Experiment 5: Alum dose = 105 mg/L
This is an a significant overdose. The graph below shows the effluent turbidity plotted against time for capture velocities of 0.058, 0.116, 0.174, and 0.231 mm/sec, for the low floc blanket level only.
Figure 1: Effluent Turbidity vs. Time for Floc Blanket on low, alum dose = 105 mg/L
Conclusions
This dosage showed poor floc blanket performance, which was the goal of this experiment. However, given that this is an extreme overdose, the resulting effluent turbidity is not as high as expectedexperiment was meant to demonstrate poor performance with an alum overdose. While the effluent turbidity averages less than 1 NTU, it is inconsistent and frequently spikes above 1 NTU for all capture velocities, meaning this is a demonstration of failure.
The failure of the overdose can be attributed to a less effective floc blanket. This occurs since the flocs that form with an overdose are larger and "fluffier" than they would be with normal dosing, forming a less dense floc blanket that is less effective in trapping and filtering out flocs. As a result, the system fails to consistently yield an effluent turbidity of less than 1 NTU.