Water Desalination Literature Review

4. CHAPTER-2
4.0 LITERATURE REVIEW
4.1 Resources and Need for Water Desalination

The earth contains about 1.4×10⁹ km³ of water, which covers approximately 70% of the planet surface area; the percentage of salt water in this large amount is 97.5%. The remaining 2.5% is fresh water with 80% of this amount frozen in the icecaps or combined as soil moisture. Both forms are not easily accessible for human use. The remaining quantity, about 0.5%, is believed to be adequate to support all life on Earth. Unfortunately, this water is not distributed evenly throughout the plant and it is not available in sufficient quantities either when or where it is needed. Table 1 gives a summary for distribution of various water resources across the globe. The

Deep aquifers proved to be viable source for bottled drinking water. This is because of regulated and limited rates of water use from these sources insure sufficient natural replenishment of the source. Also, the natural process through various rock formations provides the water with natural minerals and keeps its pH at acceptable levels. Classification of various types of water is based on the purpose for which the water is used. The first water grade is set for safe drinking, household purposes, and a number of industrial applications. This water category has a salinity range of 5 to 1000 ppm. This type of water is found in rivers and lakes and can be generated by industrial desalination processes. In large cities, various levels of water salinity are used, where water with salinity below 150 ppm is used for drinking while higher salinity water of up 1000 ppm is used for various household applications. This proved to be more effective, because the average per capita consumption of the low salinity drinking water (150 ppm) is limited to 2 liters/day. On the other hand, the per capita consumption rate for other household purposes is 200-400 liters/day, which is used for cooking, washing, cleaning, gardening, and other purposes. On industrial scale, the most stringent water quality is set by the makeup water for boilers and applications related to the electronic

Desertification is primarily caused by unregulated humane activities that result in the destruction of delicate habitats, such as woodlands, rainforests, swamps, and Savannah. Many of the flat lands used for farming purposes are being turned into dessert because of the continuous loss of the rich top soil and poor farming practices. Similarly, over-grazing activities has quickly turned many of the Savannah land into desserts. Examples for desertification of Savannah are found in Sudan, Kenya, Ethiopia, and China. Another bad practice is the unregulated harvesting of woodlands for the production of wood lumber and paper pulp. Also, rainforests in equatorial regions, which are considered an essential element of the global environment, is being replaced at a steady rate by farming and mining land. Such activities are driven by greed and search for quick profit. Unfortunately, such delicate habitats never recover and eventually become new dessert