Overview of Methods
Robustness of our plate settler design is defined as the ability of the plate settlers to produce 1 NTU water over a variety of non-ideal conditions. One set of non-ideal conditions was building a floc blanket with underdoses and overdoses of alum to measure performance through effluent turbidity from the tube settler. Other non-ideal conditions that should be investigated are organic matter in the influent, varying influent turbidities, and other changes, such as pH, in the chemistry of the water.
Plate settler spacing is an important factor in determining the height of the plant clarifiers. Theoretically, if we could find a way to maximize their performance at the lower-limit of spacing and height it would be possible to decrease height of the sedimentation tank and lower plant costs.
In these experiments the alum dosage supplied to the flocculation system was varied in order to study how properties of flocs and the floc blanket affect the effluent turbidity produced by the tube settler. The influent water in our system had a turbidity of 100 NTU. Varying alum doses were then added to this influent.
The experimental set-up is identical to the one used in Spring 2009, and from our results we hoped to analyze velocity gradient thresholds and possibly investigate how changing influent water chemistry affects the setter's efficiency.
The influent water in our system has a turbidity of 100 NTU. Varying alum doses were then added to this influent. The alum dosage significantly affects flocculation, and thus plays a direct role in the success of the system (in the future, cite someone here either Matt, Ian's, or Monroe's fractal floc paper). The properties of floc particles combined with upflow velocity in the floc blanket will have a direct impact on effluent performance in the tube settlers (cite Matt's thesis here).
Plate settler spacing is an important factor in determining the height of the plant clarifiers. Theoretically, if we could find a way to maximize their performance at the lower-limit of spacing and height it would be possible to decrease height of the sedimentation tank and lower plant costs. +(This paragraph is out of place. Please put it in the appropriate spot)+
Results and Discussion
Using the Spring 2009 team's process controller methods, we subjected an ideal geometry to non-ideal conditions. Specifically we altered the alum dose to see how different alum doses affected the effluent turbidity. Though the Spring 2009 team had success with a 9.5 mm diameter tube, due to what we think was ineffective air bubble traps in the flocculator, or the addition of a flow accumulator to the method, we experienced failure with this geometry. In our system, failure is defined as an effluent turbidity of above 1 NTU. We achieved an acceptable effluent turbidity with a 15.1 mm diameter tube that had a length of 30.5 mm. With the good experimental results, we then subjected this tube settler to varying alum dosage to investigate the affect of dosing on tube settler performance. At each alum dosage, the tube settler was tested at a variety of capture velocities and at two different floc blanket levels: the lower level is when the height of the floc blanket falls below the bottom of the tube settler, the high floc blanket level is when the floc blanket height is above that of the bottom of the tube settler.
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Experiment 5: Alum Dose = 105 mg/L
Process Controller Files
Figure 1: Capture Velocity vs. Average Effluent Turbidity shown for each alum dose at low floc blanket level.
Figure 2: Capture Velocity vs. Average Effluent Turbidity shown for each alum dosage at high floc blanket level.
Conclusions
Overall, this system performed well and most of the effluent turbidities were below 1 NTU. The thesis on evaluation on parameters affecting steady-state performance of a floc blanket found that the ideal dosage was 45 mg/L for 100 NTU influent water. The alum doses of 35 mg/L and 65 mg/L performed best. Because the slight underdose and overdose peformed well (average effluent turbidities were under 1 NTU), what was thought to be extreme under and over doses were also tested. We tested 15 mg/L and 105 mg/L to observe how the floc blanket formed under severe non-ideal conditions. The dose of 105 mg/L, despite averaging at less than 1 NTU, resulted in failure since the average effluent turbidity frequently spiked above 1 NTU. The 15 mg/L dose, however, had average effluent turbidity of less than 1 NTU, meaning that cannot be considered a failure.
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