Towards a low-energy seawater reverse osmosis desalination plant: A review and theoretical analysis for future directions.

Seawater is receiving consideration as an infinite water source in the current era of water shortage. The application of seawater reverse osmosis (SWRO) to prepare seawater for human use is increasing exponentially owing to its high energy efficiency among desalination technologies. However, SWRO is still energy-intensive, and thus needs to be improved further to become more environmentally sound (i.e., producing less CO 2). To tackle such a challenge, this study was conducted to propose strategies to lower the specific energy consumption (SEC) of the SWRO process. From the results of extensive review and theoretical analysis, three directions were proposed for improving the energy efficiency of the SWRO process: i) minimize the irreversible work of the high-pressure pump, ii) decrease the osmotic pressure of the feed, and iii) recover osmotic energy from reverse osmosis (RO) concentrate. After the feasibility of each approach was identified by assessing the theoretical minimum energy and the maximum available margin, strategies for each direction were presented with a technical description, then critically evaluated by considering their practical application. Because this paper includes theoretical perspectives for energy savings in SWRO, it provides comprehensive ideas for lowering the SEC of SWRO desalination plants in the future. Image 1 • Three improvement axes for low-energy reverse osmosis were analyzed theoretically. • Maximum margin and obtainable energy reduction in each axis were calculated. • Minimizing irreversibility is effective, but operating issues are challenging. • Decreasing osmotic pressure can be effective only with additional low-saline water. • Recovering osmotic energy may be effective, but needs to be further developed. [ABSTRACT FROM AUTHOR]