Recent developments in solar-driven adsorption and humidification-dehumidification based hybrid desalination system: A state-of-the-art review

Abstract

Freshwater scarcity is a growing global challenge, emphasizing the need for advanced and sustainable desalination technologies. Adsorption desalination (ADS) and solar thermal humidification-dehumidification (HDH) systems are emerging as efficient, eco-friendly solutions. ADS utilizes low-grade thermal energy, operates with zero brine discharge, and has a water recovery ratio exceeding 80 %. Recent advancements in ADS include metal-organic frameworks such as composite adsorbents, which exhibit adsorption uptakes and significantly enhance performance compared to adsorbents. Raw silica gel (SG) and sodium polyacrylate (SP) are adsorbents, and SG/CaCl₂ and SP/CaCl₂ are composite adsorbent materials. Research indicates that composite adsorbents, such as SG/CaCl₂ and SP/CaCl₂, achieve the maximum specific cooling power, measured at 498.7 W/kg and 310 W/kg, respectively, compared to traditional raw or composite adsorbents in solar adsorption desalination systems. Employing raw silica gel within an ejector-integrated hybrid desalination system featuring heat recovery results in notable performance, including a gained output ratio of 2.76 and a specific daily water production (SDWP) of 83.1 m³/ton/day during June. Heat and mass recovery methods, such as pressure equalization and dual-stage evaporator-condenser configurations, have improved SDWP to ∼16 m³/ton/day and coefficient of performance (COP) to ∼0.87, reducing energy requirement. Results also reveal that with SP adsorbents, the hybrid system with heat recovery powered by solar energy (SE) and waste heat (WH) provides the cheapest desalinated water production costs (1.1 $/m³ for SE and 0.4 $/m³ for WH) among all systems. Solar thermal HDH systems are particularly effective for small-to-medium scale applications. Packing materials such as polypropylene and porous plastic balls in humidifiers and fin-tube heat exchangers in dehumidifiers enhances performance. Solar water heaters outperform air heaters due to water’s higher specific heat capacity, with optimized operating conditions achieving maximum efficiency. The freshwater production cost for a hybrid system (ADS+HDH based) using solar energy ranges between 1.4 and 2.24 ($/m³). This study integrates numerical insights from ADS and HDH systems, highlighting advancements in SDWP, COP, and cost efficiency. Future research should optimize adsorbent designs, reduce heat and mass transfer resistances, and develop low-regeneration temperature materials for sustainable and cost-effective freshwater production.