Underground condensation of humid air for drinking water production and subsurface irrigation

Condensation Irrigation (CI) is a combined system for solar desalination and irrigation and/or drinking water production. Solar stills are used for humidifying ambient air flowing over the saline water surface in the still. This warm, humid air is then led into an underground pipe system where it is cooled and vapour precipitates as freshwater on the pipe walls. If drainage pipes are used the condensed water and some of humid air percolate through the pipe perforations and irrigates and aerates the ground. Drinking water can be collected at the pipe endings when using non-perforated pipes. The CI system has attracted attention from several North African countries, and pilot plants are now in operation in Tunisia and Algeria. Mass and heat transfer in the soil around the buried pipes has been modelled to evaluate the theoretical potential for these types of systems and to gain understanding of the mechanisms governing their productivity. For a presumed reference system, the mean water production rate in the drinking water system was 1.8 kg per meter of pipe and day. When using drainage pipes for subsurface irrigation, this number increased to 3.1 kg/m/d, corresponding to 2.3 mm/d of supplied irrigation water.