Modeling Pressure Retarded Osmosis Assisted Desalination System Performance

Pressure retarded osmosis (PRO) can be used in conjunction with reverse osmosis (RO) in a coupled system called PRO-assisted desalination (PRO-AD). The PRO-AD system can provide a solution to reduce the energy and environmental costs of RO desalination by reducing energy requirements and enabling discharge of brines at lower concentrations. The PRO sub-system utilizes semi-permeable membranes to treat impaired water while harvesting the chemical potential energy difference between RO brine and impaired water. A model was developed to design the PRO-AD system and predict potential performance of the system.

The objective of this research is to determine the lowest specific energy consumption of the system by optimizing both the RO and PRO sub-systems. Theoretically, the PRO-AD system could be energetically neutral because the energy spent by RO to desalinate seawater is the same as the energy produced to dilute brine back to seawater with PRO. However, due to thermodynamic restrictions and membrane imperfections for both processes, an energetically neutral PRO-AD system may not be currently possible. The focus of this presentation is to discuss the improvements in PRO membranes and module configurations that will increase the water flux and energy production of the sub-system in order to get as close to an energetically neutral PRO-AD system as possible.