Osmotically assisted reverse osmosis (OARO): Five approaches to dewatering saline brines using pressure-driven membrane processes

The ability of osmotically assisted reverse osmosis to draw water from concentrated brine (> 75 g/L) can be attributed to the combined effect of reducing the transmembrane osmotic pressure difference via a draw solution, and operating at high hydraulic feed pressures. This approach has been incorporated into a standard ultrafiltration and reverse osmosis desalination plant to increase the process recovery. In total, five different OARO integrated flow processes are modelled numerically to determine their technical and economical feasibility in maximising the process recovery. Three of the five presented OARO integrated flow processes are novel, and offer technical and economical advantages over the previously proposed OARO processes. At lower feed salinities, OA-5, which is a new process, is the optimal OARO integrated flow process. Recoveries of up to 72% from a 35 g/L saline feed are possible when operating at the membrane burst pressure of 48.3 bar. Furthermore, the energy consumption of OA-5 is approximately 4.00 kWh/m(3), which is significantly lower than that in currently employed high recovery thermal processes, such as mechanical vapour compression. OA-3 is another original OARO integrated flow process and is the most attractive at a higher feed salinity of 70 g/L. The maximum recovery of 44% is achieved at an average energy consumption of 6.37 kWh/m(3). The results presented in this article demonstrate that pressure-based membrane processes can competitively concentrate brine streams to concentrations of up to 125 g/L.