Osmotically assisted reverse osmosis for high salinity brine treatment

This work evaluates a novel osmotically assisted reverse osmosis (OARO) process for dewatering high salinity brines using readily available membranes and equipment. While traditional reverse osmosis processes are limited to treating brines with osmotic pressures below the membrane burst pressure, in OARO, the osmotic pressure difference across a membrane is reduced with a permeate side saline sweep. A series of OARO stages can be used to sequentially reduce the concentration of the feed until a traditional RO process can obtain fully desalinated water. This paper develops an OARO model to identify feasible operating conditions for this process and to estimate the water recovery and energy consumption across a range of brine feed concentrations. For a feed of 100-140 g/L sodium chloride, we estimate that the OARO process is capable of a 35-50% water recovery with an energy consumption of 6-19 kWh per m3 of product water. The results suggest that an OARO dewatering process improves upon the recovery of reverse osmosis for high salinity brines and has a comparable or lower energy consumption than mechanical vapor compression.