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Overview of Methods

     In these experiments the alum dosage supplied to the flocculation system was varied in order to study how floc and floc blanket formation affect the effluent turbidity produced by the tube settler.  The experimental set-up is identical to the one used in Spring 2009, and from our results we hope to analyze velocity gradient thresholds and possibly investigate how changing influent water chemistry affects the setter's efficiency.

Results and Discussion

     Using the Spring 2009 team's process controller methods, we subjected an ideal geometry to non-ideal conditions. Though the Spring 2009 team had success with a 9.5 mm diameter tube, due to a change in influent water chemistry over the summer, (ineffective air bubble traps in the flocculator,) or the addition of a flow accumulator to the method, we experienced failure with this geometry. We achieved an acceptable effluent turbidity (less than 1 NTU) with a 15.1 mm diameter tube that had a length of 30.5 mm. With the ideal results, we then subjected this tube settler to varying alum dosage to investigate the dependency of the performance of the tube settler on this parameter. At each alum dosage, the tube settler was tested at a variety of capture velocities and at two different floc blanket levels.

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Figure 1: Capture Velocity vs. Average Effluent Turbidity shown for each alum dose at low floc blanket level.


Figure 2: Capture Velocity vs. Average Effluent Turbidity shown for each alum dosage at high floc blanket level.


|| Floc Blanket Height || Alum Dose (mg/L) || 5 m/day || 10 m/day || 15 m/day || 20 m/day ||


| Low

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| 35

...

| .3136

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| .1799

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| .2353

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| .3093 |

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