Chemical and physical aspects of coagulation

Abstract

It is the aim of this contribution to identify situations where predominantly physical variables affect or even control the coagulation process in a chemically controlled and optimized system. Observations in technical systems show that the mixing of coagulation chemicals can be slower or faster, depending upon the hydraulic characteristics of the mixing reactor. This leads to satisfactory destabilization in one case and unsatisfactory destabilization in another, in particular if metal ions or hydroxilized metal species are used. It has been shown that the energy dissipation in stirred real reactors leads to a nonhomogeneous distribution in terms of the absolute size of the (locally linear) velocity gradient, i.e., aggregation conditions. This will be superimposed by the characteristics of the coagulating chemicals, i.e., the ability to form stronger or less strong flocs. Data on the separation effectivity of geometrically different units for systematically varied boundary conditions of the coagulation process show that one type of floc is withheld more efficiently than another in the same separation unit and likewise that one kind of separation unit may be more efficient for a specific floc.