Sewage treatment. Sewage is water containing waste matter produced by people. Much industrial sewage contains harmful chemicals and other waste materials. Sewage must be treated before it flows from sewerage systems into lakes, rivers, seas, and other bodies of water. Untreated sewage contaminates the water and, in time, can kill fish and aquatic plants. The sewage makes the water unsafe to drink and can also prevent use of the water for swimming, fishing, and other recreation.

Water treatment. Almost all untreated water contains bacteria, viruses, and other tiny organisms. Cities and towns obtain water from one of two sources: (1) the ground or (2) rivers and lakes. Water from rivers and lakes is piped from its source to a treatment plant, where chemical and physical processes purify it. Pipes under the streets distribute the water to houses and other buildings.

Water softening is a method of removing from water the minerals that make it hard. Hard water does not dissolve soap readily. It forms scale in pipes, boilers, and other equipment. The main methods of softening water are the lime soda and the ion exchange processes. In the lime soda process, soda ash and lime are added to the water in amounts determined by chemical tests while in the ion exchange process, the water filters through minerals called zeolites. As the water passes through the filter, the sodium ions in the zeolite are exchanged for the calcium and magnesium ions in the water, and the water are softened. Some cities and towns, however, prohibit or restrict the use of ion exchange equipment on drinking water, pending the results of studies on how people are affected by the added sodium in softened water.

The System of Water Treatment Plant (see pictures)

     click here to see the enlarged image