Plate Settler Spacing

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Introduction

This research is focused on a deeper understanding of the sedimentation process so that plants can remove flocs from clean water as efficiently as possible, allowing for successful chlorination of the effluent water. Currently, AguaClara plants use lamella in their clarification systems, which are a network of sloped, stacked plates that create narrow channels through which clarified water can flow.

To emulate lamellar sedimentation, we use tube settlers of various diameters, which simulate the effects of the lamellar plates.

A majority of flocs that enter these inclined channels settle out due to the force of gravity, significantly reducing effluent turbidity (Comment here about what turbidity is and why we are reducing it.) to increase the effectiveness of chlorination. There is no control of influent water parameters going to the plant, so there is a keen interest in developing a settling system that is robust -after floc blanket clarification that will produce less than 1 NTU water. (Comment on why 1 NTU is the goal and not 5 NTU by WHO standards or 0.2-0.3 NTU by EPA standards)

Ultimately, we hope to optimize the lamella design in order to achieve effluent water with a turbidity of 1 NTU or less -- even under water chemistry fluctuations and alum dose variation. At present the plate spacing, capture velocity, and velocity gradient formation are three of our key design limiting constraints.

Velocity Gradient Research

Past research has brought to light the importance of velocity gradients within the tube settlers. Flocs at the bottom wall of the tube that experience an upward velocity pull greater than the force of gravity pulling them down will roll up the wall and exit with the effluent water. Flocs are fractal particles whose effective diameters are sensitive to shear stress, organic material in the water, and influent turbidity, so determining their response to the velocity gradient may require more than just a simple force balance. Furthermore, the maximum velocity gradient achieved at steady state will fluctuate with a plant's influent conditions and choices for flow rate through their lamella.

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Research Plan