Improved performance of reverse osmosis with dynamic layers onto membranes in separation of concentrated salt solutions

Improving the salt rejection of reverse osmosis (RO) membranes of MHA types (`Polymersintezʹ, Russia) in separation of concentrated sodium sulphate solutions, using dynamic-layer-forming polymers as additives into the solutions to be filtered has been studied. It has been shown that, unlike coagulating polymers, a non-coagulating polymer (NCP) or a hydrophylized coagulating polymer (HCP) can be effective as a rejection enhancing additive at a high salt concentration. For the membranes coated by the NCP or HCP dynamic layer, the salt rejection is invariable or slightly decreases with the increase of the Na2SO4 concentration up to 50 g/l, whereas for the uncoated membranes the salt rejection decreases sharply under the same conditions. The improvement of the rejection characteristics occurs without any or significant loss in the membrane water flux. In contrast to the clean membranes, the coated membranes display the high, similar to maximum, salt rejection at the relatively low pressure 2¯3 MPa, but the flux increases almost linearly with pressure. The influence of the cross-flow velocity and concentration of the polymer additive on the membrane performances has been examined.