Efficient brine concentration of highly saline and hypersaline water using forward osmosis: A modeling study

Treating highly saline water (TDS of less than 35 g/L) and hypersaline water (TDS of more than 70 g/L) are some of the pressing challenges in wastewater treatment. Brine concentration is one of the significant steps in wastewater treatment to reduce the volume of the brine. This study aims to investigate the performance of a forward osmosis (FO) system for concentrating the brine (highly saline and hypersaline water) by a novel alcohol-based draw solution (isopropanol) for the very first time (owing to its high osmotic pressure, drawability, and solubility) and membrane advancement (biomimetic-based hollow fiber forward osmosis membrane). The osmotic pressures of draw solutions (DSs) were obtained experimentally by vapor pressure osmometry, which was then fed as an input to the FO model (i.e., a solution-diffusion model in MATLAB). Furthermore, regeneration of DS was achieved using extractive distillation modeling in Aspen Plus V14. Results reveal that concerning highly saline water, a water flux of 16.24 LMH and a recovery of nearly 61% were achieved with a minimum specific reverse solute flux (SRSF) of 4.1 g/L. Similarly, with hypersaline water, a water flux of 12.41 LMH and a recovery of 52.4% were achieved with a minimum SRSF of 3.8 g/L. The diluted DS (50% isopropanol) was further regenerated to produce pure water (0.2 ppm isopropanol) and regenerated DS (for reuse in FO). Hence, the isopropanol-based draw solution is recommended for concentrating the industrial and hypersaline water, thereby achieving Sustainable Development Goal 6: Clean Water and Sanitation, developed by the United Nations.