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An alum dose of 35 mg/L is considered to be a slight underdose. The below graphs show the effluent turbidity vs. time for the same capture velocities used for Experiment 1.
Figure 1. Effluent Turbidity vs. Time, floc blanket on low, alum dose 35 mg/L.
Figure 2. Effluent Turbidity vs. Time, floc blanket on high, alum dose 35 mg/L.
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Based on the results of this experiment, and an alum dose of 35 mg/L is not a significant underdose (The system preformed better. This cannot can not be considered an overdose)under dose. The system performed above expectations (compared to what. Please cite), , the effluent turbidity should have been higher than the effluent turbidity at the alum dose of 45 mg/L so we tested the system with an alum dose of 15 mg/L to see how the tube settler performs with a more extreme significant underdose.
Because lower capture velocities are supposed to perform better than higher ones, it is unexpected that the effluent turbidity for the capture velocity equal to .174 mm/s to be higher than the effluent turbidity for capture velocity of .231 mm/s. This is not consistent with what should have happened, and this experiment should be re-run to see if the data produced would be what is expected.