Types of Settling
In a very dilute suspension, particles will settle independently of each other and will not
interact. Quite often, however, we will come across suspensions in which the solids do interact.
In water treatment one of the most important stages of treatment is actually designed to
promote this interaction. We looked at coagulation and flocculation in the previous section and
how they cause particle interaction. There are four types of settling behaviour representing
increasing degrees of interaction. Well formed flocs settle at 3 m h
-1
, although the addition
of coagulant aids may raise this to as much as 10 m h
-1
.