Centrifugal reverse osmosis (CRO)-a novel energy-efficient membrane process for desalination near local thermodynamic equilibrium

Seawater reverse osmosis (SWRO) can address the global water crisis that is being exacerbated by climate change, industrialization, pollution, and population growth. However, conventional single-stage RO (SSRO) incurs a high energy cost owing to pressurizing the feed to that required for the desired recovery. This cost could be reduced if SWRO were operated at a progressively increasing pressure dictated by thermodynamic equilibrium for the local transmembrane salt-concentration difference. This is approached by the semi-batch closed-circuit RO (CCRO) process that progressively increases the transmembrane pressure (TMP); however, it incurs cumulative energy losses until the pressure is reached for the desired recovery. The centrifugal reverse osmosis (CRO) process uses rotation of a module to create a centrifugal force that increases the TMP differentially with increasing radial distance from the axis-of-symmetry. Unlike CCRO, CRO is a continuous desalination process. A mathematical model and preliminary design are advanced for a CRO module. CRO can reduce the net specific energy consumption relative to SSRO by 31% for 50% recovery at 56 bar from a 35 g/L seawater feed. A TMP progressively increasing from 28 to 56 bar can be achieved with a CRO module having a radius of 0.72 m rotating at 1000 rpm.