Pressure retarded osmosis (PRO) as an option for Energy Recovery and cost reduction during seawater reverse osmosis (SWRO) desalination process by utilizing treated wastewater: A technical and feasibility evaluation

This study investigates the potential energy savings and economic feasibility of a hybrid Pressure Retarded Osmosis (PRO)-Seawater Reverse Osmosis (SWRO) system for desalination, focusing on a bench-scale test utilizing a cellulose tri-acetate (CTA) membrane with a 60 m² area. Key findings show that the PRO-SWRO hybrid system can achieve energy savings exceeding 28%, compared to conventional SWRO systems, by recovering energy from SWRO brine. At an optimal PRO feed pressure of 30 bar, the hybrid configuration reduces electricity consumption significantly, with a power density of 2 W/m² and flux of 2.4 L/min from feed to draw solution. Techno-economic analysis reveals that the viability of this system heavily depends on electricity costs. The breakeven PRO membrane costs were calculated for varying electricity prices, demonstrating that higher electricity costs make the system more economically attractive. For example, with electricity at 0.08 $/kWh, the payback period reduces to 2 years when using membranes priced at $450. Conversely, lower electricity costs require more cost-efficient membranes to maintain profitability. The study further explores the potential of using renewable energy sources to power the system, particularly in remote areas where electricity costs are high, such as the Farasan Islands. The findings suggest that the PRO-SWRO hybrid can enhance energy efficiency, making desalination more sustainable, especially when membrane costs align with breakeven values derived from this research. The results also highlight the potential of using PRO systems to offset energy consumption in wastewater treatment plants, enhancing the overall energy balance of water management processes.