(click to enlarge)
Plate Settler Spacing
The Plate Settler Spacing runs experiments with variable spacing between the plate settlers in an AguaClara sedimentation tank to optimize the sedimentation tank dimensions. The team hopes to find the minimum distance between plate settlers to significantly lower the height of the sedimentation tank. With the height at a minimum, the plan saves more material and construction costs which supports AguaClara's emphasis on efficiency. The team is currently exploring a system of failure, termed "floc roll-up". This mechanism is hypothesized to be caused by high velocity gradients near the wall that overcome the floc particles' settling velocity , which results in flocs rolling up into the effluent instead of settling down to the bottom of the tank. With smaller spacing between plates, the velocity becomes greater near the wall and thus increases the likelihood of floc roll-up becoming a failure mechanism.
The team predicts floc roll-up by using a dimensionless parameter called the Pi-ratio. This compares the terminal velocity of the slowest settling floc to the velocity experiences at the floc's outer diameter. When th Pi-ratio is less than one, it means that floc roll-up is the dominant mechanism for carrying particles to the effluent, while when the ratio is less than one, the convention considerations of capture velocity dictate the particle size range that should be captured.
To explore these velocity gradients, the team is designing and running experiments at a constant capture velocity, which is the settling velocity of the smallest particle a plate settler should be able to capture, based upon geometric considerations.