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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 cm23 m, 56 m, and 8388 cm84 m).

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, 28 m, (Why is this length different than the lengths shown above?) 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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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 cm28 m. 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 -water-water at extended flocculator lengths of 5592 cm and 8388 cm56 m and 84 m, or double and triple the length of the current flocculator.

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TABLE 1: Shows the Lowest turbidity reached by specific alum dosage ranging 30 mg/L~55 mg/L during an influent turbidity of approximately 100 NTU.
(The table of data doesn't mean anything yet. First, graph data rather than creating tables of numbers. Second, the residual turbidity must have been observed at some time. That time corresponds to a settling velocity. So report the turbidity at a particular capture velocity! It appears that you didn't do actual data analysis, but that you somehow read numbers (perhaps from a graph) and then copied them down. That leads to subjective analysis. Use data analysis in MathCAD and create a graph and then show that in the wiki. This data is hardly any real justification for the alum dose of 45 mg/L. Why not use 40 mg/L?)

For the second experiment, the alum dose range was set to be from 40mg40 mg/L to 110mg110 mg/L varying with an increment of 5mg5 mg/L (always leave a space between a number and the unit) and the influent turbidity set around 500 NTU. Repeating the process implemented for the first experiment, this data was run through Mathcad for an overview. However, unlike the previous experiment, looking at the gamma PDF graph (Figure 2) from Mathcad, the mean particle sizes did not vary significantly. With increasing alum doses, the floc size should have also differed. Yet comparing the size distribution for the lowest alum dose (40 mg/L) and the highest (110 mg/L), there was no comparable difference. In addition, reviewing the datalog, the approximate lowest NTU range also seemed to be similar (Table 2). From this analysis, we decided that either the accuracy of the result presented by this experiment was arguable or the alum dose of 40 mg/L was enough for effective flocculation. Since the dose of 40 mg/L seemed to have a similar effect as the higher alum doses, we decided to repeat this experiment with an expanded alum dose range to test even lower doses. An expansion of the range of alum dosages, from 10 mg/L to 100mg/L, was made to find the least alum dosage that will give effective flocculation.

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TABLE 2: _Shows the Lowest turbidity reached by specific alum dosage ranging 30 mg/L~55 mg/L during an influent turbidity of approximately 500 NTU.

(I am again doubtful of the data shown in this table. It it is calculated data, then how did the numbers end up with a squiggle in front? And how did it turn into a range? Standard analysis would report a mean and a standard deviation. It appears that all of the alum dosages tried were too high. What was the capture velocity used for this analysis?)