Relating Water/Solute Permeability Coefficients to the Performance of Thin-Film Nanofiber Composite Forward Osmosis Membrane

Abstract

The thin-film nanofiber composite (TNC) forward osmosis (FO) membranes are fabricated and systematically modified by a series of post treatments, such as adding additives into the monomer, NaOH treatment, chlorine treatment and support modification. The post treatments lead to the formation of modified membranes with a wide range of water permeability (A) and solute permeability (B) values. The impact of varied A, B and B/A values on the FO performance are systematically investigated. Furthermore, the value of B/A is related to internal concentration polarization (ICP), external concentration polarization (ECP) and solute leakage, which are firstly proposed in this study. Compared with the Pressure Retarded Osmosis (PRO) orientation (i.e., active layer facing draw solution), the water flux is much lower at FO orientation (i.e., active layer facing feed solution) due to severe loss of effective osmotic pressure, which mainly results from the convective dilution and low mass transfer coefficient in support membrane (i.e., the D/S value). In addition to this, the coupled effect of solute leakage and low D/S value also causes a minor loss of effective osmotic pressure. This is the first study to systematically analyze the B-A relationship of TNC membranes employing different modification techniques and to investigate the impact on the FO performance.