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Data is collected using process controller. It is stored in process controller and then analyzed.
Results
Results
The team had difficulty finding the correct alum dose at low temperatures and incoming turbidity this semester. The team determined a relationship between the WFP's PAC (polyaluminum chloride) dosage and the alum dose at the plant. The composition of PAC is a trade secret and its chemical formula is unknown. The relationship was determined between the percent active ingredients in PAC and alum. At the plant 48.8% of 11.1 lb/gal alum is active and 33% of 10.84 lb/gal of PAC is active. Therefore 1 ppm of PAC should have the same effects on flocculation as 0.182 mg/L alum.
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Figure 1: Effluent Turbidity vs. Alum Dosage. (12/14/08)
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Once this relationship was determined, it was used to set the flocculation tank dosage. The resulting dosage was much lower than expected. At average incoming turbidity of 2.3 NTU it was determined that the optimal alum dose would be around 4 mg/L (Figure 1). As can be seen in the figure below this alum dose gave the best effluent quality, although the differences in NTU between 4 mg/L and 9 mg/L are very slight.
The configuration of the uniform and tapered flocculator was changed to agree with the energy dissipation model of flocculation. Previously the end of the tapered flocculator the baffle spacing was 15 cm, this resulted in a energy dissipation lower than the recommended value of 0.4 mW/kg. In order to achieve the recommended value of energy dissipation the spacing in the flocculator was changed to 13.2 cm. This value was calculated using the equation:
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The spacing of the uniform flocculator was altered to match the last section of the tapered flocculator so that floc break up would not occur due to shear in the uniform flocculator. The resulting energy dissipation values for the tube flocculator are given a flow rate of 100 L/min:
Section | Spacing | Energy Dissipation mW/kg |
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1 | 3.339 | 98.65 |
2 | 3.952 | 50.268 |
3 | 5.794 | 10.88 |
4 | 10.071 | 1.192 |
5 | 13.232 | 0.4 |
A turbidity profile for the uniform and tapered flocculator was determined using this alum dose. The results are inconclusive- neither configuration produced an effluent with a lower turbidity than the raw water entering the flocculator. Furthermore in the graph shown below the flow rate was decreased to 13.6 gal/min producing an energy gradient of only 0.055 mW/kg throughout the uniform flocculator
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Figure 2: Uniform vs. Tapered Configuration. (12/14/08)
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