Tube Flocculator

Graduate Student: Ian Tse

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Objective and Motivations

The goal of any flocculation process is to transform suspended colloidal particles into flocs that can be removed by sedimentation. The design of sedimentation tanks is dictated by the settling velocity of the flocs. Floc capture requires that the fluid residence time in a sedimentation tank or in plate or tube settlers be greater than the time required for the flocs to settle out. Therefore, one design goal of flocculators is to create flocs with sufficiently high sedimentation velocities. Unfortunately, guidelines for proper design and operation of hydraulic flocculators are incomplete. The appropriate energy dissipation rate required at different points along the flocculator that will produce the best flocs is not well understood. It is expected that high energy dissipation rates will initially enhance the collision frequency of small particles creating larger floc aggregates, however high energy dissipation rates are also likely to cause break up of large flocs.

In orthokinetic flocculation, differential velocities cause flocs to collide. A percentage of these collisions result in adhesion and the further growth of flocs. It has been shown that the frequency of collisions is related to the magnitude of the energy dissipation rate present during orthokinetic flocculation. As flocs grow larger, they become more susceptible to breakup. Thus, a continuum of energy dissipation rates affects floc growth and breakup in orthokinetic flocculation. Eventually the particle size distribution can reach a pseudo-steady state during which breakup balances aggregation (Spicer & Pratsinis, 1996).

Our goal is to determine the parameters (such as optimal energy dissipation rate, hydraulic residence time, etc.) that will produce fast settling flocs that can remove the greatest percentage of the turbidity in the water.

Previous Research

Our previous research prior to Fall 2009 includes the development of FReTA and the accompanying data analysis tools that are capable of capturing the settling velocity distribution and post-sedimentation residual turbidity of a flocculent suspension. FReTA was also used to explore fluid shear and hydraulic residence time influences on hydraulic flocculator performance.

Spring Semester 2008 Research Goals

The team has discussed and agreed on several important goals to focus on for the Spring semester 2008:

1. Analyze the data from the Fall Semester 2007 and make solid conclusions. The team will look into further analytical tools such as Excel, MatLab, and MathCAD to handle and display the data in a better, more user friendly format. The team last semester found that the current MathCAD file is hard to use, for example if the user wants to isolate one run in a series of iterated experiments or compare certain runs to each other on the same graph.
2. Develop models to describe what is happening in the flocculator. The team will use this to determine what parameters are important in regulating the flocculation process.
3. Literature research to compare research, to see if previous similar experiments have been conducted, or for inspiration for further experiments or data analysis.
4. Find the relationship between G and Gθ. This is the ultimate goal that the team is trying to determine, it will take a combination of data analyses, modeling, and maybe more experimentation.

Ongoing Research - Spring 2008

• Developing analytical methods for understanding flocculation/settling data from our tube flocculator apparatus
• Augmenting sampling frequency and accuracy of our nephthelometric turbidimeters by accessing raw voltages directly from sensor
• Reevaluating the efficacy of tube flocculator setup & designing methods to eliminate sedimentation within flocculator and maintaining quiescent conditions in the settling volume
• Determining settling velocity and floc concentration using PIV.
• Writing tutorials on [Process Controller].

Future Research - Beyond Spring 2008

• Using PIV to evaluate floc formation from previous experiments: varying alum dose and varying G in flocculator
• Once the new IR turbidimeter is up and running, re-run previous experiments from last semester and compare settling curves
• Develop Process Controller Tutorial and exercises for future team members

Tube Floc Presentations

February 20, 2008
Our understandings on the tube floc research is summarized in the teach-in [presentation|Tube Floc^Tube_Flocculation_SP08_Teach-In.ppt].

March 25, 2008
Ken Brown's visit [presentation|Tube Floc^Tube Floc - Ken Brown Presentation.ppt]

May 10, 2008
Final presentation

FAQs, Basics, and Cleaning

If you are new to the team or would like to know more about the upkeep of our experimental setup, check out the basics.