A novel energy-efficient concurrent desalination and boron removal (CDBR) process

Seawater desalination provides water for many uses including irrigation. A concern is to remove boron in seawater whose concentration can reach 10 ppm. Boron is required for plants but becomes toxic between 0.5 and 10 ppm for many crops. Since boron in seawater appears as boric acid, the boron rejection of RO membranes is ≤ 90%. Hence, conventional RO requires a two-pass process to reduce the boron adequately but with limited water recovery. Desalination and boron removal can be done via multi-step processes using pH adjustment, ion exchange, adsorption and electrodialysis that involve increased complexity and cost. A concurrent desalination and boron removal (CDBR) process is described and modeled that employs only membrane technology. For seawater containing 10 ppm of boron and 35,000 ppm of salt, the CDBR process can produce water containing 0.5 ppm of boron and < 100 ppm of salt with a water recovery of 65% at an osmotic pressure differential of 56.6 bar and net specific energy consumption of 2.70 kWh/m³. The CDBR process can be retrofit onto existing desalination plants and can produce a concentrated brine that can be used in a hybrid CDBR-PRO (pressure-retarded osmosis) process to harvest its osmotic potential energy.