Sedimentation | Environmental Engineering | CE
Real Life Application
A concept used in the treatment of raw water before supplying the water to a city or a town. This is adopted for surface water where water has high concentration of finer suspended impurities and is one of the most important treatment given to raw water in a water supply treatment plant.
Removal of suspended impurities is essential so as to carry out the further treatment effectively. Sedimentation tank is used for this purpose where water is detained for a minimum duration (known as detention time) and the turbulence of water is removed. Due to the removal of turbulence of water the solid particles settles in the tank due to self-weight and are removed from water.
Specific Gravity is the basic principle for sedimentation process. Settling velocity of particles is an important parameter in designing of this treatment unit. It governs the rate of removal of solids and ultimately decides the efficiency of the sedimentation tank. The settling velocity corresponding to the minimum size of solids to be removed is known as design settling velocity or Surface Overflow Rate.
The settling velocity is dependent on the size of the solids and is directly proportional to the square of the diameter of particle.
Sedimentation tanks are of two types i.e. Quiescent type and Continuous type. In quiescent type, no flow of water takes place and in continuous type constant flow of water is maintained. Sedimentation tank is designed on the basis of various design aspects where dimensions of tank are determined by using surface overflow rate, detention time and design discharge.