Test Suspension for FReTA

Introduction

The AguaClara Team has been using the tube floc apparatus and FReTA to collect empirical data on flocculation. This experimental apparatus has been created based on existing knowledge on flocculation and fluid mechanics; with resulting values looking plausible, the team has assumed the system to be working as intended. However, questions on the scientific basis of the collected results have arisen: how valid is the data from this particular experimental set-up and on what verification is the team assuming the workability of the apparatus?

In order to answer these questions, the Tube Floc Team has chosen to design a small experimental apparatus focusing on the validation of FReTA. Creating a small loop that will pump water directly to FReTA at certain influent turbidity, this apparatus will measure the sedimentation rate of the flocs quickly and efficiently. The purpose of this set-up is to empirically observe and compare the settling velocities in varying turbidity and to see how these experimental data match theoretical values. To make this comparison, influent turbidity needs to be controlled with colloidal particles of known densities and physical qualities, such as mass. The properties of the actual colloidal particles in water are hard to determine since they vary both in size and densities. So instead, the team will be using particle beads of microscopic size at two differing masses. Mixing these particle beads with clean, distilled water of minimal NTU, the settling velocities of the beads will be measured.

The density of the particle beads are going to be known values given when purchased. The settling velocity will be found using the following equation with input values of gravity (g), density of bead (ρbead), density of water (ρH2O), and the kinematic viscosity of water (ν).

Comparing the theoretical settling velocity to that of the empirical, the workability of FReTA will be shown.

With two masses chosen to be tested, the Tube Floc Team is expecting to see a drop in turbidity in two different phases: one when the heavier particles and lighter particles are present in FReTA together, and another, after the heavier particles drop first, and only the lighter ones are present in the system. With the measured turbidity vs time, the data will be processed through Process Controller to convert the information to a graphical overview of sedimentation velocities.