Turbulence and Flocculation

Designers of flocculators are required to select the residence time, the number of flocculation compartments, the stirrer characteristics and the energy requirements, such that these function in an optimum manner in the treatment of a particular water. This paper presents a rational performance equation incorporating these parameters and demonstrates its validity with measurements employing a continuously operating model flocculation apparatus. Performance is shown to be determined by both the energy dissipation rate and the type of stirring equipment, but excessive energies result in floc breakup and reduced performance. At any particular performance a minimum residence time is shown to exist corresponding to an optimum energy dissipation. Anemometric measurements demonstrate a linear relationship between the mean square fluctuating velocity and the root mean velocity gradient computed from energy measurements. Whereas different stirrers have similar turbulence spectra, they display quite different performance coefficients.