RO experiments involved a cross-flow filtration system (Figure ) including a CF042 filtration cell (Sterlitech, USA) and ESPA1 RO polyamide membrane (Hydranautics, USA) as described previously . The experiments were undertaken at constant pressure (~60 bar) and temperature (25°C ± 2°C) with a 90 L h -1 feed flow rate (cross-flow velocity 0.28 m s -1 ). Permeate flux was monitored by a flow meter (µ-FLOW, Bronkhorst, The Netherlands). Experiments were undertaken once with a closed-loop configuration where the permeate flux was returned to the feed, and once with an open-loop configuration where the permeate was collected, with the feed content changing with filtration time. In both cases, the membranes were first compacted for 24 h by filtering DDW at 60 bar and NaCl solutions of similar EC at 60 bar. Feed and permeate pH and EC were monitored frequently, and samples were collected every few hours for ICP-AES analysis. On completion of the experiments, the membranes were removed from the filtration cell, washed gently, and dried before analysis. The membrane surface (coated with Au) was imaged by scanning electron microscopy (SEM; Jeol JSM-IT200, Japan) and the surface was analyzed by SEM-energy-dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD; Panalytical B.V., Almelo, The Netherlands) using a diffractometer with Cu Kα1 radiation (PANalytical Empyrean, The Netherlands).