On November 12, 2009, an experiment was conducted with the turbidity set around 5 NTU, flocculator length of 2796 cm, flow rate of 5 mL/s, and alum dosage ranged from 10 to 50 mg/L.
The data processor failed to fit a curve on the gamma PDF graph using our turbidity data Thus, the turbidity data did not fit the statistical distribution function (a gamma pdf) that we are using.
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,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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FIGURE 1: The graph plots the residual turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~50 mg/L
On November 17, 2009, an experiment was conducted with the turbidity set around 5 NTU, flocculator length of 8800 cm, flow rate of 5 mL/s, and alum dosage ranged from 10 to 50 mg/L.
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. 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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FIGURE 2A: The graph plots normalized turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~50 mg/L; FIGURE 2B: The graph plots the residual turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~50 mg/L
On November 11, 2009, an experiment was conducted with the turbidity set around 25 NTU, flocculator length 2796 cm, flow rate of 5 mL/s, and alum dosage ranged from 10 to 50 mg/L.
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.
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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
On October 20, 2009, an experiment was run with the set up of influent turbidity around 100 NTU, flocculator length of 2796 cm, flow rate of 5 mL/s, and an alum dosage ranging from 20 to 55 mg/L. The data obtained from this experiment was processed through Mathcad for a simplified overview of the results in graphic form.
The gamma PDF graph (Figure 4A) illustrates that the alum dosage of 20 mg/L gives a widely distributed probability of reaching different floc sizes with a comparably low probability to reach its highest sedimentation velocity. In addition, the residual turbidity graph (Figure 4B) shows a high turbidity for this alum dose in its lower velocity range. Thus the alum dose 20 mg/L seems to be inefficient for this particular influent turbidity and flow rate. The mean turbidity resulting from alum dose 55 mg/L is out of normal range; its NTU value is significantly lower than the values given from the previous, lower alum dosages. Hence, the result from this dosage is doubtful. Overall, after the alum dose of 35 mg/L (except for 55 mg/L), the mean turbidity settles down to a constant value around 1.4 NTU.
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FIGURE 4A: The graph plots normalized turbidity vs. sedimentation velocity for each Alum dose ranging 20 mg/L~55 mg/L; FIGURE 4B: The graph plots the residual turbidity vs. sedimentation velocity for each Alum dose ranging 20 mg/L~55 mg/L
On November 18, 2009, an experiment was ran with the set up of influent turbidity around 100 NTU, flocculator length of 8800 cm, flow rate of 5 mL/s, and an alum dosage ranging from 20 to 55 mg/L.
Looking at the gamma PDF graph (Figure 5A), all of the alum dosages give a similar result with their likeliness to produce similarly sized flocs at a similar probability. The residual turbidity graph (Figure 5B) shows alum doses 30 mg/L and 35 mg/L giving comparably higher resultant turbidities. Unlike the expected trend, rather than improving the turbidity of the water, the graphs show the deterioration of efficiency with more alum; the resulting turbidity seems to slightly increase with a larger amount of alum. Overall, there seems to be not much change with the increasing of alum dosage.
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FIGURE 5A: The graph plots normalized turbidity vs. sedimentation velocity for each Alum dose ranging 20 mg/L~55 mg/L; FIGURE 5B: The graph plots the residual turbidity vs. sedimentation velocity for each Alum dose ranging 20 mg/L~55 mg/L
On Oct 27, 2009, another experiment was conducted with the turbidity set around 500 NTU, flocculator length 2796 cm, flow rate of 5 mL/s, and alum dosage ranging from 10 to 90 mg/L.
In both graphs (Figure 6A, Figure 6B), the alum dosage 10 mg/L gives a comparably different result from the rest; it produces a significantly higher settling turbidity and a large amount of smaller flocs. The overall mean turbidity for this dosage is almost twice the following dosages. After the alum dose 50 mg/L, the mean turbidity settles down to a constant value around 2.5 NTU.
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FIGURE 6A: The graph plots normalized turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~90 mg/L; FIGURE 6B: The graph plots the residual turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~90 mg/L
On Nov 19, 2009, another experiment was conducted with the turbidity set around 500 NTU, flocculator length 8388 cm, flow rate of 5 mL/s, and alum dosage ranging from 10 to 90 mg/L.
In Figure 7A, the alum dose 10 mg/L gives a noticeably worse result compared to those of the higher dosages. Its distribution seems to primarily focus on the production of smaller flocs than the other alum doses. In the residual turbidity graph (Figure 7B), again, the alum dose 10 mg/L produces a higher effluent turbidity.
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FIGURE 7A: The graph plots normalized turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~90 mg/L; FIGURE 7B: The graph plots the residual turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~90 mg/L