Effect of membrane properties on the performance of batch reverse osmosis (RO): The potential to minimize energy consumption

Efforts to improve the performance of RO desalination include new membranes and new system configurations. Batch RO is an innovative configuration which helps to minimize Specific Energy Consumption (SEC) at high recovery. However, there is a lack of experimental studies regarding the performance of different membranes in batch RO. In this study, we tested four 8-in. RO membranes of different permeabilities in a free-piston batch RO system to assess how membrane properties affect performance. Tests were conducted with brackish feed water containing 1000–5000 mg/L of NaCl, at recovery of 0.8. Performance in terms of SEC, permeate quality and salt rejection was quantified. SEC and salt rejection varied considerably from low-permeability to high-permeability membranes. For the lowest permeability membrane rejection was >95 %, whereas for the higher permeability membranes it was only 82–96 %. SEC with high-permeability membranes was approximately 25–29 % lower than with the lowest permeability membrane. Using a verified model, we predict that on increasing the permeability from 5 to 20 L/m2/h/bar, hydraulic SEC would go down further by 17–28 % using ultra high-permeability membranes. Though this study shows the potential for SEC reduction, it also underlines the limitations of current commercial membranes and therefore the need for membranes with even higher permeability.