MEMBRANE SELECTION CRITERIA FOR SEAWATER DESALINATION BY REVERSE OSMOSIS

Abstract

Seawater desalination is a technology with a high-speed evolution for obtaining drinking water from seawater, especially in vulnerable areas of the globe. Reverse osmosis is the most used technology and is supported by the commercial development of many types of membranes widely used in desalination. However, there are no general rules for membrane selection. A single criterion is generally accepted: the membrane's permeability to the salts in the feed (generally to sodium chloride). This article has three specific aims: 1) experimental determination of the salt content of the water of four selected seas (i.e., Paralia Katerini - Greece, Civitavecchia - Italy, Tunis – Tunisia, and Manifah - Saudi Arabia). 2) from an extensive range of commercially available membranes, after consulting several "technical data sheets", four types of membranes were selected for this study: Hydranautics SWC6 - LD, Koch TFC - HF - 8", Toray TM820V - 400. Our calculation regarding their permeabilities led to values in the range of 0.61 liter/m2·h·bar to 1.87 liter/m2·h·bar. 3) for each selected membrane, the total area required in a RO plant to obtain a permeate flow of 1 000 m3/day and a salt concentration in the permeate of 225 ppm was calculated for an operating pressure in the range of 35 bar to 65 bar, for operating temperature in the range of 20°C to 50°C and for seawater salinity in RO feed in the range of 30 000 ppm to 50 000 ppm. The concentration of salts in the feed and the operating pressure have the most significant influence on the increase in the total area of the membranes in the reverse osmosis plant.