Effects of substrate (track-etched filter) properties on the performance of forward osmosis membranes

Highly permeable membranes can improve the validity of water treatment using forward osmosis (FO) membranes. This study aims to identify the effects of substrate (track-etched (TE) filter) properties on the permeability of FO membranes. The polyamide active layer properties of three types of TE filters with similarly-sized pore diameters (0.2 μm) were observed to be equivalent regardless of the substrate porosity (13.7%–15.8%) and substrate thickness (10–25 μm). Under the same fabrication protocol using 1.5 wt% m-phenylenediamine (MPD) solution with 0.25 wt% sodium dodecyl sulfate (SDS) addition, the increased porosity of the TE filter increased water flux. This suggested that further reduction in thickness and increase in porosity can enhance the water flux. The addition of SDS to an MPD solution was crucial in maximizing the water flux of TE filter-based FO membranes, and the other approaches (no surfactant addition or the addition of Tween80 or hexadecyltrimethylammonium bromide) produced lower water flux. The optimized fabrication protocol presented the highest water flux of 43 L/m2h and reverse salt flux of 10 g/m2h with the draw (1.0 M NaCl) and feed (pure water) solutions. This study determined the best approach for forming a highly permeable PA active layer on TE filters.