The effects of operating conditions on boron removal from geothermal waters by membrane processes

The main objective of this work was to determine the optimum operating conditions for boron removal and permeate flux in geothermal waters employing lab-scale tests. A total of 8 different SWRO, BWRO and NF membranes were tested. Permeate boron concentrations as low as 1.0 mg/L were obtained by the BWRO membranes at 20.7 bar (300 psi) pressure and pH 8.0. Using SWRO membranes, permeate boron concentrations of about 0.3-0.7 mg/L were obtained at 48.2 bar (700 psi) pressure and pH 8.0. Increasing pH from 8 to 10.5 significantly increased boron rejections by all membranes. At pH 10.5, permeate boron concentrations as low as 0.04 mg/L were obtained by BWRO membranes. However, at pH 10.5, higher degree of flux reductions was observed due to enhanced scaling. Tested BWRO and SWRO membranes were effective in rejecting silica, sulfate and conductivity. No correlation among boron and salt rejections was found. Results suggested that tested geothermal water may be effectively desalinated by BWRO membranes and used for various types of agricultural irrigation. Such approach may not only provide irrigation water but also may reduce the negative impacts of discharged brackish geothermal waters after use to the receiving water bodies and surrounding agricultural areas.