Vertical Flow Hydraulic Flocculator
Overview
Alum and raw water flow through a short series of pipe elbows acting as a rapid mix. This disperses the alum throughout the raw water stream, ideally coating a significant amount of the suspended particles. This mixed solution then enters the vertical flocculator. The flocculator is comprised of a series of channels with alternating up and down baffles. The baffles force water to change direction through an amount of space that is calculated to provide target mixing.
This mixing is vital to the water treatment process because it is the engine that drives floc formation. When alum is added to water it decreases the net charge on suspended dirt particles in the flow. When particles collide in an un-coagulated stream (one not treated with alum), they tend to repel one another. Conversely, particles in a coagulated stream are more likely to actually stick together and form larger conglomerates. These larger clumps of particles are referred to as flocs.
At the beginning of flocculation the particles are small. The vertical flocculator has many more tight turns, and therefore creates much more mixing in the early sections of the tank as compared with the later sections. As the stream mixes more and larger flocs form, the number of baffles per unit length of the tank decreases to reduce the strain on the larger flocs. The exact values for mixing parameters at various stages of floc formation is currently a central focus for the AguaClara laboratory research team.