideal solution, Donnan potential (trans-membrane surface potential) on the transport of solute across the membrane. Our models exhibit the best prediction towards perm-selectivity. In low surface charge membrane i.e. CTA, underlying transport mechanism was diffusion. While, in high surface charge membrane i.e. TFC, incorporation of trans-membrane surface potential shows partition of solute to be the governing mechanism trough Donnan potential. Improvement with experimental mass transfer for external boundary provide better and more reasonable prediction of effective A, B, and S parameter for FO membrane.