Coagulation requires the addition of alum in water stream and mixing to achieve a thorough dispersion of alum in water. The process of dispersing of chemicals is known as rapid mixing or flash mixing and the unit is called Flash Mixer.
The detention time is such that a complete homogenization of chemicals and water takes place.
Flash Mixer is a circular concrete structure/ mixing chamber equipped with mechanical agitator/mixer with an impeller to create turbulence in the mixing chamber for mixing alum. The size and shape of the mixer and the energy input shall be capable to produce a required degree of agitation. Alum solution prepared at the Chemical House shall be fed through a pipe in to the Flash Mixer. The governing factor for the design of Flash Mixer is a velocity Gradient (G) which is a measure of degree of agitation in the unit.
The required dose of alum shall be determined through jar test performed in the testing laboratory provided at the Treatment Plant. However, based on the jar tests performed on the raw waters of similar nature, an alum dose up to 60 mg/l of 15 % solution is adopted. Similarly a lime dose of 20 mg /l of 10 % lime solution is adopted in the design to control pH during coagulation process. The dosing pumps installed at the Chemical House are capable to dose a range of concentrations of chemicals.
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