Experiment 2: Alum Dose = 35 mg/L
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.
Conclusions
Based on the results of this experiment, an alum dose of 35 mg/L can not be considered an under dose. The system performed above expectations, 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 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.