Scale-up and simulation of multistage osmotically assisted reverse osmosis systems for zero liquid discharge applications: potential and limitations of real industrial modules

Zero Liquid Discharge (ZLD) strategies are increasingly adopted across industrial sectors to minimize freshwater withdrawal and eliminate wastewater discharge. Conventional ZLD schemes combine membrane pre-concentration with energy-intensive thermal steps such as evaporation and crystallization. In this context, alternative membrane-based technologies like Osmotically Assisted Reverse Osmosis (OARO) have emerged as promising candidates to push brine concentration beyond the limits of standard RO, potentially reducing the load on thermal systems. However, most literature studies rely on idealized models or lab-scale modules, lacking validation under real operating constraints. This work presents a rigorous comparative analysis of OARO configurations using real 4040 spiral wound modules experimentally characterized at pilot scale. The study evaluates the performance, energy efficiency, and system complexity of several multistage OARO schemes, by a process simulation approach that incorporates module-specific hydraulic limitations and pressure drops. Results show that while OARO configurations can achieve concentration targets similar to High-Pressure RO (TDS ~100,000 ppm), they do so at significantly higher energy costs (13.4–19.5 kWh/m 3 vs. 7.8 kWh/m 3 for HPRO) and with increased membrane area and complexity. A further scenario was simulated where OARO is applied downstream of HPRO, showing that although additional water recovery (up to 150,000 ppm TDS) is achievable, the required membrane area and energy consumption (~32 kWh/m 3 ) make this approach unfeasible with current technology. The analysis demonstrates that only by including real-module constraints can OARO performance be realistically assessed. While OARO holds potential, HPRO currently remains the more robust and cost-effective solution for ZLD implementation in industrial brine management. • A validated OARO model was integrated into Aspen Plus® for process simulation. • OARO layouts compared for SEC, membrane area, and operational complexity. • Sweep solution recompression back to RO accounts for up to 50 % of energy use. • OARO shows higher SEC and complexity than HPRO for the same targets. • Hybrid HPRO–OARO reached 150,000 ppm but needed 160 modules and 32 kWh/m 3 .