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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, and we used influent turbidities of 100 NTU and 500 NTU and three different flocculator lengths (2296 cm, 5592 cm, and 8388 cm).

In order to investigate alum dosage at a given turbidity and length, we planned to run two experiments. The first experiment would vary the alum dosage over a large range in larger intervals while holding the plant flow rate (shear), influent turbidity, and residence time constant. Then we planned to run a second experiment varying the alum dose across the best performing interval from the first experiment with small increments in order to determine the optimal dose.

For a flocculator length of 2796 cm, we began by testing water with an influent turbidity of 100 NTU with a plant flow rate of 5 mL/s. The alum dosage was varied from 20-60 mg/L in increments of 5 mg/L for each run. The alum dose was varied in process controller using the increment function.:

FIGURE 1: Process Controller setpoints used to vary the alum dose.

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However, since the optimal alum dosage for 100 NTU water has been well characterized by previous experiments and our the interval our data identified (see Results and Discussion) generally agreed with the known value of 45 mg/L, we did not continue with the second test at 100 NTU to narrow the optimal dose range and instead tested 500 NTU water. For the 500 NTU water, we maintained the same flow rate of 5 mL/s and flocculator length of 2796 cm. However, this time we varied the alum dose from 40 mg/L to 120 mg/L in increments of 10 mg/L. We then analyzed the data using the same methods as before.

We plan to continue our investigation of alum dose by performing a second experiment with 500 NTU water to find optimal dose based upon the best interval from our previous experiment. We will then repeat the process of varying alum dose over large intervals, and then narrowing to an optimal dose for 5, 25, 50, 100, and 500 NTU waterwater at extended flocculator lengths of 5592 cm and 8388 cm, or double and triple the length of the current flocculator.

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