Comparative performance of FO-RO hybrid and two-pass SWRO desalination processes: Boron removal

The boron removal and behavior in seawater forward osmosis (SWFO) and seawater reverse osmosis (SWRO) were evaluated under various operating conditions. Similar trends in boron removal for both SWFO and SWRO were observed: boron removal increased as the feed solution/water pH increased. In addition, the optimal operating conditions for the SWFO as a pretreatment step for SWRO were investigated considering the boron concentration in the diluted draw solution and the dilution rate. When the boron and NaCl concentrations were 2 mg/L and 24,000 mg/L in the SWFO diluted draw solution, the boron concentration in the permeate was 0.4 mg/L for the SWFO-SWRO hybrid process. Therefore, the SWFO-SWRO hybrid process did not require any pH adjustment, whereas the two-pass SWRO required a pH adjustment to 11 in the second SWRO in order to remove boron, which affects the economic feasibility, such as the operating expenditure. Thus, the SWFO-SWRO hybrid process can save the 19,200,000 $/yr than the two-pass SWRO because it is an economical and efficient process in pH adjustment or dilution aspects compared to the two-pass SWRO process.