Removal of boron in a multistage SWRO system with pre-crystallization

Recently, the desalination facilities use the membrane method that it is more effective and economical than the thermal method. And, the most recent a multistage seawater reverse osmosis (SWRO) system has been applied to increase the recovery rate. A multistage SWRO system has some more economical advantages for desalination than a single-stage SWRO system, such as high recovery rate, reuse of the brine pressure, and decreased brine quantity. However, there is still a problem related to the boron concentration exceeding drinking water quality standard. Therefore, the purpose of this study was to discuss the removal of boron using a multistage SWRO system with pre-crystallization for the removal of scale-causing substances and to change the form of boron. As a result, the boron concentration in permeate of the second stage-SWRO membrane in the pre-crystallization process (permeate (2)) was 0.48 mg/L, and that via the conventional process was 2.87 mg/L. And, the recovery rate of the experiment that applied pre-crystallization process was observed to be higher than that of the conventional process at the same operating pressure. The pH of the permeate (2) was weakly basic, at 8.53; therefore, it was concluded that the pH control process could be omitted from the post-treatment.