Pilot Scale Demonstration of Low-Salt-Rejection Reverse Osmosis (LSRRO) Desalination of High Salinity Brines

Low-salt-rejection reverse osmosis (LSRRO) is a novel RO process configuration capable of treating hypersaline brines that conventional seawater reverse osmosis (SWRO) cannot. LSRRO can operate under hydraulic pressures similar to those of SWRO, thereby having lower specific energy consumption than thermal desalination. This study presents a unique demonstration of LSRRO. Five feed streams, from simple NaCl solutions (70 g/L total dissolved solids (TDS)) to oil and gas produced water (133 g/L TDS) were used to assess the performance of a pilot LSRRO system, using water recovery and stream compositions as performance metrics. The results confirm the capability of LSRRO to achieve water recoveries greater than 60% while generating brines with TDS concentrations higher than 200 g/L, far exceeding conventional SWRO performance, while limiting hydraulic pressure to 1,100 psi (75.8 bar). Water flux through the nine unique LSRRO membranes was also evaluated, and the results will help fine-tune salt and water permeabilities for future membrane fabrication. Overall, the rejection of select ions was more than 99% across all experiments, producing high-quality permeate with TDS concentrations ranging from a low of 31 mg/L to a high of 333 mg/L. Membrane integrity testing revealed a lack of damage or scaling after the experiments.