(613c) Single-Stage Osmotically Assisted Reverse Osmosis for the Treatment of Hypersaline Brine

The high osmotic pressures of hypersaline brines make it not feasible to be treated with conventional reverse osmosis (RO) membranes, as their osmotic pressures tend to exceed the membrane burst pressure. These solutions are therefore discharged into water bodies, which pose a threat to aquatic life due to high salinity at the point of discharge. Osmotically Assisted Reverse Osmosis (OARO) is a water desalination technique aimed at treating hypersaline brines with conventional RO membranes. The OARO setup makes it possible to treat such systems without compromising membrane performance due to the step-down in the feed osmotic pressure. However, the multiple stages involved make the system both energy- and capital-intensive and, hence, not economically viable. In this work, we propose a Single-Stage Osmotically Assisted Reverse Osmosis (SSOARO) technique, which is a modified approach to the OARO process. This method makes it feasible to treat hypersaline solutions in a single setup to minimize the energy and capital demand while improving the pure water recovery of the feed. In the presence of a membrane-encapsulated draw solute, we were able to reduce the osmotic pressure of the system and hence operate the system at suitable pressures well below the burst pressure of the RO membrane. With a hypersaline feed of 1.54 M NaCl operating at 70 bar, we realize a salt rejection of 80% with a flux of 2.3 Lm^-2h^-1. Meanwhile, a single RO membrane operating at this concentration and pressure exhibits a 74% salt rejection with a corresponding flux of 2.2 Lm^-2h^-1. The comparable flux and NaCl rejection from both systems lead us to further investigate the possible factors influencing them. Accordingly, we probe further into the effects of both diffusive and advective transport modes, which tend to dominate at different points within the membrane and at different conditions of pressure, temperature, and concentration.