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Please note that the data average effluent value from the 15.1 mm tubes at the high floc blanket was a convincing outlier..it's data are at the lowest critical velocity is questionable...this value is not included in the results section below and we should consider doing that trial again.
Methods
In order to To determine the effect effects of the inner-diameter of the tube settlers , flow rate, and floc blanket height on settling efficiency, a three-part experiment was completed to vary flow rate, inner tube diameter, and tube inlet location. A range of flow rates were run through the tube settlers, with inlets both in and above the floc blanket, with a range of diameterswe completed an experiment to vary these three parameters. Based on the two-inch lamella spacing currently used in AguaClara plants, we chose a range of diameters less than two-inches to push the lower-limit of lamella spacing. Similarly, the range of flow rates that we tested was based on the current capture velocity used in the plants. The final variable in this experiment, the floc blanket height, was set to both fully submerge the inlet of the tube settlers and to leave the inlets resting above the top of the floc blanket. Table 1 below illustrates the parameters for the proposed experiment.
The diameters of the tubes were chosen to explore a range of spacings based on the current plate spacings used in plants of two inches. The flow rates were chosen to explore a range of capture velocities from 5-20 m/day.
Table 1. Critical velocity Parameter table.
As described on our apparatus design page, this experiment used the process controller program to automate the system. The main process controller states for the experiment were floc blanket formation, two flow states for high and low floc blanket heights, a floc blanket equilibrium state, and two states devoted to incrementing the flow rates. Several other states, such as drain, were used for system maintenance.
Results
This experiment has led to a variety of observations and quantitative results.
We expect to see failure in the lower diameter tubes with the high Vc values because the flocs have a smaller area over which they can settle. The smaller diameters are expected to with flocs more quickly, and are less likely to have flocs waste out of the tube as the flow state is running.
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