Laminar Tube Flocculator
Introduction
In the flocculation process, suspended particles collide with each other to coagulate and transform into larger flocs, with the help of a coagulant, that can be removed by sedimentation. 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. 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. 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. |
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 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. Detailed information on the ProCoDA Software as well as descriptions of the data analysis process can be found in the appendix of this M.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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Objective & Motivation
Flocculation is an important process to water treatment.
Semester 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 G¿. 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.
Past Research
The Lab Flocculator research team has an important focus on investigating the relationship between fluid shear (G) and its effect on overall flocculator mixing (G¿). Floc formation and breakup rates depend greatly on the G¿ parameter, which is intrinsically related to the fluid shear present inside a reactor. The semester research goals of the Lab Flocculator research team was to measure the relationship between G and G¿ by performing experiments using a coiled-tube flocculator experimental apparatus. The team decided to first perform experiments to determine the appropriate alum dose to achieve optimal floc formation for the experimental apparatus. Experimental data showed that a 25 mg/L concentration of alum produced the best results for a range of influent turbidity between 50-150 NTU and a humic acid concentration of 35 mg/L with minimal marginal improvements thereafter; thus, subsequent experiments were conducted with a constant 25 mg/L alum dose. Throughout the semester, the team was faced with numerous obstacles originating from the physical apparatus and the various software used by the team. Sedimentation of clay inside feed tubing and the flocculator inhibited various experimental controls including influent turbidity, flow rates, and also data collection. Measures were taken to overcome this issue, but sedimentation should ideally only occur in the settling column during the appropriate operational state. The flocculator team has overcome a large learning curve of needing to understand the experimental setup, Process Controller, and the MathCAD data processor tools. Much data was collected of different combinations of important variables such as flow rate, influent turbidity, and flocculator length. Currently, only a qualitative analysis of the data has been performed and the team is satisfied with the data set obtained. During coming semester, the team will focus on developing an analytical model to better analyze the data as well as to present it in intelligible figures and charts in preparation for publication.