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For the first experiment, the Alum Dose alum dose ranged from 20 to 60 mg/L varying with an increment of 5 mg/L and the influent turbidity was around 100 NTU. The data given from this experiment was processed through Mathcad for a simplified overview of the result in graphic form.

The gamma PDF graph shows the probability of reaching a certain floc size for each run of experiment with varying Alum alum dosage. The y-axis represents the probability and the x-axis represents the floc size. Looking at the gamma PDF graph (Figure 1) for this experiment, the Alum alum dosage of 20 mg/L was immediately eliminated from consideration for an alum dosage because its probability to reach a large floc size was comparably smaller than the others. In addition, the Alum alum dosage of 25 mg/L was eliminated because of its wide variation of floc sizes and relatively low probability to reach its largest size. Now narrowed down to an Alum alum dosage range of 30~55mg/L, the datalog for the experiment was used to find the lowest turbidity range during the settling state. As shown in table 1, after the Alum alum dosage of 40, there was not a considerable change in the lowest NTU range. So the Alum alum doses lower than 45 mg/L were eliminated, and the Dose dose range was again narrowed down to 45~55 mg/L.

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