Sedimentation Tank Hydraulics
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Introduction
A floc blanket is a dense, fluidized bed of particles that forms in the sedimentation tank below the plate settlers. A floc blanket works like a mesh to trap small flocs, thereby reducing effluent turbidity. As flocs are continually resuspended in the blanket, sludge build up on the tank bottom is reduced. The sedimentation needs to be drained and cleaned less frequently, reducing the amount of clean water wasted.
The latest working design of the AguaClara sedimentation tank consists of an inlet manifold with vertical diffusers to channel water into the tank as a line source. A semi-circular half-pipe beneath the diffusers serve as a jet reverser to resuspend flocs. Plate settlers placed above the inlet manifold that catch flocs while allowing water to flow past the settlers into exit launders. The flocs that settle out at the bottom of the sedimentation tank are removed regularly by a sludge drain. Implementing a floc blanket and a floc hopper in the sedimentation tank provide an additional method of filtration and will reduce sludge build up, instead allowing flocs to be wasted at a constant rate from the floc hopper.
Current and Future Research
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One of our main goals of the semester was switching our coagulant to PACl instead of alum and see how the change affects performance. The PACl seemed to be much stickier than alum and we had problems with it sticking to the glass and insides of the flocculator. We also conducted experiments switching energy dissipation rates in the jet reverser. We were expecting to find a point where the energy dissipation rate is too high and performance decreased. We didn’t find a point where the floc breakup caused a decrease in performance. During these tests we actually found that momentum can play a large role in floc blanket failure because if the momentum of the floc sliding down the incline gets too large it can overpower the pet reverser and cause it to fill up. We also looked at sludge consolidation depending on the depth of the floc hopper. We found that the depth can make a large difference in consolidation. |
More Information
Sedimentation Team Research Rationale
Sedimentation Team Research Rationale2
Sedimentation Team Research Report 1
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| h1. Inlet Manifold Research Team
h2. Introduction
The design challenge for the Inlet Manifold Research Team is to design an inlet manifold for the sedimentation tank that meets the following constraints:
* Maintain the velocity of the water high enough to prevent sedimentation prior to the tank
* Obtain an even distribution of the influent along the length of the sedimentation tank
* re-suspend the flocs in the bottom of the sedimentation tanks to promote a floc blanket
* prevent floc breakup
* test the theories of manifold flow and the effects of pressure recovery
The inlet manifold consists of a PVC pipe with a row of drilled holes facing down. The jets coming out of the ports will prevent floc accumulation in the bottom of the sedimentation tanks and hopefully the velocity will keep the floc in suspension to create a floc blanket.
Read more about the inlet manifold [design|Agalteca Design]. If you are new to the project, please check out the current [challenges|Future Challenges Inlet Manifold]. Included are our team's [detailed task lists|Detailed Task List Inlet Manifold] for further information.
h2. Manifold Theory
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h5. Figure 1: Hydraulic Gradeline and Energy Gradeline profiles for an Inlet Manifold
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By looking at this image on the right, we can observe that as the water runs through the manifold, the Hydraulic Grade Line (HGL) decreases due to major head losses (friction losses along the pipe walls). But, as the water passes each port and the flow inside the manifold decreases, the velocity inside the manifold decreases as well. As a consequence we should observe a decrease in the HGL slope after each port.
But the most interesting aspect of this study, is that as the velocity decreases we will have a pressure increase after each port (refer to eq-1 on [theoretical information about manifolds|Inlet Manifold Equations]), which leads to an HGL increase, if we keep the elevation constant, as is the case.
This is what we call pressure recovery\!
Considering the major head loss along the manifold is small, due to the low velocities we have to prevent floc breakup,these local HGL increases will have a big impact in the overall HGL shape and we expect to have a higher HGL at the end of the manifold than at the beginning, and therefore a higher flow in the last ports.
Stay up-to-date on this project by checking
the [Meeting Minutes|Inlet Manifold Meeting Minutes], [goals|Inlet Manifold Goals] and [Challenges for Future Semesters|Inlet Manifold Future Challenges].
h2. Current Research Teams
[Spring 2010 Inlet Manifold Research Team|Spring 2010 Inlet Manifold Research Team]
* Redesigning the inlet manifold for the sedimentation tank in an effort to maintain constant flow out of all of the ports.
[Spring 2010 PIV Research Team|Spring 2010 PIV Research Team]
* Measuring energy dissipation in a model flocculator using particle image velocimery. |
