Please note that the average effluent value from the 15.1 mm tubes at the high floc blanket at the lowest critical velocity is questionable...this value is not included in Figure 1 (the graph) below and we should consider doing that trial again. do we have the data for the 12 mm tubes?
Methods
To determine the effects of inner-diameter, flow rate, and floc blanket height on settling efficiency, we 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 experiment.
Table 1. Parameter table.
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To begin, we observed a "rolling" movement of the floc as it travels up the tube. insert keen insight here. This movement can begin to be described by a quantitative drag analysis ...insert any additional observations here or change "a few interesting observations" above to "an observation of drag"which is in the process of being completed. It is hypotheiszed that the flocs in the smaller diameter tubes experience enough drag force tooverpower the settling force due to gravity.
The wider tube settlers, as expected, provided slightly more sensitive data. That is, the effluent turbidity was measurably impacted by changes in flow rate, floc blanket height, and tube diameter. The table and graph below illustrate the average effluent turbidity for the three diameters described in the methods section above.
Table 2. Results
_Figure 1. Results
Table 1. Parameter table.
These results are displayed graphically below.
_Graph 1. Effluent Turbidity vs. Critical velocity
!PSSAvgEffTurb vs Vc.jpg |width=700px height=1200px!Figure 1. Results
As the results show, the second lowest capture velocity for each diameter tube resulted in the optimum settling efficiency at the low floc blanket heights. The results also show a general trend of increasing effluent turbidity once the capture velocity exceeds 11.0 m/day. This indicates that the capture velocity designed to in the current plants is appropriate.
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what are the newest small tube data? this data could probably be reworked to fit better.
_The plot below displays the effluent turbidity vs. critical velocity graphed on a semi-log plot. Each flow state was run for 6 hours, however, the floc blanket was at the high setting of 60 cm, as opposed to the desired low setting, due to air blocking the flow through the solenoid valve. There were also error in both the initial calculations of the flow rate and the tubing size. Instead of testing at a Vc range of 5 to 20 m/day a much higher Vc range of around 39 to 131 m/day. The results are display in the graph below.
Graph 1 The average effluent turbidity of the 9.5 mm tubes at a high floc blanket, with very high Vc values.
The graph clearly indicates that at the first Vc, the 9.5 mm tubes performed very well, with effluent turbidities around 0.5 NTU. The next three Vc settings result in very high effluent turbidities, over 100 NTU over the influent. This high values are most likely cause by a combination of extremely high Vc and the tubes position in the floc blanket at the upper height of 60 cm._
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