The solar humidification–dehumidification method (HDH) is a thermal water desalination method. It is based on evaporation of sea water or

brackish water Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

and subsequent condensation of the generated humid air, mostly at ambient pressure. This process mimics the natural

water cycle The water cycle, also known as the hydrologic cycle or the hydrological cycle, is a biogeochemical cycle that describes the continuous movement of water on, above and below the surface of the Earth. The mass of water on Earth remains fairly cons ...

, but over a much shorter time frame.

Overview

The simplest configuration is implemented in the

solar still A solar still distills water with substances dissolved in it by using the heat of the Sun to evaporate water so that it may be cooled and collected, thereby purifying it. They are used in areas where drinking water is unavailable, so that cle ...

, evaporating the sea water inside a glass covered box and condensing the water vapor on the lower side of the glass cover. More sophisticated designs separate the solar heat gain section from the evaporation-condensation chamber. An optimized design comprises separated evaporation and condensation sections. A significant part of the heat consumed for evaporation can be regained during condensation. An example for such an optimized thermal desalination cycle is the multiple-effect humidification (MEH) method of desalination. Solar humidification takes place in every greenhouse. Water evaporates from the surfaces of soil, water and plants because of thermal input. In this way the humidification process is naturally integrated within the architecture of the greenhouse. Several companies like

Seawater greenhouse A seawater greenhouse is a greenhouse structure that enables the growth of crops and the production of fresh water in arid regions which constitute about one third of the earth's land area. This in response to the global water scarcity and peak ...

utilize this inherent feature of a greenhouse in order to conduct desalination inside the atmosphere of the facility.

Design

The method can be optimized by using various effects in the categories of thermal energy collection and storage for continued nocturnal operation, choice of site location, various evaporation effects, as well as condensator design and provision of cooling energy to harvest distillate from the moist air. A Desalination Greenhouse using all of the effects in all categories, with an emphasis on the optimized combination of the effects including synergies, is the

IBTS Greenhouse The IBTS (“Integrated Biotectural System")-greenhouse is a biotectural, urban development project suited for hot arid deserts. It was part of the Egyptian strategy for the afforestation of desert lands from 2011 until spring of 2015, when geopol ...

. The Global water cycle also includes all sub-effects of HDH, like increased evaporation over the oceans surface and surface increase by wind, making the generation of freshwater on the planet so efficient.

Tests

There are successful small-scale agricultural experimentation done in arid regions such as Israel, West Africa, and Peru. The major difficulty lies in effectively concentrating the energy of sun on a small area to speed up evaporation.

References

External links

Encyclopedia of Desalination and Water Resources
* The MEH-Method (in German with English abstract)
Solar Desalination using the MEH method, Diss. Technical University of Munich

Desalination Systems using the MEH-Process
Water treatment Drinking water Water desalination {{watersupply-stub