New Options for Water Desalination

摘要

The world's total water supply is enormous compared with the presently conceivable needs of man, yet there is a growing water concern. Approximately 98% of the 320 million cubic miles of water in the earth's crust is salty and useful neither for irrigation by present techniques nor for the majority of man's other needs. Rain (the hydrological cycle) provides many times the world's annual water needs, but fresh water supplies vary not only widely over the earth's surface but also from time to time in a given region. This accounts for what has come to be referred to as the "water problem."In the United States, the actual "consumptive use" is only approximately 15% of the potential supply. In addition, water prices are low, and based on statistical analyses, there should be no major problem in most areas for many years in the future years. Although the United States is relatively well supplied with water, it continues to turn to sources other than rainfall and runoff. Parts of the Southwest have too little water to support rapid industrial expansion and California has embarked on projects to bring water nearly 1000 miles to Los Angeles and the southern part of the state. Outside of the United States, expensive desalination plants have been in operation for years, including in the Virgin Islands, the Persian Gulf, the West Indies, Libya, the Union of South Africa, Israel, and many other places. An obvious way to increase water availability is to recover fresh water through desalination from seawater or from the large underground stores of brackish water which are available in many arid regions. The authors are currently investigating other feed sources for producing potable water. An alternative is to find ways to use saline waters for agriculture and other purposes which require fresh water. This paper introduces the reader to the desalination process. Traditional processes are reviewed and 10 new options for desalination developed by the authors are presented. These include: a solar evaporator, a crystallization unit, a greenhouse solar evaporator, a simple evaporation (still) unit, a humidification/dehumidification unit, a heat conduit evaporator, a freeze desalination process, a mangrove process, a humidification unit, and a reverse osmosis/crystallization hybrid process. Details on each of the 10 processes are included in the presentation to follow.