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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 (what is this shear rate?), 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 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. 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 shown in Figure 1:

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

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