Energy-positive brine management in the Aral Sea: a techno-economic water–energy nexus framework based on reverse electrodialysis

Hypersaline inland water bodies are a growing environmental and management challenge. Yet, they remain largely overlooked in the water–energy nexus. Here, we present a systems-level framework for energy-positive brine management using reverse electrodialysis (RED). Our approach explicitly addresses the complex multi-ion chemistry characteristic of inland hypersaline basins. A Pitzer-based thermodynamic model is coupled with a hydraulically constrained RED stack design and techno-economic analysis. This setup evaluates performance under realistic seasonal conditions. We apply this framework to the South Aral Sea basin as a representative case. The system achieves net electrical conversion efficiencies of 8.8–19.2% across seasonal temperatures. The seasonal average is 14.4%, governed by temperature-dependent ionic activity and conductivity. The effective NaCl-equivalent activity of the hypersaline brine is constrained to 1.00 1.11 mol kg⁻¹, much lower than ideal-solution estimates. With equal brine and treated wastewater flow rates at baseline operation, post-stack effluent mixing yields about a 50% reduction in bulk brine salinity per pass. The resulting levelized cost of electricity ranges from €0.16–0.31 kWh⁻¹ across seasons. The annualized average is €0.22 kWh⁻¹ when viewed as a joint cost of electricity generation and brine remediation. Sensitivity analyses show membrane spacing and lifetime are key economic drivers. Pump efficiency plays a secondary role. More broadly, the integrated thermodynamic–electrochemical–economic workflow is transferable to other hypersaline lakes and engineered brine systems. It provides a physically consistent basis for evaluating RED as a coupled energy-generation and brine-management technology under real multi-component water chemistries.