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Each tube settler functioned in as an isolated pair of lamella in the sedimentation tanks. In order to mimic the design of the lamella in the Cuatro Communidades plant the tube settlers were designed to rest at a sixty degree angle, alpha, and with a critical velocity, V alpha, of 10 m/day. The critical velocity of the tube settler determines the size of the smallest floc that is able to settle out in the tube settler.
The critical velocity is calculated by the equation:
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\large
$$
V_c = {{DV_\alpha } \over {\sin \alpha (L\sin \alpha \cos \alpha + D)}}
$$ |
where:
- V c is the critical velocity
- D is the tube settler diameter
- L is the length of the tube settler
is sixty degreesLatex
is the velocity in the tube settlerLatex
The tube settlers were designed to siphon water from the flocculator. Water settled out in a PVC pipe and passed into a small flexible tube from which it was collected. The flow rate was controlled by the height difference between the tube settler outlet and the water level in the flocculator using the equation:
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\large
$$
h = {{V_{siphon}^2 } \over {2g}} - {{V_\alpha ^2 } \over {2g}} + h_l
$$
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where:
- h is the height difference used to control the siphon
- V siphon is the exit velocity of the clear tube
is the velocity in the tube settlerLatex - h l was the head loss in the entire system
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