An accurate approach to the design of channel hydraulic flocculators

The design of flocculators for water treatment continues to be based on the generalized and simplistic concept of mean velocity gradient within the reaction zone. This approach makes little sense for hydraulic flocculators in which the turbulence conditions are heterogenous. A theoretical, experimental and computational fluid dynamics study is presented, in which a point-to-point approach is derived, allowing variations in turbulent kinetic energy to be taken into account in determining flocculation efficiency. Results for the point-to-point calculation are compared with experimental measurements of flocculation efficiency in a full-scale model of a channel hydraulic flocculator, and an extremely good fit is obtained, demonstrating the point-to-point approach to be an accurate method of determining flocculation efficiency in channel hydraulic flocculators. A design example is presented showing how the point-to-point approach can be used in practice. It is concluded that the point-to-point approach is a much better method of design than that based on the mean velocity gradient.