Plate Settler Spacing
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| h1. Plate Settler Spacing
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h4. Introduction
This research is focused on a deeper understanding of the sedimentation process so that plants can remove flocs from clean water as efficiently as possible, allowing for successful chlorination of the effluent water. Currently, AguaClara plants use lamella in their clarification systems, which are a network of sloped, stacked plates that create narrow channels through which clarified water can flow.
To emulate lamellar sedimentation, we use tube settlers of various diameters, which simulate the effects of the lamellar plates.
A majority of flocs that enter these inclined channels settle out due to the force of gravity, significantly reducing effluent turbidity to increase the effectiveness of chlorination. There is no control of influent water parameters going to the plant, so there is a keen interest in developing a settling system that is robust \-after floc blanket clarification that will produce less than 1 NTU water.
Ultimately, we hope to optimize the lamella design in order to achieve effluent water with a turbidity of 1 NTU or less \-\- even under water chemistry fluctuations and alum dose variation. At present the plate spacing, capture velocity, and velocity gradient formation are three of our key design limiting constraints.
h4. Velocity Gradient Research
Past research has brought to light the importance of velocity gradients within the tube settlers. Flocs at the bottom wall of the tube that experience an upward velocity pull greater than the force of gravity pulling them down will roll up the wall and exit with the effluent water. Flocs are fractal particles whose effective diameters are sensitive to shear stress, organic material in the water, and influent turbidity, so determining their response to the velocity gradient may require more than just a simple force balance. Furthermore, the maximum velocity gradient achieved at steady state will fluctuate with a plant's conditions and choices for flow rate through their lamella.
[Subteam Semester Goals and Future Challenges|Plate Settler Spacing Goals]
[Weekly Subteam Progress|Plate Settler Spacing Meeting Minutes].
[Research Plan|Plate Settler Spacing Research Plan]
h2. Experimental Methods and Results
h3. Summer 2009
h5. [Experiments Varying Alum Concentration|PSS Summer 2009 Experiments Varying Alum Concentration]
This section contains the experiments in which the alum dose was varied in order to test how well the selected geometry (d = 15.1mm) performed when subjected to non-ideal conditions
h5. [Experiments with the Velocity Gradient|PSS Experiments with the Velocity Gradient]
The team has conducted physical modeling of the system to investigate the phenomenon of floc roll-up.
h5. [Filter Foam|PSS Filter Foam]
Due to a discrepancy in head loss, flow through each of the plate settlers in plants in Honduras is not equal. A geotextile foam was placed on top of the plate settler to create head loss and equalize the flow.
h3. Spring 2009
h5. [Experiments with Flow Rates and Inner Tube Diameters|PSS Tube Settler Experiments]
This section contains two related experiments. The first experiment varies flow rates and the inner diameter of the tube settler. From these results, the ideal L/d ratio is identified and held constant for a certain flow rate and inner diameter by varying the tube length.
h5. [Floc Blanket Formation|PSS Floc Blanket Formation]
Experiments exploring the rate of formation and density of floc blankets.
h3. Fall 2008 Preliminary Testing
h5. [Fall 2008 | Plate Settler Spacing Research Fall 2008]
This section contains preliminary observations and data that preceded the experiments run during spring 2009, above.
h3. Summer 2008 Preliminary Testing
h5. [Experiment Using Straws for Tube Settlers|Plate Settler Spacing Research Summer 2008]
These early experiments explored the impact of the diameter of tube settlers on effluent turbidity. Tube settlers were modeled using drinking straws.
h2. Additional Information
[Annotated Bibliography of Relevant Literature|PSS Bibliograhpy]
[Processor Controller Information|PSS Process Controller and Data Analysis]
[PSS Quiz for New Members |PSS Quiz]
[Fall 2008 Photo Gallery|Photo Gallery]
[PSS Apparatus Design] |