Quantifying the potential of high-performance RO membranes for seawater and hypersaline brine desalination: from module-scale modelling to experimental evaluation

Abstract

High-pressure reverse osmosis (HPRO) is emerging as a promising technology for treating hypersaline brine from seawater RO (SWRO) processes. However, little guidance currently exists on the performance limits of HPRO membranes in terms of the water permeability and selectivity. In this study, we modelled fluid dynamics and mass transport within RO pressure vessels to explore performance gains from improved membrane properties. Our simulations indicate that tripling the baseline water permeability (from 0.45 to 1.35 Lm⁻²h⁻¹bar⁻¹) of HPRO membranes could reduce energy consumption by 23 % or cut the number of pressure vessels required by 62 %, for an HPRO plant operating at 50 % recovery. To complement the modelling work, we experimentally evaluated 12 state-of-the-art RO membranes under HPRO conditions simulating SWRO brine treatment (130 bar, 70 g/L NaCl, 10 ppm boron). In closed-loop tests, the membranes demonstrated water permeability values ranging from 0.34 to 0.87 Lm⁻²h⁻¹bar⁻¹, with 98.7–99.6 % salt rejection and 77–93 % boron rejection. In 50 % recovery tests reflecting real-world operation, achieving drinking water standards proved challenging, with permeate concentrations ranging from 708 to 1990 ppm NaCl and 1.6–4.1 ppm boron – exceeding regulatory limits for potable use. To address this, we conducted a second-pass brackish water RO at 75 % recovery, using the HPRO permeate as feed (2000 ppm NaCl, 4 ppm boron). The additional second-pass RO step successfully reduced permeate concentrations to 75 ppm NaCl and 0.35 ppm boron, meeting drinking water quality standards. This work is expected to provide guidance in terms of HPRO system design for hypersaline brine treatment.