Techno-economic assessment of batch reverse osmosis desalination systems: Rating and design

This study presents what is, to the authors' knowledge, the first techno-economic and exergetic assessment of pressure-exchanger-based batch reverse osmosis (PX-BRO) for brackish-water desalination. Unlike previous studies that primarily emphasized energy performance, the present framework integrates transient pressure-trajectory optimization with energetic, exergetic, economic, exergo-economic, and surrogate-model analyses. A transient model is developed by coupling feed- and permeate-tank mass balances with membrane transport, concentration polarization, and time-varying osmotic-pressure effects. The applied pressure is treated as an optimizable control variable, represented by a second-order polynomial and determined using particle swarm optimization to minimize specific energy consumption (SEC) at prescribed recovery. The model is evaluated over initial feed salinities of 1–10 g/l and recoveries of 0.4–0.95. Representative optimized cases yield SEC values of 0.538, 0.718, and 0.984 kWh/m³ at (4 g/l, 0.6), (6 g/l, 0.7), and (8 g/l, 0.8), respectively, with corresponding levelized cost of water (LCOW) of 1.50, 1.44, and 1.64 US$/m³. Across the investigated envelope, SEC increases monotonically with salinity and recovery, while exergetic efficiency increases mainly with salinity. The LCOW exhibits a minimum at intermediate recovery owing to competing production and energy effects. Cycle-based exergo-economic analysis confirms similar trade-offs. Finally, artificial neural network and regression models are developed for rapid prediction of SEC, second-law efficiency, and water cost within the investigated operating range.