Laminar Tube Flocculator
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Objective and Motivations
Introduction
In the flocculation process, suspended particles collide with each other to coagulate and transform into larger flocs, with the help of a coagulant, 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 To improve the performance of flocculators, we need to research how the design and operational parameters affect the aggregation and settling velocity of the flocs. One These parameters include energy dissipation rate, hydraulic residence time, coagulant dose, influent turbidity, etc. One of the goals for the AguaClara team is to develop a sedimentation tank that will form a fluidized floc blanket, which will help clean water as it flows into the sedimentation tank from the flocculator. To develop this floc blanket the flocculator must produce flocs that fall within a particular range of settling velocities. Therefore, it is important to research the parameters that affect flocculation and the resulting floc size distribution.
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)
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.
Our apparatus (flocculation residual turbidity analyzer or FReTA) is capable of measuring both settling velocity and residual turbidity under different flocculator operating conditions. Complete description and sketches of current apparatus setup can be found here.
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The goals of the Laminar Tube Floc Team are to determine the parameters that will affect influent turbidity removal and to develop flocculation models as a guideline for flocculation design. |
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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 tube flocculator 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 Detailed information on the Process Controller states, rules, and set points as ProCoDA Software as well as descriptions of the data analysis process can be found in the appendix of this M.
References
S. thesis.
Ongoing Research
* Determine the optimal orifice size for floc break up systems with four, eight, and sixteen clamps by gradually decreasing the clamp size based on the relationships between energy dissipation rate, floc size, terminal velocity, and clamp size until the flocculator performance worsens.
- Determine optimal positioning for floc break up points by comparing the residual turbidity of an evenly distributed clamp system with clamp systems that gradually decrease the number of clamps toward one or both ends of the flocculator. As residual turbidity decreases the flocculator performance improves.
- Compare the performance of tapered tube flocculation with regular tube flocculation. Design a tapered system -- small tube at the beginning, medium tube in the middle, and large tube at the end (same length for each size of the tubing) using 10 mg/L PACl dose and 28 m tube flocculator length (N://files.Cornell.edu/EN/aguaclara/RESEARCH/Tube Floc/Spring 2013/Experiments/Single PACl 10 mgL.pcm/). As tube size (diameter) increases, energy dissipation rate decreases, allowing flocs to continue to grow. The larger that flocs can grow, the lower the residual turbidity will be.2. Determine optimal positioning for floc break up points by comparing the residual turbidity of an evenly distributed clamp system with clamp systems that gradually decrease the number of clamps toward one or both ends of the flocculator. As residual turbidity decreases the flocculator performance improves.
Current Research (Spring 2015)
* Design and implement a settled water turbidity (SWaT) measurement system that can more accurately measure low turbidities than the previous FReTA system. Using this new SWaT system, repeat experiments using only one clamp of variable size on the middle of the tubing arrangement. Compare the results of these experiments with the results of the same experiments run using the FReTA system from the Fall 2013 research.
* Depending on the results of the middle-clamp testing, either run more experiments with variable number of clamps to further test the effects of clamps, or design and implement a tapered flocculator system with energy dissipation rates starting from 1000 mW/kg.
Challenges for Future Semesters
- Special Skills Needed:
More Information
Troubleshooting of the apparatus, Process Controller and Data Processor.
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Pratsinis, S., & Spicer, P. (1996). Shear-induced flocculation: the evolution of floc structure and the shape of the size distribution at steady state. Water Research, 30(5), 1049. Retrieved from Environment Index database.