Toward Sustainable Solar Interfacial Desalination in the Gulf Region: Empirical Testing and Cost-Effectiveness Modeling of a Bacterial Cellulose–Silica Composite with Photothermal Iron Oxide

This study examines the feasibility of a small-scale, solar-driven desalination approach as a complementary solution to addressing global freshwater scarcity, with particular relevance to the Gulf region. While large-scale thermal and reverse osmosis plants remain the backbone of water supply, they impose high capital, energy, and environmental costs. To address these issues, a low-cost prototype was developed using silica-agar composite reinforced with bacterial cellulose and biochar, with an iron oxide surface layer to enhance solar absorption. Laboratory experiments demonstrated substantial water uptake and localized heating, but also revealed constraints in evaporation efficiency due to continuous cooling at the liquid-air interface. The process of condensation emerged as the critical bottleneck, as only a small fraction of the generated vapor was transformed back into liquid. An economic assessment using the levelized cost of water suggest economic viability of the prototype that can be manufactured at low cost with no additional energy input. Further scenario sensitivity analysis indicates larger hydrophilic condensing surfaces, improved drainage and seals, and longer service life could increase both the performance efficiency and cost effectiveness when scaled. Overall, the prototype presents a promising potential for sustainable desalination in hot, high-radiance regions.