Tuesday, January 22, 2008

AIEEE Chemistry UNIT 18B Water and Soil Pollution


Water Pollution: Major pollutants such as, pathogens, organic wastes and chemical pollutants; their harmful effects and prevention.
Soil pollution: Major pollutants such as: Pesticides (insecticides,. herbicides and fungicides), their harmful effects and prevention.Strategies to control environmental pollution.

Hard water is any water containing an appreciable quantity of dissolved minerals. Soft water is treated water in which the only cation (positively charged ion) is sodium. The minerals in water give it a characteristic taste. Some natural mineral waters are highly sought for their flavor and the health benefits they may confer. Soft water, on the other hand, may taste salty and may not be suitable for drinking.

Water must be treated to remove undesirable substances before it can be distributed for domestic use. The type of treatments used is a function of the undesirable components that are present. Often it will be necessary to remove sediments, iron, mang anese, hardness (calcium and magnesium) and pathogenic bacteria. In the aeration process, air is pumped through the water to remove undesirable gases and volatile compounds. Iron and manganese are also precipitated in this stage. Addition of lime caused calcium and magnesium to precipitate out of solution. Coagulants are often used to remove colloids, algae and further clean the water. Carbon dioxide is then used to return the pH to near 7. Final treatment often involves addition of chlorine to disinfect the water by killing pathoghens.

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