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B Exam: Sedimentations

front 1

How many zones are there in a sedimentation tank?

back 1

4

front 2

Which is the largest zone in a sedimentation tank?

back 2

Settling Zone

front 3

In a conventional sedimentation tank, how long is the detention time?

back 3

2-6 hours

front 4

What is short-circuiting?

back 4

When water takes a direct path from the influent to the effluent without fully mixing with the contents of the tank.

front 5

What do you call the 4 zones in a sedimentation tank?

back 5

Inlet, Settling, Sedimentation or Sludge, and Outlet

front 6

What affects the settling process?

back 6

Temperature and Turbidity

front 7

What are the advantages of a solid contact unit?

back 7

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.

front 8

For the volume over volume test, a ______ sample is taken from the ______ zone, and allowed to settle for ______ minutes?

back 8

Ans. 100 mL, reaction zone, and 5 minutes

front 9

What advice can you give to an operator at a neighboring plant who is experiencing high chemical costs?

back 9

Recirculate chemicals.

front 10

When you took sludge samples, you determined that there was too much sludge in the tank. What will you do to correct this problem?

back 10

Increase the number of blow downs or increase the duration of the blow downs, or both

front 11

Observation of the treatment process indicated that there is not enough sludge in the treatment tank. What action is needed?

back 11

Reduce the number of blow downs or their duration/ adjust the recirculation rate

front 12

How do you adjust the recirculation rate?

back 12

Increase or decrease the flow (Some solid-contact units have a sludge recirculation device)

front 13

By ______ the recirculation rate, a ______ amount of sludge will be held in the tank.

back 13

Increasing, Larger

front 14

If the recirculation rate is too high, ______ will be carried over to the ______

back 14

Sludge slurry, filter

front 15

How are the bottoms of sedimentation tanks and solid-contact units configured to aid in sludge removal?

back 15

They are sloped toward the center

front 16

What would you install to improve sedimentation?

back 16

Tube Settlers

front 17

What affects the efficiency of tube settlers?

back 17

High Winds

front 18

The gathering of a liquid or dissolved substance on the surface or interface zone of another material is called?

back 18

Adsorption

front 19

An electrical system for the preventing of rust or corrosion of metal surfaces that are in contact with water is called?

back 19

Cathodic Protection

front 20

In direct filtration, what process is omitted?

back 20

Sedimentation

front 21

A water treatment process in which solid particles settle out of water being treated is called?

back 21

Sedimentation

front 22

Put these processes in their correct order - flocculation, filtration, sedimentation, and coagulation.

back 22

Coagulation, flocculation, Sedimentation, and Filtration

front 23

How do you prevent short-circuiting?

back 23

Install Baffles

front 24

If an over dose of coagulant occurs, what happens in solids-contact tank?

back 24

Sludge settles too rapidly, and there is not enough sludge slurry recirculated

front 25

How many sedimentation basins or solid contact units are needed in a WTP?

back 25

2

front 26

How does the operator of a solids-contact unit control the performance of the unit?

back 26

Adjusting the chemical dosage, recirculation rate, and sludge control

front 27

A solid contact unit has a surface-loading rate of 0.95 GPM/sq ft. What is the rise rate in feet per minute?

back 27

front 28

What factors control the detention time?

back 28

Flow and Tank Volume

front 29

Lower temperatures cause what condition in solids-contact tank?

back 29

Slow settling

front 30

Solids-contact units are most unstable during what conditions?

back 30

During rapid changes in temperature, flows and turbidity

front 31

When there is a large increase in turbidity of the flow to a solids-contact unit, what action is needed?

back 31

Ans. Jar Test
Ans. Increase Coagulant dosage
Ans. Change coagulant
Ans. Increase alkalinity
Ans. Adjust Flash mixer/flocculator speed/intensity

front 32

What will happen if the recirculation rate is too low?

back 32

Sludge will settle to fast and there will not be enough sludge recirculating

front 33

How is pin floc removed?

back 33

Ans. Filtration
Ans. Recarbonation

front 34

What is the best test to evaluate the water treatment processes?

back 34

Turbidity

front 35

What is the best way to control chemical feed rates/dosages n a WTP

back 35

Electronically Controlled Chemical Feeders

front 36

A WTP is having problems maintaining its sludge blanket. What action is needed?

back 36

Adjust recirculation rate

front 37

A water treatment solids-contact unit is 75 ft long25 ft wide and 10 feet deep. What is the surface loading rate of the tank at a flow 6.5 MGD during the 3PM to 11 PM shift

back 37