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Looking at the gamma PDF graph (Figure 1A), the alum dosage of 20 mg/L gave a widely distributed probability of reaching different floc sizes with a comparably low probability to reach its highest sedimentation velocity. In addition, the residual turbidity graph (Figure 1B)showed a high turbidity for this alum dose in its lower velocity range. Thus the alum dose 20 mg/L seems to be inefficient for this particular influent turbidity and flow rate. The mean turbidity resulting from alum dose 55 mg/L seems to be out of normal range; its NTU value is significantly lower than the values given from the previous, lower alum dosages. Hence, the result from this dosage is doubtful. Overall, after the alum dose of 35 mg/L (except for 55 mg/L), the mean turbidity seemed to be settling down to a constant value around 1.4 NTU.

1A Image Modified 1B !
FIGURE 1A: The graph plots normalized turbidity vs. sedimentation velocity for each Alum dose ranging 20 mg/L~55 mg/L; FIGURE 1B: The graph plots the residual turbidity vs. sedimentation velocity for each Alum dose ranging 20 mg/L~55 mg/L

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In both graphs (Figure 2A, Figure 2B), the alum dosage 10 mg/L gave a comparably different result from the rest; it produced a significantly higher settling turbidity and a large amount of smaller flocs. The overall mean turbidity for this dosage was almost twice the following dosages. After the alum dose 50 mg/L, the mean turbidity seemed to be settling down to a constant value around 2.5 NTU.

2A !500NTULength1_GammaPDF.png,width=300,height=300! Image Added 2B
FIGURE 2A: The graph plots normalized turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~90 mg/L; FIGURE 2B: The graph plots the residual turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~90 mg/L

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