Desalination of high salinity brackish water low pressure reverse osmosis

Abstract

Most of the hitherto reported applications of low pressure reverse osmosis membranes have been concerned with pilot scale or small size test situations involving feed waters with relatively low levels of dissolved solids (less than 2000 mg/l), with resulting net driving pressures of 14–15 bar (ca. 200 psi) or more. This paper describes the results obtained for thousands of hours of still continuing operation, of a much larger plant currently producing at least 3000 m 3/d (ca. 0.8 MGD) of product. The feed in this case has a dissolved solids content of 6,000–6,500 mg/l at 65% recovery at a feed pressure of less than 14 bar (ca. 195 psi) with a system net driving pressure of no more than 7 bar (95–100 psi). Even though the feed has a significant monovalent ion content, the permeate TDS is less than 3000 mg/l. The power consumption, using existing pumps, piping, and circuitry is only slightly more than 1 kWh/m 3 of product (less than 4 kWh/kgal). Plant performance has been and continues to be level with respect to all parameters including intrinsic productivity, salt passage, differential pressures, etc. It is being monitored, analyzed, and evaluated using specially developed computer software and the results will be shown in this paper. On the basis of the excellent stable results achieved to date with these newly commercial membranes and elements on a large scale, a number of further performance and cost improvements are being considered for early implementation.