Techno-economic assessment of a demand-responsive RO-PRO superstructure for sustainable saline wastewater treatment

As global water scarcity and rising energy demands intensify, hybrid Reverse Osmosis Pressure Retarded Osmosis (RO-PRO) systems offer a promising solution for efficient water and power recovery. However, under fluctuating demand, membrane allocation can lead to higher specific energy consumption (SEC), reduced operational efficiency, raising concerns for long-term sustainability. To address these challenges, this study proposes a superstructure-based RO-PRO (S-RO-PRO) framework designed to maximize freshwater production and energy generation. The proposed methodology combines system-level, multi-stage RO and PRO unit configurations with demand-side management (DSM) strategies designed for building communities. The results showed that across different demand scenarios, the S-RO-PRO outperforms the conventional RO-PRO, achieving a 10–25 % reduction in SEC. Moreover, it sustains stable power densities of 2–5 W/m² compared to 0–1 W/m² in the conventional system, achieves energy cost reductions of 40.30–51.11 %, and maintains up to 55 % higher net present value under high-demand conditions, underscoring its strong cost-saving potential. Overall, the DSM-adapted S-RO-PRO can make a significant contribution to the development of efficient water-energy systems while supporting circular economy principles and long-term sustainability.