In the initial step, the interparticulate forces responsible
for the stability of the particulate are reduced or eliminated by addition
of suitable chemicals. Subsequently, particulate collisions occur
due to transport by molecular motion or mechanical mixing. If these
collisions are successful, aggregation
occurs. Ordered collisions due to differential relative particulate velocities achieved by mixing and differential settling. Flocculation basins and mixing devices achieve this. Mixing devices increase the velocity of the water carrying the suspended particles and these results in more collision and more
aggregates and consequently more settling out of suspension.