Lamella Sedimentation Tank

Abstract

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h5.Aerial View of the Parallel Sedimentation Tanks
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The Lamella Sedimentation Tank design was design to test different variables, such as lamella spacing, lamella length and joint performance with sludge blankets, that can affect the overall sedimentation process. These variables are being test the limits of our design.

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The same tank size was used for the lamella design as was used for the floc blanket design. The lamella were designed to be constructed in a grid because a material with a set baffle spacing of 11mm was thought a possible material. In this suggested grid set-up a series of channels of 11mm by 7mm in cross section would be set into the tank, this was done to ensure that a V _up of close to 100 m/day was met. If the lamella were adjusted to be parallel plates that extended the width of the channel (the current agauclara AguaClara design) then the baffles would have to placed much closer to each other to guarantee a V _up of 100 m/day.

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The first step in the lamella design was to determine the size of the lamella needed. A method very similar to the one used to determine the correct pipe size for the effluent launder was used to find length of the lamella. The equation for lamella length is implicit and thus the correct length was iteratively determined.
The implicit equation used can be seen below:

The following two equations were substituted into the above main equation.
Number of lamella sheets needs to fill the tank:

The number of cells in on sheet of lamella given the tank size:

The target V _up value was 100 m/day. This was left constant instead of being updated with each iteration. This was done because the program would not converge otherwise. After the program returned the converging value of Lamella Length, the active upward velocity and critical upward velocity needed to be calculated. The active upward velocity is different from the target upward velocity because the dead zone created from the lamella angle has to be taken into account. The active length of Lamella, active upward velocity and critical velocity were calculated using the following equations:

The initial program of used to determine the lamella length returned the total length of the material placed at an angle of 60 degrees. For construction uses and determination of the inlet position we needed to determine the vertical height of the lamella. For this calculation the follow was used:

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