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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.
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.
Preliminary experiments have been conducted for the purpose of determining the Preliminary experiments were conducted to determine the appropriate time interval for the flow and increment states, as well as determining which Vc and floc blanket combination cause failure. Based on these preliminary findings we are modifying the experiment to produce quality results in an efficient manner.. These experiments consisted of running the system for an exorbitant length of time to identify the timeframe necessary to reach constant effluent turbidity. Ultimately, we decided to form the floc blanket for three hours; run each flow rate for six hours; stop effluent flow for ten seconds between flow rates; and allow about twenty minutes for the floc blanket to grow from its low to high depths. The floc blanket was reformed each time a new diameter was tested.
Results
what are the newest small tube data? can you please do the introduction to the results and clean-up this initial data?
_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._
As stated in the methods section above, this experiment primarily tested tube settlers of three diameters.
Conclusions and Future work
From As the preliminary results we were able to troubleshoot many of the errors in the system. Future work includes testing all of the parameters in the above chart at the two floc blanket heights. The results were not conclusive enough to determine the appropriate time interval for the flow states, so we will stick with the 6 hour time period. above indicate, the nar