Pressure retarded osmosis: advancement in the process applications for power generation and desalination

The current study highlights the advancement in Pressure Retarded Osmosis (PRO) process and covers most recent development in the process applications. The first application of PRO process goes back to 1973 by Sidney Loeb who suggested using the concept of osmotic energy for power generation. In principle, two solutions of different concentrations are separated by semipermeable membrane of, relatively, high water permeability and solute rejection rate. The high-concentration solution is usually known as the draw solution while the low-concentration solution is called the feed solution. The draw solution is pressurized before entering the membrane. Due to the osmotic pressure gradient across the membrane, fresh water transports in the direction of the osmotic pressure gradients resulting in the dilution of the high-concentration solution. After leaving the membrane, the diluted draw solution is depressurized in a turbine system for power generation. Different types of membrane materials and solute gradient resources were proposed and their impact on the performance of PRO process was investigated. In addition to power generation, the hybridization of PRO process with membrane and thermal processes for power generation and seawater desalination is not unusual nowadays. The current study provides a critical review about the recent advancements in the PRO process and research outcomes. © 2014 Elsevier B.V. All rights reserved.

In general, more laboratory and pilotplant experiments are required to optimize the operation parameters of the PRO process including pretreatment of feed solution, feed and draw solutions flow rates, feeds concentrations, cleaning protocol, and membrane type. There is a wealth of studies carried out to fabricate high performance membranes as mentioned earlier here. However, these studies are still in the laboratory scale and large pilot plant test is required to demonstrate the practicability of these membranes. Furthermore, long-term pilot plant test is required to evaluate the cost-effectiveness of PRO process including capital and operation cost, maintenance, and membrane replacement cost. More work is required to optimize the draw and feed solutions characteristics and impact on the process efficiency. Additional work is also required to produce and standardize the design of PRO membrane. Limitations of PRO process such as PRO membrane, membrane fouling, reverse salt diffusion and draw solution should be more investigated in the future work and preferably by pilot plant tests.