WTO Sedimentation and Filtration 2

Question 1

What is the primary purpose of tube settlers installed in a sedimentation basin?

Accepted Answer

Reduce effective settling depth to improve particle removal

Answer

Increase flow velocity through the basin

Answer

Add coagulant chemicals to the water

Answer

Aerate the water before filtration

Question 2

A rapid sand filter is backwashed when head loss reaches approximately what level above the clean bed loss?

Accepted Answer

5–8 feet

Answer

1–2 feet

Answer

15–20 feet

Answer

25–30 feet

Question 3

Which phenomenon causes a settled floc layer to resuspend and carry over the effluent weir during high flow periods?

Accepted Answer

Sludge blanket upset

Answer

Density currents

Answer

Short-circuiting

Answer

Weir loading excess

Question 4

The Hazen-Williams equation is used in filtration systems primarily to calculate:

Accepted Answer

Head loss through filter media

Answer

Chemical dosing rates for coagulation

Answer

Settling velocity of discrete particles

Answer

Turbidity removal efficiency

Question 5

In a dual-media filter, anthracite coal is placed on top of sand because:

Accepted Answer

Coal has a lower specific gravity and larger grain size, allowing it to remain on top after backwash

Answer

Coal is cheaper than sand

Answer

Coal removes taste and odor compounds

Answer

Sand is too fine to be placed on top without washing away

Question 6

What condition is indicated when a filter's turbidity breakthrough occurs early in the filter run, shortly after returning to service?

Accepted Answer

Filter ripening is incomplete or improper backwash

Answer

Media is too deep

Answer

Backwash rate was too low

Answer

Coagulant dose was too high

Question 7

Weir overflow rate (WOR) in a sedimentation basin is expressed in units of:

Accepted Answer

Million gallons per day per linear foot of weir

Answer

Gallons per minute per square foot

Answer

Nephelometric turbidity units per day

Answer

Pounds of solids per square foot per day