Energy recovery in brackish water reverse osmosis: Modeling, integration, and cost-saving analysis

Brackish water reverse osmosis (BWRO) desalination is an essential option for inland potable supply. This study evaluates the integration of an isobaric energy-recovery device (ERD) model PX-L140, into a BWRO line using a coupled field–model approach. A low-pressure pressure exchanger (PX) was retrofitted on a 2,400 m³·d⁻¹ train and operated under steady conditions; the plant-wide SEC fell by 10.8% (0.82→0.73 kWh·m⁻³; average power 82.0→73.1 kW) while maintaining ~80% recovery and product quality. The high-pressure duty decreased by ~15.7%, consistent with isobaric transfer efficiency at moderate pressures. A validated techno-economic model was used to map feasibility versus feed salinity and capacity: at an energy tariff of 0.13 USD·kWh⁻¹, simple payback is ~11 years at 2,400 m³·d⁻¹ and 4 g·L⁻¹ TDS, improving to below 3 years near 5,000–5,600 m³·d⁻¹ or at higher tariffs. These results provide actionable guidance for utilities on when ERD retrofits are technically and financially justified in BWRO.