Concentrated solar supercritical water desalination and multi-effect distillation hybrid systems for efficient zero liquid discharge

Concerns over brine discharge and carbon emissions from desalination operations are increasing due to rising freshwater production from desalination plants worldwide. To address this challenge, this study proposes concentrated solar supercritical water desalination (SCWD) hybrid systems. The concentrated solar thermal system captures high exergy from solar radiation. SCWD utilizes unique properties of supercritical water for non-phase separation, recovering sensible heat to reduce energy consumption, and achieve high recovery ratio for further zero liquid discharge (ZLD). The hybrid series configuration supply SCWD's waste heat to drive thermal desalination at lower temperatures and manage their brine. We investigate two integration options: multi-effect distillation (MED) and MED-thermal vapor compression (MED-TVC). We assess the impact of various operating conditions and key design parameters on system energy and exergy consumption, and conduct annual simulations based on meteorological hourly-resolved data. The results show that the SCWD-MED system is more efficient in energy and exergy consumption compared to SCWD-MED-TVC and standalone systems, while also showing strong economic potential. Adjusting the MED operating parameters (MED recovery ratio of 30 % and feedwater salinity of 55–60 g/L) can reduce the specific energy consumption of SCWD-MED to 34.2 kWh/m³. This results in a water production energy cost of $2.2/m³, 70.3 % of SCWD-MED-TVC and 57.5 % of standalone MED. Moreover, compared to the MED system at same solar thermal scale, salt recovery and efficient water production increases the annual profit by 9.6 times. Additionally, improving the heat exchanger effectiveness offer potential to reduce specific energy consumption by ∼40 %. This study provides practical design strategies for the future low-cost, large-scale application of solar-driven ZLD technologies.