Solving the water scarcity problem by enhancing water extraction from air technology.

Summary Capturing water vapor from atmospheric air is a possible solution to local water scarcity, but it is very energy demanding. Energy consumption estimates of water-from-air technologies involving adsorption processes, thermo-responsive hydrophilicity switching polymers, air cooling processes, and reverse osmosis of deliquescent salt solutions reveal that these technologies are not competitive when compared with seawater desalination, and the use of fresh water and wastewater sources. They only become a viable option in the absence of local liquid water sources and when long-distance transport for socio-economic reasons is not an option. Of interest, direct solar-driven technology for water-from-air production is an attractive means to disentangle the local water-energy nexus. It is expected that climate change will accelerate the introduction of water-from-air technologies in local water supply schemes. The optimal water-from-air technology depends on the climate, relative humidity, and temperature profiles. A world map is presented, indicating the optimal geographic location for each technology.

No abstract

Desiccants are used in the process industry for the drying of technical gases. An emerging application is fresh water production from water vapor of atmospheric air using adsorbents in a day-night cycle. Water adsorption is performed at night and desorption using solar heat during daytime. In this paper a non-isothermal kinetic model of a packed bed of desiccant pellets is developed to determine possible uptake improvements by elucidating the complex mass and heat transfer interdependent resistances. Shallow beds thinner than 1 cm are required to handle bed diffusion and thermal conduction effects. Options for improvements regarding intragranular water vapor diffusion are limited. The adsorption process quickly becomes convection and radiation limited by the strong exothermicity of water adsorption.