Flash mixers and Flocculators are conventional mixers used for chemical coagulation and flocculation in water and wastewater treatment processes.
The flash mixer is a rapid mixing unit that is designed for a retention time ranging from 30 seconds to 3 min [Typical]. The design of the Flash mixer includes impellor blades located connected vertical shaft and rotates in an axial direction. This vertical shift is driven by a speed reducer [gear box] and an electrical motor.
Rapid mixing usually occurs in the regime of turbulent flow in which inertial flow predominates. Higher the velocity, and the greater the turbulence, the more efficient the mixing will be. The purpose of a Flash mixer is to destabilize or finely divide particles [impurities like solids or emulsified oil] using chemicals called coagulants.
Typical chemicals used for chemical coagulation in water and wastewater industries are Alum [Aluminum Sulfate], FeCl3, and PAC [Poly Aluminum Chloride]. The chemical quantities that are to be added for the water and wastewater treatment process have to be found out through a jar test.
Flocculator is a slow mixing unit that is designed for a retention time ranging from 10 minutes to 30 minutes [Typical]. The flocculator design consists of a series of appropriately spaced paddles mounted on either horizontal or vertical shafts. This vertical shift is driven by a speed reducer [gear box] and an electrical motor.
The slow-moving paddles in the flocculator promote increased particle contact which in turn increases particle agglomeration or formation of flocs. Flocculation is a transport step that brings about the collisions between the destabilized particles [as a result of chemical coagulation] needed to form larger particles that can be removed readily by settling units [DAF or lamella].
Typical chemicals used for chemical flocculation in water and wastewater industries are Poly electrolytes [anionic or cationic]. The chemical quantities that are to be added for the water and wastewater treatment process have to be found out through a jar test.