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33 Cards in this Set
- Front
- Back
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What are the purposes of the sedimentation process? |
To remove suspended solids that are denser than water To reduce the load on the filters |
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How is sedimentation accomplished? |
By decreasing the velocity of the water below the point where it can transport settleable suspended material |
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What are the nine factors that affect particle settling in a sedimentation basin? |
Particle size and distribution, shape of particles, density of particles, temperature of water, electrical charge of particles, dissolved substances in water, flocculation characteristics of the suspended material, environmental conditions, sedimentation basin hydraulic and design characteristics |
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What are the four zones of a typical sedimentation basin? |
Inlet zone, settling zone, sludge zone, outlet zone |
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What are launders? |
Skimming or effluent troughs used to uniformly collect settled water Adjustable v-notch weirs are generally attached to the launders for controlling the water level in the sedimentation basin |
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Why are rectangular sedimentation basins often preferred over circular basins? |
Circular basins are more sensitive to short circuiting and achieve poorer solids removal |
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During the operation of a solid's contact unit, what items should be of particular concern to the operator? |
Control of chemical dosages, recirculation rate, control of the sludge blanket |
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List the three advantages of solids contact units |
1. Only one reaction unit to contend with 2. Ability to accumulate slurry during periods of severe taste and odor problems 3. Use slurry accumulation to carry plant when coagulation fails because of increased algal activities |
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How can the level of the slurry or sludge blanket be determined in solids contact units? |
By sampling taps that are placed at various depths on the wall of the solids contact reactor |
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How is the proper chemical dose selected when operating a solids contact unit? |
Jar test |
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List the devices that may be used to provide recirculation in a solids contact unit |
Impellers, turbines, pumping units, air injection |
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How can the depth of sludge in a sedimentation basin be measured? |
Sludge blanket sounder (most common) Bubbler tube Aspirator Ultrasonic level indicator (SUBA) |
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The performance of sedimentation basins depends on what two factors? |
Settling characteristics of the suspended particles Flow rate through the basin |
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What items should an operator monitor during the normal operation of the sedimentation process? |
Turbidity of influent and effluent water Temperature of influent water only Turbidity=in+out Temperature=in only |
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In the routine operation of the sedimentation process, what types of records should be maintained? |
1. Influent and effluent turbidity and influent temperature 2. Amount of water processed and volume of sludge produced 3. Process equipment performance |
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In the sedimentation basin, what problems can be created by a sudden increase in settled water turbidity? |
Floc carryover from the basin will cause premature clogging of filters and will degrade filtered water quality |
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What are the major means by which operators can control water treatment processes? |
By adjusting chemicals and chemical feed rates |
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What should the operator do when source water turbidity levels are increasing rapidly? |
Verify the effectiveness of the coagulant chemicals and dosages being applied at the flash mixer |
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What types of pre-sedimentation facilities are used to reduce the solids removal load on the treatment plant? |
Debris dams, grit basins, impoundments (DIG) |
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What types of currents are found in the sedimentation basin? |
Density currents, Eddy currents, surface currents |
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What are the advantages of an inlet baffle wall? |
Minimize density currents due to temperature differences, minimize short circuiting, minimize wind currents a.k.a. surface currents |
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What chemicals can and operator add to water to cause sufficient alkalinity to be present for coagulation? |
Calcium hydroxide a.k.a. lime Sodium carbonate a.k.a. soda ash Sodium hydroxide a.k.a. caustic soda |
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What do water treatment plant sludges mainly consist of? |
Alum |
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What is the simplest device used to measure the depth of accumulated sludge in a sedimentation basin? |
Sludge blanket sounder |
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What is the detention time for sedimentation basins? |
3+ hours (in the settling zone) |
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What are the characteristics of double-deck basins? |
-They provide 2x the sedimentation surface area of a single basin -they have higher operation and maintenance costs |
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What 3 changes are solids contact units sensitive to? |
Influent flow Temperature of water Turbidity (TIT) |
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How can the percentage of slurry in a solids-contact unit be measured? |
By performing a volume over volume test (V/V) |
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How does the operator of a solids-contact unit maintain the correct slurry volume? |
By controlling the rate of recirculation |
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What percentage of floc will settle out in the first third of the sedimentation basin? |
50% |
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What turbidity levels are considered low for source waters? |
10 NTU or less |
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If floc is coming over at the ends of the basin, it could indicate the possibility of what 4 problems? |
1. Density currents 2. Short circuiting 3. High flows 4. Sludge blankets that are too deep |
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Where in the sedimentation basin is the sludge zone located? |
The bottom of the basin |
