Reverse osmosis seawater desalination: current status of membrane systems

Reverse osmosis is currently the most important and commonly used desalination technique. The objective of this paper is to review the history of reverse osmosis membranes, to outline the current state of the art and insight into the tendencies being. The current market of RO membranes is focused on thin-film composite polyamide membranes, which are made of three layers and with an average molecular weight cut-off of 100–150 Da in order to obtain a high salt rejection. Until reaching current RO membranes, there have been numerous developments, highlighting the development of NS-100 membranes by Cadotte in 1977 and subsequent optimization of the manufacturing conditions. Other improvements were surface modification and membrane post-treatment actions. The most common configuration used in desalination plants are polyamide spiral wound membranes (SWM), which involves several flat sheet membranes that are glued together pairwise on three sides with the fourth side left open. The membrane elements are connected in series using interconnectors and installed into a pressure vessel. Current research regarding SWM is focused on providing greater surface area within the same volume. Another point of interest is to achieve a high retention of boron to comply with current legislation.