Page History

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Secondary Outlet from the Flocculator
The flow rate of the sedimentation tank is designed to be 24 .5 L/min, but the plant flow rate is designed to be 100 110 L/min. This means that excess flow needs to bypass the sedimentation tank and go directly to the outlet. A large outlet weir is our proposed design for the alternative exit. Because the head loss out of the sedimentation tank is so relatively high (44.979cm5cm through the manifold) the height of the water in the tank versus the weir height is assumed negligible(on the order of mm).

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Where Cw is a constant (equal to 0.611+0.075*(H/Pw) where H is the height of water above the weir and Pw is the weir height), Q weir is the plant flow rate minus the sed flow rate, and the available perimeter was set to be 120 cm. In order to minimize changes in the floc tank the perimeter will be established by cutting a pipe laterally and letting water flow over the the cut out, down into the trough and then out the existing 3" outlet. When this was calculated we got a water height above the weir of 27.12 cm6 mm, which is small enough when compared to the head loss in the launder to assume that it will not affect the flow rate into the sed. sedimentation tank.

Hopper Design for Sludge Blanket
Given the calculated amount of sludge that was calculated the tank would 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 (0.004016) 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 20 mL/min. Therefore, the rate of sludge build-up is the flow rate of alum times the ratio of the sed flow rate to the plant sedimentation flow rate times PhiFloc.

When calculated, the sludge rate volume accumulated over two days was determined to be 31.429 105 x 10^-3 10^3 L/min. Therefore, the minimum hopper volume should be equal to the sludge rate times 48 hours, or 99 cm^2. We have decided to create this hopper with a conical funnel with flex-hose connected at the bottom. This small funnel will continuously drain sludge out of the tank and into the outlet panel. The hose will be 2m long and 1/2" in diameter. The diameter was determined using the manifold equation used in the design of the effluent launder design.

Plant Leveling Tank
The Plant plant leveling tank will handle the outflow from both the sludge blanket tank and the plate settler tank. Using one leveling tank and identical inlet and outlet piping for the two tank ensures identical flow (assuming that the head loss through the tanks themselves are negligible). We decided to make the head loss into the leveling tank the dominant head loss through the system, which then sets the flow rate through the sed sedimentation tanks. Our design for the outflow system was an elevated 3'' pipe with an orifice set into the pipe below the water level. Using the orifice equation, with the flow set at 24 .5 L/min, and using a predetermined safety factor of 18, a desired head loss of 13.673cm was found by multiplying the height of water over the weir in the floc tank head variability by a predetermined safety factor of 12, we could find the required orifice sizethe safety factor. This head was used to determine the orifice size (7/8"). The orifice equation used was the same as used for the flocculator outlet but converted to a circular perimeter from a rectangle.

Tank Drainage Manifold
In order to allow for the entire tank to be drained of water quickly a tank drainage system was established. This system was designed to be very similar to tank tank systems used in Honduras. The set is basically equivalent to the effluent launder except this manifold is located at the bottom of the tank. Flow rate was set to allow the tank to drain in 30 minutes.

This flow rate was established to be 19.425 L/min.
By the same method as was used for the tank effluent manifold the manifold diameter was determined to be 0.75" and the orifice diameter is 9/64".

• The available head the available head for the sludge ports is the total water depth (33.25") minus the head loss in the manifold and minus the velocity head at the end of the manifold.
• Kminor was assumed to be 0 in the manifold and 0.63 in the orifices.
  *Qratio = 0.90
• 15 orifices were assumed to be uniform with the effluent manifold.

Results

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 will Lamella

The same tank size was used for the lamella design was 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.

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

Conclusions