New thin-film composite low pressure reverse osmosis membranes and spiral wound modules

Abstract

This paper describes improved thin-film composite low pressure reverse osmosis membranes developed by Nitto Electric Industrial Company. These membranes exhibit high salt rejection and high permeate flux at low operating pressures, combined with good chlorine resistance and thermal stability. The characteristics of the two new membrane types, the NTR-739HF and the NTR-729HF, both available as spiral-wound modules, are discussed in detail. The NTR-739HF exhibits up to 95% salt rejection at a flux over 0.8 m 3/m 2d (20 gfd), when tested at 1 MPa (143 psi) and 25°C (77°F) on 1500 ppm NaCl solution. The NTR-729HF has a water flux greater than 1.3 m 3/m 2d (32 gfd) and a salt rejection above 92% when tested in the same conditions. In actual module trials with brackish water, salt rejections of 96% (product water = 60 ppm TDS) have been obtained. The membranes are stable to chlorine in feed water, as shown by long-term reverse osmosis tests with tap water containing about 1 ppm residual chlorine.