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Figure 1 shows both the raw water turbidity and the effluent turbidity as a function of the flow rate. The effluent turbidity increases with the flow rate. This shows that filter performance decreases with increasing flow rates, meaning that in order to achieve a desirable effluent turbidity, a lower flow rate and thus a larger filter tank size must be employed. As show in the graph, filtration velocities of less than about 2 mm/s produce an effluent turbidity of less than one, or a pC* of greater than 0.9. The graph in figure 1 appears to be a linear function. This can be explained by the idea that at lower flow rates, the foam is able to capture even the smallest particles, since they have been made sticky from contact with alum. However, as the flow rate increases, it become increasingly difficult to capture smaller particles as they are more difficult for the foam to hold on to. When the flow rate increases, it likely pushes these smaller particles right through the filter, resulting in increased turbidity. Figure 1 shows that as the flow rate increases, the minimum trapped particle size likely increases as well. 
Figure 1: Raw Water and Effluent Turbidity vs Flow Rate 
Figure 2: pC* vs Flow RateWhile the results obtained using this alum dose were phenomenal, this is a very high, unrealistic alum dose. To actually achieve this alum dose level, it would be necessary to install an additional alum doser prior to the filtration unit.
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