Solar distillation can be used to make saline or brackish water potable. The first recorded instance of this was by 16th century Arab alchemists.[52] A large-scale solar distillation project was first constructed in 1872 in the Chilean mining town of Las Salinas.[53] The plant, which had solar collection area of 4,700 m², could produce up to 22,700 L per day and operated for 40 years.[53] Individual still designs include single-slope, double-slope (or greenhouse type), vertical, conical, inverted absorber, multi-wick, and multiple effect.[52] These stills can operate in passive, active, or hybrid modes. Double-slope stills are the most economical for decentralized domestic purposes, while active multiple effect units are more suitable for large-scale applications.[52]
Solar water disinfection (SODIS) involves exposing water-filled plastic polyethylene terephthalate (PET) bottles to sunlight for several hours.[54] Exposure times vary depending on weather and climate from a minimum of six hours to two days during fully overcast conditions.[55] SODIS is recommended by the World Health Organization as a viable method for household water treatment and safe storage.[56] Over two million people in developing countries use SODIS for their daily drinking water.[55]
Solar energy may be used in a water stabilisation pond to treat waste water without chemicals or electricity. A further environmental advantage is that algae grow in such ponds and consume carbon dioxide in photosynthesis.[57][58]
Solar energy has also been used for detoxification of contaminated water like distillery effluent via photolysis.[1] The economics of this process is though doubtful.
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