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--Bucket 1 has the concentrated clay that is being stirred.
--Bucket 2: (1)The gold labeled tube evaluates that the flow is maintained at 100 Ntu by checking the flow with the turbidity meter.
--Turquoise labeled tubing indicates the main flow that leads to the ultimate goal: measuring the plate settling tubes' turbidity.
Design Parameters (parameters/equations/length and diameter values/critical settling velocity values)
The use of a tube flocculator allows for a more controlled flocculation environment as compared to flocculation with baffles. The flocculation design parameters are based on creating optimal conditions for floc blanket formation. For this experimental apparatus the flocculator is 17 m and the inner tube diameter is 3/8 in (see table). The average velocity gradient for the flocculator (G) is 71.4 1/s -1 , the residence time (θ) is 125.4 s and the G θ is 89519.959*103.
These values are found using the following equations:
Average Velocity Gradient
Residence Time
The high G value and long residence time helps create the large amount of flocs needed for the initial formation of the floc blanket. The flow rate through the flocculator (545 mL/min) is separated into two equal flows of 272 mL/min, based on the maximum flow through the peristaltic pumps.
Based on the allowable space in the settling column the floc blanket height will be 50 cm.
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Flow in to the system from the bottom of the settling column creates a jet in the center of the column, which is far from uniform flow. A typical dissipation ratio is 1:10; therefore, it would take on the order of 10 m for jet to dissipate in a column with a diameter 10 cm, as in the current setup. A cone with a ratio of 4:6 is used a diffuse to maximize the lateral spread of the jet. In addition to the cone, there is a mesh directly on top of the cone made of a 1 cm thick plastic sheet with uniformly distributed holes of 0.5 cm diameter. This mesh will break up the single jet coming from the column inlet, into several smaller, weaker jets that will dissipate quicker. The preliminary stages of the experiment will test the effectiveness of the cone and mesh system in dissipating the jet and allowing for optimal floc blanket formation and maintenance.
Based on the allowable space in the settling column the floc blanket height will be 50 cm. The alum dosage of 45 mg/L is also important for the creation of the floc blanket. In previous experiments it was thought that 45 mg/L was too high increasing the "stickiness" of the tube settlers and leading to clogging. The same chemical properties of the aluminum sulfate actually aid in the creation and maintenance of the floc blanket, creating a stick mesh of suspended flocs.
Sedimentation
The sedimentation process, which occurs directly after flow through the floc blanket, is the final separation technique in our water purification system. By the time the water enters the tube settlers, uniform flow has been established and the floc blanket has already dramatically reduced the water turbidity. The design of the sedimentation section of the apparatus requires serious consideration of flow rates, tube geometry, and other parameters.
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