Investigation of the reduced specific energy consumption of the RO-PRO hybrid system based on temperature-enhanced pressure retarded osmosis

Reverse osmosis (RO) has been widely used as a dominant desalination technology to produce fresh water from seawater (SW), but still consumes huge energy. To reduce the energy consumption of RO, pressure retarded osmosis (PRO) has been developed to extract osmotic energy from RO brine. In this study, the PRO process is optimized for efficient energy recovery from RO brine via one system/module-level mathematic model in RO-PRO hybrid system. The system-level model illustrates that the specific energy consumption (SEC) of the hybrid system can be significantly reduced when achieving a high permeate flow under high operating pressure in PRO. However, the specific PRO membrane configuration has to sacrifice a high permeate flow under high operating pressure. The module-level model finds that the increase of PRO operating temperature facilitates to achieve a high permeate flow under a high optimal operating pressure. Furthermore, results present that the SEC at a kiloton-scale SWRO desalination capacity can be reduced by 14.41% (0.6M NaCl as a draw solution) and 17.93% (1.2 M NaCl as a draw solution) when the PRO operating temperature increases from 25 degrees C to 50 degrees C, confirming the great potential of temperature-enhanced PRO to further reduce the SEC of seawater desalination.