High-Desalination-Performance Solar Still With a Sustainable Carbonaceous Biopolymer as a Photothermal Interface

Background: Conventional solar stills (CSS) suffer from low thermal efficiency and limited freshwater output. To overcome this limitation, this study investigates a sustainable and cost-effective performance optimization technique using local carbonaceous waste. Specifically, variable-thickness layers of plant tar are utilized as a biostructured, photothermal material to enhance heat retention at the water surface and boost desalination performance in arid regions like El Oued, Algeria. Methods: An experimental comparative analysis was conducted between a CSS and modified solar stills equipped with plant tar layers of varying thicknesses. The evaluation monitored daily freshwater productivity and thermal efficiency under identical local meteorological conditions. Furthermore, a comprehensive economic viability assessment was performed to calculate fabrication costs and payback periods. Results: The modified stills demonstrated significantly superior performance, delivering freshwater productivities of 1.35 L/day, 1.44 L/day, 1.49 L/day, and 1.56 L/day (at a 1.00 cm thickness), outperforming the CSS (1.00 L/day) by 35%, 43.8%, 49%, and 56%, respectively. Thermal efficiency followed a matching trend, peaking at the 1.00 cm coating thickness due to optimal heat localization. Economically, although the modified stills have slightly higher fabrication costs compared to the CSS 12,550 DA(USD 96.90). 11,300 DA(USD 87.21), they prove highly profitable, recouping the initial investment in just 2.74 months (82 days) compared to nearly 4 months for the CSS. Conclusions: This study demonstrates that local carbonaceous waste can be efficiently valorized as a high-performance photothermal material for solar distillation. The proposed system offers a highly profitable, sustainable, and accessible solution for supplying drinking water to populations in arid zones, directly contributing to the achievement of Sustainable Development Goal 6 (SDG 6).