Water Quality, Treatment and Purification

Quality of water is an important criterion in water supply. Water as it exists in nature contains many impurities. Water in clouds is very pure but it picks up various gases, dust and other impurities while falling in the form of rain through atmosphere.Some of the rain water seeps through the ground and reaches the ground water.On its way, the water picks up minerals and other impurities. The other part of the rain water which flows on the surface in the form of streams in to water bodies such as ponds, lakes and rivers. This water while flowing dissolves organic and inorganic impurities from rocks and land surface. As discussed earlier, water is tapped for supply form either ground water sources or surface water sources.

When water is drawn from these surface water sources or ground water sources, it needs some purification process to remove these impurities.Most industries will have to treat all or part of the water for specific usage. Feed water for boilers is of particular importance and requires many treatments. Water used as ingredient obviously requires treatment specific to the product. This normally includes removal of odours, colour, chlorine, and turbidity. Water used in cooling towers or can cooling systems requires treatment to inhibit corrosion of surfaces and deposits or stains on surfaces. Treatment will include removal of hardness and specific ions such as iron and manganese, removal of gases, and addition of substances such as chromate. Usually, surface water requires a greater degree of treatment compared with ground water due to the larger amount of impurities present. However,ground water sometimes requires special water treatment processes, e.g., removal of Fe, Mn, fluoride, etc. Physical, chemical and biological characteristics of water give the indication of impurities present and play a vital role in design of water purification processes. We will discuss some of these processes in this unit.