Enhanced distillate production of stepped solar still via integration with multi-stage membrane distillation

Arid and coastal regions, such as Egypt, face significant challenges in meeting potable water demands driven by population growth and sustainable development. Energy-efficient desalination technologies are urgently needed to reduce reliance on conventional energy sources. This study introduces a novel integration of a thermal membrane with a stepped solar still, leveraging basin heat to drive membrane distillation (MD). The system employs multiple membrane layers and water-vapor absorbent wicks to capture vapor and transfer latent heat, enabling cascading preheating of brine layers. A validated mathematical model assessed the system's performance under varying conditions, accommodating up to ten stages. Results reveal that increasing MD stages significantly enhances productivity, achieving a peak daily output of 47 L/m² day-five times that of a passive multi-basin solar still. However, productivity gains plateau beyond three stages, indicating an optimal balance between complexity and efficiency. The system's performance is affected by ambient and seasonal conditions, including wind speed and temperature fluctuations observed during trials in June, May, and December, requiring additional modifications for stabilization. This study demonstrates the potential of integrating MD with solar stills as a scalable, energy-efficient desalination solution for arid regions. Future research should focus on optimizing stage configurations and evaluating economic feasibility for large-scale applications.