Current research regarding the effects of lamella spacing on sedimentation is an extension of experiments completed during summer 2008: Summer 2008

Fall 2008 Research

Objectives

The purpose of this experiment is to determine the optimal plate settler spacing using tube settlers and a tube flocculator.

Methods

The experimental apparatus is designed to be as robust as possible allowing for various experiments to be conducted using the same setup. The setup is made up of three unit processes, the constant turbidity control, flocculation, and settling column. Our focus for the experiment is on the settling column, where we will be varying certain parameters. We optimized the turbidity control system and the flocculator to create ideal conditions for floc blanket formation and sedimentation in the settling column.

Schematic

Design Parameters (parameters/equations/length and diameter values/critical settling velocity values)

Uniform Flow

Uniform flow in the settling column is key for having laminar flow in the tube settlers as well as the creation of the floc blanket. As seen in the image to the right, a uniform flow is needed at the inlet of the settling tube so the flow becomes laminar before reaching the end of the tube. All design assumptions and parameters for the column are based on a laminar flow through the settling tubes.

Flow in to the system from the bottom of the settling column creates a jet in the center of the column, which is far from uniform flow. A typical dissipation ratio is 1:10; therefore, it would take on the order of 10 m for jet to dissipate in a column with a diameter 10 cm, as in the current setup. A cone with a ratio of 4:6 is used a diffuse to maximize the lateral spread of the jet. In addition to the cone, there is a mesh directly on top of the cone made of a 1 cm thick plastic sheet with uniformly distributed holes of 0.5 cm diameter. This mesh will break up the single jet coming from the column inlet, into several smaller, weaker jets that will dissipate quicker. The preliminary stages of the experiment will test the effectiveness of the cone and mesh system in dissipating the jet and allowing for optimal floc blanket formation.

Results and Discussion

Obstacles

Flow into bottom bucket
Flow through

Graphs and results from trials

Future Work

Varying
Flow rate
Floc blanket depth
Location of tube settlers