Desalination of Brackish Water Using Reverse Osmosis

Abstract

Pakistan is among the 36 most water stressed countries and facing water scarcity problem. Desalination of brackish water using reverse osmosis is a common practice now a days adopted for fresh water supply. In reverse osmosis, the sustainability of the process is mainly based on pre-treatment and its membrane performance. This study aims to compare at pilot scale the rejection efficiency of RO membranes with different pretreatment options at different transmembrane pressures and TDS conditions. In this study, synthetic brackish water was prepared and performance evaluation was carried out using brackish water reverse osmosis (BWRO) membranes preceded by different pre-treatment technologies including 5 and 1 μm cartridge filters, Ultra-filtration (UF) having 0.02 μm pore size, and forward osmosis (FO) using 0.25 M NaCl and MgCl2 as draw solution (DS) to avoid membrane fouling and improve process performance. Two commercial membranes, Filmtec Lc-Le-4040 and Hydranautics-CPA5-LD-4040 were also compared in parallel. Our results revealed that cellulose tri-acetate forward osmosis membrane preceded by polyamide filmtech lc-le-400 membrane with 0.25 M MgCl2 used as a draw solution gave overall 97% rejection with less fouling characteristics. Ultra-filtration (UF) membrane preceded by both filmtech lc-le-4040 and hydranautics cpa5-ld-4040 membrane also found effective and gave 98 and 96% rejection but having fouling potential to UF membrane due to high pressure application and for RO membrane due to presence of other ionic compounds. 5 & 1 μm melt blown cartridge filter prior to RO membrane also showed effective results with both membrane