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11 Cards in this Set
- Front
- Back
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What is the purpose of settling tanks? |
To remove particles that would otherwise rapidly clog the filters during filtration |
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What are the 4 zones of a clarification basin? |
1) inlet zone 2) settling zone 3) sludge zone 4) outlet zone |
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What is type 1 sedimentation? |
Settling of discrete or individual particles with a constant settling velocity vs. They do not flocculate or stick to other particles in the tank. (E.g sand or grit) |
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What influences settling efficiency of type 1? |
1) particle density 2) particle size 3) temperature ( lower temps= slower settling) 4) turbulence (higher turbulence= slower setting) 5) bottom scour (can resuspend settled particles) 6) Coagulation and flocculation (larger particles settle faster) |
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What is type 2 sedimentation? |
Sedimentation by particles that flocculate during sedimentation with their size constantly changing so settling velocity constantly changes (Think settling column) |
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What is type 3 sedimentation? |
Or zone sedimentation- particles at a high concentration settle as a mads and a distinct clear zone and sludge zone are present - more prevalent in wastewater treatment |
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What is type 4 sedimentation? |
At high concentrations of solid the particles are in contact and further settlement is by the weight of particles above them |
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Discuss rectangular setting basins |
+simplest design, large scale, stable and predictable, cost effective, low maintenance and power consumption - large area required
L/W=20 is ideal but L/W=(2->5) is acceptable to save space Usually L= 30->100m and W= 6->10m Depth= 2.5->5m and L/H <18 Velocity of flow is not greater than 0.3m/s to avoid scouring Bottom is slightly sloped to facilitate scouring |
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Describe Circular settling basins |
Particle path is a parabola +less dead space, cheaper to build - corner sweeps are difficult, shorter distances for settling to occur, high upkeep and maintenance
Diameter = 20->40m Depth= 2.5->5m |
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Describe a sludge blanket clarifier |
Coagulation, flocculation and clarification occur all in different sections of the same tank Chemicals and water are mixed in the centre cone like structure (coag and floc) Solids flow down the cone and settle into a sludge blanket When the level of the sludge blanket rises above a specified level, the sludge spills into waste sludge concentrators The top of the sludge blanket must be well below the top water level of the tank otherwise considerable quantities of floc will be carried into the outlet +reduced size of unit - more maintenance |
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What is dissolved air filtration? (DAF) |
Particles are removed on the surface instead of at the bottom after settling A small flow of micro bubbles air lift flocs to the surface +3% solid sludge compared to 0.5% for other clarifiers + requires a small area - more power required for air compressors - inefficient in cold water L/w >1 L<11m to maintain bubbles Depth <2.5m |
