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We speculate failure of the data to fit because the experiment was conducted with such a low influent turbidity, there are less colloidal particles present in the water and less probability for these particles to collide with one another. Hence, for this experiment, the shortness of the flocculator and the limited effect of the alum caused the failure of producing a significant improvement in the turbidity of the water. There will need to be a higher collision potential for these particles to successfully collide and create bigger flocs necessary for a successful flocculation. The residual turbidity graph (Figure 1) shows the resulting mean turbidity settling down to around 2 NTU starting from the alum dose of 20 mg/L.

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Looking at the gamma PDF curve (Figure 2A) the alum dosage of 10 mg/L demonstrates an unusual behavior compared to the other doses; it has a very narrow distribution focused at a particular sedimentation velocity. It is suspected that the statistical functions we used to fit the data, did not fit the data right. Also, it could possibly be the case that this resulted from an unexpected presence of a large floc that might not have been representative of 10mg/L dosage but rather at the time the process controller recorded that reading a large floc happened to intersect. An option would be to either re-run the experiment or accept that we cannot fit it to the data. Otherwise 20 and 30 mg/L follow the trend well. From the residual turbidity graph (Figure 2B), there is also an unusual trend with the alum dose 40 mg/L; its turbidity unexpectedly peaks and results in an unusually high mean turbidity. (Can you speculate as to why this is the case?) In figure 2A, the alum doses 20 and 30 mg/L have wider distributions of floc sizes compared to those of other alum dosages. The wider distributions correspond to a wider variation in mean particle size. The average particle size for the 30 mg/L are only slightly higher than all the others. for 20 mg/L it looks similar to all the others. Overall, there seems to be discrepancies between the data recorded in the two graphs. From the values of mean turbidity at settling state, from 10 to 45 mg/L the mean turbidity seemed to start at a value of .608 NTU then rise to about .725 at 25mg/L, then rises to .829 and then back down to .755 at 35 mg/L.

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In the gamma PDF graph (Figure 3A), the alum dosage 10 mg/L shows a wider distribution with more probability to produce flocs. In addition, looking at the residual turbidity graph (Figure 3B), the resultant turbidity this dosage gives is significantly higher than the rest. The residual turbidity graph also shows the alum doses 15 mg/L and 20 mg/L to be producing a slightly higher resultant turbidity. From the values of mean turbidity at settling state, starting from the alum dosage 35 mg/L, the mean turbidity settles down to a constant value around 2.5 NTU.
(You are saying the say thing above. Lower alum dosages produce a larger range of floc sizes. Put these two figures into one or choose the ones that best represent this trend and comment on this)

3A
3B
FIGURE 3A: The graph plots normalized turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~50 mg/L; FIGURE 3B: The graph plots the residual turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~50 mg/L

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