The effect of very high hydraulic pressure on the permeability and salt rejection of reverse osmosis membranes

We employ a stirred-cell reverse osmosis setup to demonstrate that a seawater reverse osmosis membrane can maintain excellent salt rejection at pressures as high as 172 bar. However, we also demonstrate a very significant drop in membrane permeability at high pressures – likely due to membrane compaction. At 172 bar, permeability is more than 50% lower than at a pressure of 34.5 bar. In addition, our results illustrate how flux fluctuates significantly in time when the pressure is removed and then reapplied, even for very short periods, in high pressure reverse osmosis processes – an effect that requires careful consideration from the perspective of process control and operation. From the perspective of membrane performance, RO is feasible at high pressures but distinct challenges are presented by reduced permeability and increased variability in flux.