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 teamCurrently, the AguaClara team has built a new, more robust baffle system for the small scale vertical flow hydraulic flocculator that models flocculation tanks built in plants in Honduras. This new baffle system allows for faster and easier adjustments to baffle spacing and arrangement. With the ability to adjust the spacing quickly, turbidity profiles of the tank can be compared for different baffle arrangements to determine which configurations work best for different raw water turbidities and will help verify the equations used by the Design team for energy dissipation. Uniform baffle spacing and tapered spacing will be tested. In tapered flocculation the flocs are exposed to high velocity gradients in the beginning of the tank and lower gradients as they travel through the tank. The key to having reliable and pertinent results is to keep the main variable, raw water turbidity, as standard as possible, meaning that multiple tests need to be run on the same day, when turbidity is over a small range. Having an easily and quickly adjustable baffle system will allow us to run multiple configurations in a short time period, making our results directly comparable to one another.

Methods and Research

Process Controller
Process Controller is used to control plant processes such as alum dosing, turbidimeters, etc and to collect data.

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