1.5 Water Treatment Processes

Laboratory analysis shows raw water contains low level turbidity of fine colloidal particles which cannot be removed by plain sedimentation, but required the use of chemical for their removal. The addition of chemical commonly Alum agglomerates the turbidity causing particles called flocs resulting in their rapid settlement and removal in the Sedimentation Tank. The process of Chemical addition and rapid mixing is called Coagulation whereas the process of formation of flocs is called Flocculation.

The process of removal of the flocs formed is carried out by allowing chemical mixed water to stand in a tank called Clarifier. During the period of retention in the tank, the flocs settle down at the bottom of the tank whereas the clear water is removed from the top. The settled solid are then removed from the bottom of the tank in the form of sludge. The process is called Sedimentation.

The clarification process has considerably removed the turbidity of water, but still it is undrinkable due to the presence of turbidity of very fine particles. In order to get rid of this level of turbidity water is passed through a sand bed which removes the remaining turbidity causing particles through the straining action of the sand. The process of passing water through a sand bed is called Filtration. The resulting water is free from turbidity.

In order to make treated water free from biological impurities, chlorine is mixed in water that removes all the biological impurities from water rendering it fit for human consumption. The process of killing of biological matter in the water through chlorine is called Chlorination.