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 the results section below and we should consider doing that trial again.
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.
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.
Preliminary experiments were conducted to determine the appropriate time interval for the flow and increment states. 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
As the results above indicate, the nar