Sedimentation Tank Hydraulics
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h4. Sedimentation Tank Hydraulics
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h5. Introduction
A floc blanket is a dense, fluidized bed of particles that forms in the sedimentation tank below the plate settlers. A floc blanket helps to reduce effluent turbidity by trapping small flocs and reduces clean water waste through less frequent draining of the sedimentation tank.
The current design of sedimentation tanks in Agua Clara plants consists of plate settlers placed above the inlet manifold that catch flocs formed in the flocculator while allowing water to flow past the settlers into exit launders. The flocs then settle out at the bottom of the sedimentation tank and 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.
h5. Current and Future Research
We wish to determine optimal bottom geometry of a sedimentation tank for floc blanket formation. Floc resuspension is necessary for floc blanket formation so that flocs are recirculated through the tank instead of settling on the tank bottom as sludge. For adequate floc resuspension to occur, flocs settling in the sedimentation tank must be directed towards the path of the jet via an incline. We are examining mechanisms for floc resuspension for various bottom geometries by studying the relationships between hydrostatic pressure of solids built up on the sedimentation tank incline and and hydrodynamic pressure of the jet. We are also looking at parameters such as floc blanket formation time, clarified effluent turbidity, and tube settler turbidity for various bottom geometries, which will help us to determine the optimal bottom geometry given a specific design objective.
Our team is also working on designing a floc weir for the sedimentation tank, which will waste flocs at a constant rate from the floc hopper and serve to keep the floc blanket at a constant height.
h5. More Information
[Challenges Sedimentation Spring 2011]
[Sedimentation Team Detailed Task List]
[Sedimentation Team Research Rationale]
[Sedimentation Team Research Rationale2]
[Sedimentation Team Research Report 1]
[Sedimentation Team Final Research Report]
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h6. Members
[Mahina Wang|mgw56]
[Jill Freeman|jef246]
[Saied Khan|sak332]
[Yiwen Ng|Yiwen Ng's Individual Contribution Page]
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h6. [Sedimentation Tank Hydraulics Documents]
| | Challenge | Tasks | Teach in | Final Presentation | Final Report |
| Spring '12 | [!Research^pdf_icon.jpg|height=25!|^STH Design Challenges SP 12.pdf] | [!Research^pdf_icon.jpg|height=25!|^STHT Detailed Task List SP12.pdf]| | | | |
| Fall '11 | | [!Research^pdf_icon.jpg|height=25!|^Detailed Task List 1.pdf] | [!Research^ppt_icon.jpg|height=25!|^Fall 2011Teach In w.o videos.pptx] | [!Research^ppt_icon.jpg|height=25!|^Final Presentation Fa 11.pptx] | [!Research^pdf_icon.jpg|height=25!|^Final Report Fa 2011.pdf] |
| Summer '11 | | | [!Research^ppt_icon.jpg|height=25!|^Teach In.pptx] | [!Research^ppt_icon.jpg|height=25!|^Final Presentation Summer 2011.pptx] | [!Research^pdf_icon.jpg|height=25!|^finalreport_sedtankhydSummer2011.pdf] |
| Spring '11 | [!Research^word_icon.jpeg|height=25!|Challenges Sedimentation Spring 2011] |[!Research^word_icon.jpeg|height=25!|Sedimentation Team Detailed Task List] | [!Research^ppt_icon.jpg|height=25!|Sedimentation Tank Hydraulics^SedimentationTankHydraulicsTeachInSpring2011.ppt.pptx] | [!Research^ppt_icon.jpg|height=25!|Sedimentation Tank Hydraulics^SedimentationTeamHydraulicsFinalPresentation.pptx] | [!Research^word_icon.jpeg|height=25!|Sedimentation Team Final Research Report] |
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h6. Past Research
[Fall 2010 Inlet Manifold Team]
[Spring 2010 Inlet Manifold Research Team]
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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
