In Oman, up to 94% of available fresh water is used for agriculture.  A variety of techniques are currently being used to purify saline water. The most common are thermal methods such as multi-stage flash, and membrane techniques, as in the case of reverse osmosis. The cost of water production by these techniques varies from US$3.0-6.0/m³ depending upon the size of the plant and technique employed . 

Due to limited water resource and high cost involved in such desalination processes, large-scale production of water for agricultural commodities is not a viable option.   Enhancement of humidification dehumidification in greenhouse using saline water may provide a low-cost solution to one of the world's greatest needs: water for agriculture. The proposed study deals with the investigation of humidification/dehumidification processes in a greenhouse of the Agricultural Experiment Station of Sultan Qaboos University.  The design of evaporator and condenser will be investigated and optimized to enhance fresh water production under Omani weather conditions. In addition, a Fuzzy Logic based control system will be developed to optimize efficiency of the water production and water use in the greenhouse using digital controllers.

The concept of humidification of air, followed by dehumidification to collect fresh water is not new but the idea of combining this process with cultivation of crops is certainly innovative.  This combination is a very promising alternative, especially for Oman, since it produces fresh water from seawater or brackish groundwater.  The evaporating process in the greenhouse cools and humidifies the growing environment and creates optimum conditions for the cultivation of temperate crops.  The ambient air is blown over evaporators and humidified by seawater falling over them. The cool and humidified air creates a growing environment that substantially reduces the amount of water required by plants. At the back of the greenhouse, fresh water is produced by condensing the humidified air using cold deep-seawater or cold water coming from the front evaporator (Figure 2). The amount of fresh water produced depends upon the local weather conditions, greenhouse parameters and cold water temperature required for condensing the air.

Up to now, this concept has only been tested with a prototype on the Canary Island of Tenerife (Paton and Davis, 1996). The results from this pilot study are very encouraging.  Further research, however, is necessary to validate the concept and demonstrate its potential for Oman and other arid regions. (Click here for more info)

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Paton, A. C. and Davis, P. (1996). The seawater greenhouse for arid lands. Proc., Mediterranean Conference on Renewable Energy Sources for Water Production