How many zones are there in a sedimentation tank?
4
Which is the largest zone in a sedimentation tank?
Settling Zone
In a conventional sedimentation tank, how long is the detention time?
2-6 hours
What is short-circuiting?
When water takes a direct path from the influent to the effluent
without fully
mixing with the contents of the tank.
What do you call the 4 zones in a sedimentation tank?
Inlet, Settling, Sedimentation or Sludge, and Outlet
What affects the settling process?
Temperature and Turbidity
What are the advantages of a solid contact unit?
Save on land use, all processes take place in one tank, save on chemicals, ability to adjust the slurry, especially to deal with algal problems, capital and maintenance costs are reduced.
For the volume over volume test, a _________ sample is taken from the__________ zone, and allowed to settle for _____ minutes?
100 mL, reaction zone, and 5 minutes
What advice can you give to an operator at a neighboring plant who is experiencing high chemical costs?
Recirculate chemicals.
When you took sludge samples, you determined that there was too much sludge in the tank. What will you do to correct this problem?
Increase the number of blow downs or increase the duration of the
blow
downs, or both
Observation of the treatment process indicated that there is not enough sludge in the treatment tank. What action is needed?
Reduce the number of blow downs or their duration/ adjust the recirculation
rate
How do you adjust the recirculation rate?
Increase or decrease the flow (Some solid-contact units have a sludge recirculation device)
By _________ the recirculation rate, a __________ amount of sludge will be held in the tank.
Increasing, Larger
If the recirculation rate is too high, __________ will be carried over to the __________.
Sludge slurry, filter
How are the bottoms of sedimentation tanks and solid-contact units configured to aid in sludge removal?
They are sloped toward the center
What would you install to improve sedimentation?
Tube Settlers
What affects the efficiency of tube settlers?
High Winds
The gathering of a liquid or dissolved substance on the surface or interface zone of another material is called?
Adsorption
An electrical system for the preventing of rust or corrosion of metal surfaces that are in contact with water is called?
Cathodic Protection
In direct filtration, what process is omitted?
Sedimentation
A water treatment process in which solid particles settle out of water being treated is called?
Sedimentation
Put these processes in their correct order - flocculation, filtration, sedimentation, and coagulation.
Coagulation, flocculation, Sedimentation, and Filtration
How do you prevent short-circuiting?
Install Baffles
If an over dose of coagulant occurs, what happens in solids-contact tank?
Sludge settles too rapidly, and there is not enough sludge slurry recirculated
How many sedimentation basins or solid contact units are needed in a WTP?
2
How does the operator of a solids-contact unit control the performance of the unit?
Adjusting the chemical dosage, recirculation rate, and sludge control
A solid contact unit has a surface-loading rate of 0.95 GPM/sq ft.
What is the
rise rate in feet per minute?
What factors control the detention time?
Flow and Tank Volume
Lower temperatures cause what condition in solids-contact tank?
Slow settling
Solids-contact units are most unstable during what conditions?
During rapid changes in temperature, flows and turbidity
When there is a large increase in turbidity of the flow to a solids-contact unit, what action is needed?
Ans. Jar Test
Ans. Increase Coagulant dosage
Ans. Change
Coagulant
Ans. Increase alkalinity
Ans. Adjust Flash
mixer/flocculator speed/intensity
What will happen if the recirculation rate is too low?
Sludge will settle to fast and there will not be enough sludge recirculating
How is pin floc removed?
Ans. Filtration
Ans: Recarbonation
What is the best way to control chemical feed rates/dosages n a WTP?
Electronically Controlled Chemical Feeders
A WTP is having problems maintaining its sludge blanket. What action is needed?
Adjust recirculation rate
A water treatment solids-contact unit is 75 ft long, 25 ft wide and 10 feet deep. What is the surface loading rate of the tank at a flow 6.5 MGD during 3 PM to 11 PM shift
