Development of high-integrity reverse osmosis membranes for enhanced removal of microorganisms

Improved integrity of reverse osmosis (RO) membranes for pathogenic microorganisms can enhance the microbiological safety of potable water reuse. This study aimed to produce a high-integrity RO membrane that is less prone to defects or failures of the polyamide skin layer. The commercial track-etched (TE) microfiltration membranes with uniform pore sizes of 0.2 mu m were adopted as a robust support layer. The polyamide skin layer was successfully formed by creating a thin m-phenylenediamine (MPD) layer using a spin coater before the interfacial polymerization. The best TE-based RO membranes had a pure water permeability of 1.1 L/m2hbar and a salt rejection of 97 %. The field emission scanning electron microscopy revealed that the skin layer thickness of the TE-based membrane (approx. 31 nm) was equivalent to a commercial RO membrane. The removal of bacteria-sized particles (0.5 mu m fluorescent microspheres) by the fabricated TE-based membrane (8.6-log) was greater than that by the commercial RO membrane taken out from an RO membrane element (7.8-log). Although complete removal of bacteria-sized particles was not achieved with small TE-based RO membrane coupons, this study established a viable protocol for producing a high-integrity RO membrane by forming the polyamide skin layer on the TE support layer.