Page History

...

To find the ideal alum dosage for a certain influent turbidity, there are several qualities that must be considered. First, the resulting floc size should be large enough so that by the time it reaches the sedimentation tank, it will weigh enough to sink and settle out. Second, the resulting NTU must be small indicating an efficient flocculation/sedimentation process and clean water, and third, the alum dosage should preferably be low to save cost.

For the first experiment, the 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 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 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 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 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 dosage of 40, there was not a considerable change in the lowest NTU range. So the Alum doses lower than 45 mg/L were eliminated, and the Dose range was again narrowed down to 45~55 mg/L.

...