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The data processor was unable to fit the sedimentation velocity vs. turbidity curve into a gamma pdf graph,because the trend of our mean turbidities was not following a gamma distribution(Figure _A). We suspect that it could not fit because of a low influent turbidity of 5 NTU, and how our lowest mean effluent turbidity was less than ideal at 1.978 NTU.

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FIGURE 1: The graph plots turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~50 mg/L;

On November 11, 2009, an experiment was conducted with the turbidity set around 25 NTU, flocculator length 2796 cm, flow rate of 5 mL/s, and alum dosage ranged from 10 to 50 mg/L.

In the gamma PDF graph (Figure 2A), the alum dosage 10 mg/L showed a larger distribution of floc sizes with more probability to produce smaller flocs. In addition, looking at the residual turbidity graph (Figure 2B), the resultant turbidity this dosage gave was significantly higher than the rest. The residual turbidity graph also showed the alum doses 15 mg/L and 20 mg/L to be producing a slightly higher resultant turbidity. From the values of mean turbidity at settling state, starting from the alum dosage 35 mg/L, the mean turbidity seemed to be settling down to a constant value around 2.5 NTU.

2A 1B 2B
FIGURE 2A: The graph plots normalized turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~50 mg/L; FIGURE 2B: The graph plots the residual turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~50 mg/L

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