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Overall, this system performed well and most of the effluent turbidities were below 1 NTU. The ideal alum dose of 45 mg/L and the slight underdose and overdose of 35 mg/L and 65 mg/L, respectively, performed best. Because the "overdose" and "underdose" did not fail, as expected, it was necessary to test more extreme doses. We tested 15 mg/L and 105 mg/L to observe more severe conditions. The extreme overdose of 105 mg/L demonstrated failure, as expected. The 15 mg/L extreme underdose, however, did not experience failure.

Originially, an alum dose of 45 mg/L was thought to be an ideal dose. However, this alum dose did not perform as well as was expected. In comparison to the other average effluent turbidities, 45 mg/L should either perform slightly better than an alum dose of 35 mg/L or somewhere between 35 mg/L and 65 mg/L. As shown in the above graphs, 45 mg/L performs worse than all of the other alum doses, including what was supposed to be extreme under and over doses (15 mg/L and 105 mg/L). This should not have happened, and experiments at this alum dose may need to be re-run.

The major cause of failure for an underdose is an incomplete floc blanket as a result of smaller flocs that are formed, but the increased residence time in the flocculator creates larger flocs, which form a floc blanket more quickly and more effectively. Thus, although we expected that the extreme underdose of 15 mg/L would fail, the effluent turbidity fell within the acceptable range.

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