Using CFD in the Study of Mixing in Coagulation and Flocculation

Abstract

Mixing has always been acknowledged to be one of the key issues in producing a good quality treated water in the chemical water treatment process. In the rapid mixing stage, where the inorganic coagulant is first mixed into the raw water, the charge neutralization step occurs in less than a second. This being the case, charge neutralization and adsorption are very mixing-sensitive processes. A lack of effective mixing when using inorganic coagulants results in chemical overdosing and decreased efficiency as sweep coagulation becomes the dominant mechanism for floe formation. On the other hand, in the flocculation stage excess velocity gradients should be avoided in designing a flocculator. This work highlights the possible use of computational fluid dynamics, CFD, in numerical modeling of mixing in water treatment processes.