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Previous research indicated that an alum dosage of 45 mg/L is considered to be ideal. This preliminary data is the base for further research. The graphs below show the effluent turbidity plotted against time for capture velocities of 0.058, 0.116, 0.174, and 0.231 mm/sec. Image Modified
Figure 1: Effluent Turbidity vs. Time for Floc Blanket on low, alum dose = 45 mg/L

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Figure 2: Effluent Turbidity vs. Time for Floc Blanket on high, alum dose = 45 mg/L

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It is expected that the effluent turbidity will increase with a higher capture velocity.  This is because a larger range of particle velocities that will make their way into the effluent (when the capture velocity is .058 mm/s only particles with a velocity less than this will get into the effluent, however when the capture velocity is .231 mm/s particles moving faster than .058 will now make their way into the effluent). This is evident in both graphs, as the general pattern of the data for all four capture velocities demonstrates this trend. In the high floc blanket state, for 0.231 mm/sec, the highest capture velocity that was tested, the effluent turbidity is significantly higher than the other three capture velocities.  This could be because floc particles rolled up the tube and into the effluent, even though their velocity was less than the capture velocity.  The curves do not follow the pattern of those in the low floc blanket state, where the overall trends for each capture velocity only differ by a small amount over the course of the six hour experiment. This unexpected data requires more investigation and testing to ensure that it is accurate.  .  A re-run of this experiment would confirm if floc roll-up is occuring at this capture velocity