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