Modelling, simulation and optimisation of seawater reverse osmosis – pressure-retarded osmosis (SWRO–PRO) hybrid units for seawater desalination

Abstract Reverse osmosis (RO) is the most widely used membrane-based desalination technology. However, it still requires a significant amount of energy to produce fresh water. The highly concentrated rejected solution of the RO process is typically wasted. The idea is to use it for pressure-retarded osmosis (PRO). A SWRO–PRO hybrid system could potentially further reduce the specific energy consumption (SEC) of the system. In this paper, we are modelling the membrane unit for both RO and PRO in detail. The mathematical model describes the important flow quantities along the flow direction of the membrane. For a realistic approximation, we include internal concentration polarization (ICP) and external concentration polarization (ECP) effects. Together with a model for a modern energy recovery device (ERD), we are able to implement and simulate a complete SWRO–PRO hybrid system. Finally, we optimize the operating pressures of a conventional RO system and the operating conditions of a hybrid system.