Vertical Flow Hydraulic Flocculator
Overview
Alum and raw water flow through a short series of pipe elbows acting as a rapid mix. This disperses the alum throughout the raw water stream, ideally coating a significant amount of the suspended particles. This mixed solution then enters the vertical flocculator. The flocculator is comprised of a series of channels with alternating up and down baffles. The baffles force water to change direction through an amount of space that is calculated to provide target mixing.
This mixing is vital to the water treatment process because it is the engine that drives floc formation. When alum is added to water it decreases the net charge on suspended dirt particles in the flow. When particles collide in an un-coagulated stream (one not treated with alum), they tend to repel one another. Conversely, particles in a coagulated stream are more likely to actually stick together and form larger conglomerates. These larger clumps of particles are referred to as flocs.
At the beginning of flocculation the particles are small. The vertical flocculator has many more tight turns, and therefore creates much more mixing in the early sections of the tank as compared with the later sections. As the stream mixes more and larger flocs form, the number of baffles per unit length of the tank decreases to reduce the strain on the larger flocs. The exact values for mixing parameters at various stages of floc formation is currently a central focus for the AguaClara laboratory research team.
Research
Developing Turbity Profiles along the Flocculator
Testing of Uniform Baffle Configuration
Testing and Tank Modifications
Construction History
Design
Flocculator Maintenance
Constant communication with the Cornell Water Treatment Plant was needed to attempt to integrate our pilot plant into their facility. Some modifications would be necessary after transportation and set up in the tank at the plant. We fabricated a frame to hold the rapid mix in place on the side of the tank. The inlet pipe had to be redirected to fit into the rapid mix pipe. Directing the inlet pipe directly straight down into the top of the rapid mix pipe would give us the maximum flow from that pipe. The outlet pipe was reconstructed to prevent leakage. Water from the treatment plant is directed to us before treatment. After the water is treated in our system the effluent exits the tank and reenters the treatment plant at the same point through a nearby drain. Assembly and installation of the turbidimeters, sedimentation tubes, and alum feeder were completed in the same day.
Other Resources
Overview
Currently, the AguaClara team has built a new, more robust baffle system for the small scale vertical flow hydraulic flocculator that models flocculation tanks built in plants in Honduras. This new baffle system allows for faster and easier adjustments to baffle spacing and arrangement. With the ability to adjust the spacing quickly, turbidity profiles of the tank can be compared for different baffle arrangements to determine which configurations work best for different raw water turbidities and will help verify the equations used by the Design team for energy dissipation. Uniform baffle spacing and tapered spacing by channel, a design caveat currently used by the Design team, will be tested. In tapered flocculation the flocs are exposed to high velocity gradients in the beginning of the tank and lower gradients as they travel through the tank. The key to having reliable and pertinent results is to keep the main variable, raw water turbidity, as standard as possible, meaning that multiple tests need to be run on the same day, when turbidity is over a small range. Having an easily and quickly adjustable baffle system allows for multiple configurations to be run in a short time period, making results more relative and comparable to one another.
A second system of baffles was also constructed so one system can be adjusted while another system is in and running tests. The systems can then be swapped in and out to run tests on different baffle configurations. Turbidity profiles will be obtained for a range of energy dissipation rates. The design team uses an energy dissipation rate of 0.4 mW/kg so energy dissipation rates around this value were tested, ranging from as low as .006 mW/kg to as high as 12.06 mW/kg. Instead of dosing alum as in years past, PAC was used as coagulant. This is the coagulant used by Cornell's Water Filtration Plant and because of this the pilot plant can dose PAC in the same ratio as the real plant, allowing for dosing to come directly from plant operators who are looking at effluent turbidity results for the water all day, making the dosing for the pilot plant more accurate and appropriate than if alum were being used.
Flocculator Methods and Maintenance
Flocculator Maintenance Procedures
How to clean the tank, fill it, empty it, and place the tube settlers.
Process Controller
Process Controller is used to control plant processes such as alum dosing, turbidimeters, etc and to collect data.
How to Run an Experiment
The method used to collect data along the flocculator.
For more general methods and maintenance (entire pilot plant) see the main maintenance page.
Construction History
Flocculation Tank Construction History
Construction of Tapered Baffles
Construction of Adjustable Baffle System
Research Projects and Results
Turbidity Profiles (Spring 2009)
The calculations and turbidity profile results of testing various uniform and channel-tapered baffle configurations.
Tapered vs. Uniform Baffle Configuration
Determined whether or not tapered flocculation was more efficient than uniform flocculation.
Flocculator Research (Spring 2008)
A report on all of the research conducted at the pilot plant in Spring 2008, including tank adjustments, turbidity profiles, and methodology.
Alum Dosing (Spring 2008)
The optimal alum dose for the flocculator was investigated.
Turbidity Profiles (Spring 2008)
Turbidity profiles were developed for the flocculator under various conditions.
Grab Sample Turbidity Testing (Spring 2008)
Develop a method to test the accuracy of the turbidimeters.
Testing of Uniform Baffle Configuration
Determined the turbidity profile for the Uniform Baffle Configuration.Research Log - Spring 2008