Impacts of silica on the sustainable productivity of reverse osmosis membranes treating low-salinity brackish groundwater

Abstract

Brackish water desalination is increasingly being considered as an alternative drinking water treatment processes. The impacts of high silica (63 mg/L) on the performance of brackish water reverse osmosis (BWRO) while treating a brackish groundwater (1315 mg/L of TDS) were investigated. This study demonstrated the importance of pilot-scale testing in understanding the long-term impacts of silica fouling in order to maintain the sustainable flux and recovery of new generation BWRO membranes. Two commercial membranes, selected from bench-scale coupon testing, were evaluated at pilot scale. The results suggested that due to the presence of high silica, operational flux and recovery were limited to 16.9 Lm − 2 h − 1 and 75%, respectively, for both RO membranes. The silica fouling predominantly occurred in the second stage of the RO systems, and membrane autopsy revealed that the foulant layer was primarily comprised of inorganic elements (10% organic, 90% inorganic) including silicon and a small amount of aluminium. The antiscalant and chemical cleaning were essential to minimize silica scaling and to restore flux; however, the flux decline rates were faster in the subsequent cycles indicating the detrimental effects of silica deposition. The annual chemical cost could be significantly high due to the increased frequency of chemical cleaning.