Water desalination using a novel solar still equipped with rotating desalination contactors (RDCs)

Abstract

This study presents a solar desalination system equipped with rotating desalination contactors (RDCs) a series of aluminum discs on a rotating horizontal shaft designed to expand evaporation and condensation surface areas, and experimentally evaluates its performance relative to conventional and drum-based solar stills. Key operating parameters including temperature, solar radiation, water depth, contactor speed and spacing, condensation area, seasonal variations, and operational mode were experimentally evaluated. A comparative evaluation between the RDC and the drum‑induced still was conducted, with results showing a 24% enhanced productivity for the RDC compared to the drum‑induced system, and an overall increase of more than three-fold (310%) over the standard passive solar still. Furthermore, the results showed that productivity tends to increase with reduced water depth (3 cm versus 6 and 9 cm), reduced disc speed (0.25 rpm versus 0.5 and 0.75 rpm), as well as reduced discs spacing (3 cm versus 6 cm). An increase in condensation area of 75.6% resulted in an increase in productivity by about 70%. Solar radiation completely eliminated bacteria from the feedwater. Statistical regression analysis confirmed strong correlations between productivity and the number of discs, rotation speed, and basin water depth (R² > 0.8). The optimized RDC unit (U3) achieved daily energy and exergy efficiencies of 75% and 10.4%, respectively, compared to 25% and 3.5% for the conventional still, with exergy destruction concentrated in the basin water. A detailed economic analysis showed water production costs between $0.103/L and $0.082/L across the units, with estimated payback periods under 7 months. A life cycle assessment (LCA) confirmed that despite higher embodied impacts, the RDC's greater productivity yields a net environmentally favorable outcome per liter produced. This novel modification renders solar stills more amenable to developing communities compared to the sophisticated, fossil-fuel-dependent desalination systems.