Primary Treatment

Question 1

If a particle settles at a rate of 0.8 mm/sec what is the minimum detention time required to ensure that the particle is removed from a primary clarifier that is 32
meters long by 6.0 meters wide by 2.88 meters deep?
a) 60 minutes
b) 120 minutes
c) 360 minutes
d) 553 minutes

Answer 1

a) 60 minutes

Question 2

The removal efficiency of a primary clarifier is determined by:

a) The pH, temperature and BOD of the primary influent
b) Detention time, clarifier depth and frequency of sludge removal
c) The use of fibreglass versus wooden flights on the collector mechanism
d) None of the above

Answer 2

b) Detention time, clarifier depth and frequency of sludge removal

Question 3

Three of the most common types of pump used to remove sludge from a primary clarifier are:

a) Air lift, centrifugal, jet
b) Piston, positive displacement screw, centrifugal
c) Peristaltic, diaphragm, vertical turbine
d) Centrifugal, trash, vacuum

Answer 3

b) Piston, positive displacement screw, centrifugal

Question 4

What is the BOD removal efficiency of a primary clarifier if the influent BOD concentration is 200 mg/L, the effluent BOD concentration is 140 mg/L and the HRT is 2 hours?

a) 0.3%
b) 30%
c) 50%
d) 60%

Answer 4

b) 30%

Question 5

Effluent weirs must be adjusted to ensure that flow is dispersed evenly around the perimeter of the tank.

a) True
b) False

Answer 5

a) True