Analysis of the effect of alum dose and flocculator length on flocculation

Procedure

In Experiment 2 we investigated the effect of alum dosage on flocculator performance. The procedure for Experiment 1 contains information on the general setup used in this experiment. We used the same setup as in Experiment 1, but instead of varying flow rate, we varied the alum dosage. The plant flow rate was held constant at 5 mL/s (what is this shear rate?), and we used influent turbidities of 100 NTU and 500 NTU and three different flocculator lengths (23 m, 56 m, and 84 m).

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The following Process Controller Files were used for the 100 NTU and 500 NTU tests.
100 NTU Test File
500 NTU Test File

Results and Discussion

To find the ideal alum dosage for a certain influent turbidity, there are several qualities that must be considered. First, the resulting floc size should be large enough so that by the time it reaches the sedimentation tank, it will weigh enough to sink and settle out. Second, the resulting NTU must be small indicating an efficient flocculation/sedimentation process and clean water, and third, the alum dosage should preferably be low to save cost. (This is something minor, but we should also consider how the particle size distribution will affect the formation of a floc blanket as well. Producing very large flocs may not facilitate floc blanket formation as they will settle out before the floc particles could ever become fluidized)

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