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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 removal via sedimentation requires the formation of flocs that have settling velocities greater than the average upflow velocity of the sedimentation tank. (Careful with your wording here. We don't want to create flocs that just settle out, we want to create flocs that will become fluidized and form a floc blanket) Therefore, an important design goal for AguaClara flocculators is to create flocs with mean sedimentation velocities larger than the design upflow velocity in the sedimentation tanks (Again, careful. If we did this, then we would never form a floc blanket).
Unfortunately, Guidelines for proper design and operation of hydraulic flocculators are incomplete. The appropriate level of mixing (quantified by the energy dissipation rate) required to produce flocs with a narrow distribution of high sedimentation velocities in a hydraulic flocculator is yet unknown. 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 break up 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) (Where can I find this reference on the wiki?).
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.
Research Goals
The research goals for each semester are provided below:
Future Challenges
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.
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. An excellent resource for information on the FReTA setup is Ian Tse's M.S. thesis: Fluid shear influences on hydraulic flocculation systems characterized using a newly developed method for quantitative analysis of flocculation performance. This thesis contains detailed information on the Process Controller states, rules, and set points as well as descriptions of the data analysis process.