Page History

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Hopper Design for Sludge Blanket
Given the calculated amount of sludge the tank will create, a continuous sludge drainage system was created. This was done to decrease the size of the hopper in the tank. It was desired to keep the hopper small so that there would be minimal disturbance in the tank. We created a parameter, PhiFloc, which is the ratio of how much the alum flow rate relates to the the volume of flocs created in a certain amount of time. The value (0.016) was taken from the mathCAD file used to create the ideal Gmax versus Gtheta curve. The majority of a sludge is assumed to be made of alum, and the flow rate of alum is approxamitely approximately 20 mL/min. Therefore, the rate of sludge build-up is the sedimentation flow rate times PhiFloc.

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The first sedimentation tank containing the sedimentation tank has been constructed. Flocs are entering the tank and not breaking up upon entrance so it has been determined that our entrance pipe calculations are reliable. Over the next week we are observing the tank and trying to see how the sludge blanket forms.

Design of the Sedimentation tank

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with Lamella

The same tank size was used for the lamella design was as was used for the sludge blanket design. The lamella were designed to be constructed in a grid versus the plate lamella used in previous designs. This was done to ensure that a Vup of close to 100 was met.

The inlet design, the effluent launder design, tank drain design will all be the same as for the sludge blanket sedimentation tank. The only difference is that the inlet will have to enter the tank below the lamella and thus two 22.5 degree angle bends are to be used to lower the inlet pipe level from where it exits the floc tank to where it needs to enter the sedimentation tank. This tank was designed to be versatile and the lamella placed close enough to the top of the tank to allow for the possibility that a sludge blanket could be formed underneath the lamella if desired.

Lamella Design
The lamella were designed out of corrugated plastic. Flow was designed to move upward through the grid of channels in parallel. The dimensions of the material proposed for use are listed below.

• b = 10.5mm - the distance between corrugations
• w = 6.96mm - the width of the channel (same as the width of the material)
• thickness = 0.40mm - the thickness of the plastic material
• alpha = 60 deg
• epsilon = 0.003mm

The first step in the lamella design was to determine the size of the lamella needed. A method very similar to the 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 Vup value was 100m/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:

Insert equation for active length of lamella.

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:

Conclusions