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The sedimentation process, which is completed directly after the floc blanket, is the final separation process of water purification. By the time the water enters the tube settlers, the turbidity has been dramatically reduced by the floc blanket. As seen in the figure below, the apparatus allows for independent control of the flow rates through the floc blanket and the tube settlers because of the additional waste outlet just above the floc blanket. The water flows up through the tube settlers and manifold, through a turbidity meter, and is wasted. This flow is controlled by the same pump circulating alum to the system. In order to maintain a steady flow, a buffer may be utilized.
Settling Tube Schematic
The flow rate is based on a desired upflow velocity of 100m/day through the tube settlers (this number is based on previous pilot plant research). Note that the tubes are at the standard sixty-degree angle from the horizontal. Below is the calculation of the flow rate, regulated by a pump, through the tube settlers.
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