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By running the ramp state function on different tube settler diameters, we hope to further develop the relationship between plate settler size and floc roll up.
Experiment 1: Ramp State with 9.5 mm Plate Settler Tube Diameter
This experiment starts with a flow rate of 6 mL/min and over the course of 24 hours, gradually increases to a flow rate of 50 mL/min. This flow rate range corresponds to a capture velocity range of approximately 11 m/day to 91 m/day.
Figure 1: Effluent Turbidity vs. Flow Rate
Experiment 1 Conclusions
The very clear spike in the data represents the point at which the floc particles began to roll up the tube settler, which was confirmed visually in the experimental apparatus. The velocity represents the critical velocity. At a certain velocity, the turbidity stabilizes, and stops increasing. This is because at a certain point, the number of flocs rolling up in the settler cannot increase anymore, therefore the turbidity cannot increase anymore. Given the current data that has been collected, we are not sure if this curve accurately represents how the turbidity should change during the ramp state function. Futher experiments are being run to confirm this.
Experiment 2: Ramp State Function with 15.3mm Tube Settler Diameter
This experiment starts with a flow rate of 6 mL/min and gradually increases to a flow rate of 140 mL/min over the course of 24 hours. This flow rate range corresponds to a capture velocity range of approximately 11 m/day to 256 m/day.
Figure 1: Effluent Turbidity vs. Flow Rate
Conclusions
Unlike the results for the 9.5mm tube, there isn't a sharp increase in the turbidity which would clearly indicate the critical velocity. Rather, there is a gradual increase in the turbidity, showing that floc roll up is happening, however it is not possible to identify the exact critical velocity from this range of capture velocities tested. Like the 9.5mm tube, the turbidity eventually reaches a plateau, indicating the point at which the maximum amount of flocs are rolling up the tube. The discrepency between the results of the 15.3 mm tube and the 9.5 mm tube is currently being investigated.