Sedimentation Tank Hydraulics

Unknown macro: {float}

Introduction

A floc blanket is a dense, fluidized bed of particles that forms in the sedimentation tank below the plate settlers. A floc blanket helps to reduce effluent turbidity by trapping small flocs and reduces clean water waste through less frequent draining of the sedimentation tank.

The current design of sedimentation tanks in Agua Clara plants consists of plate settlers placed above the inlet manifold that catch flocs formed in the flocculator while allowing water to flow past the settlers into exit launders. The flocs then settle out at the bottom of the sedimentation tank and are removed regularly by a sludge drain. Implementing a floc blanket and a floc hopper in the sedimentation tank provide an additional method of filtration and will reduce sludge build up, instead allowing flocs to be wasted at a constant rate from the floc hopper.

Current and Future Research

We wish to determine optimal bottom geometry of a sedimentation tank for floc blanket formation. Floc resuspension is necessary for floc blanket formation so that flocs are recirculated through the tank instead of settling on the tank bottom as sludge. For adequate floc resuspension to occur, flocs settling in the sedimentation tank must be directed towards the path of the jet via an incline. We are examining mechanisms for floc resuspension for various bottom geometries by studying the relationships between hydrostatic pressure of solids built up on the sedimentation tank incline and and hydrodynamic pressure of the jet. We are also looking at parameters such as floc blanket formation time, clarified effluent turbidity, and tube settler turbidity for various bottom geometries, which will help us to determine the optimal bottom geometry given a specific design objective.

Our team is also working on designing a floc weir for the sedimentation tank, which will waste flocs at a constant rate from the floc hopper and serve to keep the floc blanket at a constant height.