Environmental Engineering Multiple Choice Questions on “Flocculation and Clarification”.
1. __________ is an operation designed to force agitation in the fluid and induce coagulation.
a) Sedimentation
b) Flocculation
c) Disinfection
d) Aeration
Answer: b
Clarification: Flocculation is an agitating process in which destabilized particles are brought into contact to promote agglomeration.
2. The rate of change of velocity per unit distance normal to a section is called_______
a) Mean velocity
b) Average velocity
c) Mean velocity gradient
d) Velocity gradient
Answer: c
Clarification: Mean velocity gradient is given by G = (P/uv)1/2 Where P = power dissipated, u = absolute viscosity, v = volume to which power is applied.
3. What is the dimension formula of mean velocity gradient?
a) 1/T
b) 1/T2
c) T
d) T2
Answer: a
Clarification: Mean velocity gradient is expressed in metre per second/m or Sec-1, so it has dimension formula of 1/T.
4. What is the desirable value of mean velocity gradient in a flocculator?
a) 20-50sec-1
b) 20-75sec-1
c) 50-100sec-1
d) 30-50sec-1
Answer: b
Clarification: The desirable value of mean velocity gradient (G) in a flocculator is 20-75sec-1 and for ‘Gt’ is 2*104 to 6*104 where ‘Gt’ is the ratio of power induced rate of flow to displace mean induced rate of flow.
5. What is the normal value of the detention period adopted in a flocculator for design purpose?
a) 30min
b) 60min
c) 90min
d) 100min
Answer: a
Clarification: The detention period in a flocculator for design purpose should be in the range of 10-40min and its normal value should be 30min.
6. The design value of the velocity of flow in a flocculator is _______
a) 0.2-0.8m/s
b) 0.3-0.5m/s
c) 0.6-0.8m/s
d) 0.1-0.5m/s
Answer: a
Clarification:The normal value of the velocity of flow in a flocculator is 0.4m/s and its range is 0.2-0.8m/s.
7. What is the detention period of a clarifier used in the treatment of water?
a) 1hour
b) 2hours
c) 3hours
d) 4hours
Answer: c
Clarification: The detention period of a clarifier is lower than in the plain sedimentation tank and its range is 2.5 to 3 hours.
8. The pulsator clarifier is a type of __________
a) Horizontal flow sludge tank
b) Vertical flow sludge tank
c) Circular sludge tank
d) Plain sedimentation tank
Answer: b
Clarification: The pulsator clarifier is a vertical flow sludge tank in which pulse is generated at interval of 30Sec to give rapid flow for 5-10Sec resulting in the alternative rising up of the sludge blanket.
9. Which device solved the problem of unstable hydraulic conditions and operation of sludge removal equipment?
a) Centrifugal pump
b) Pulsator clarifier
c) Tube settler
d) Flocculator
Answer: c
Clarification: Tube settler solved the problem of unstable hydraulic conditions and operation of sludge removal equipment by providing laminar flow conditions for sedimentation.
10. In which device, the primary mixing is followed by a secondary reaction zone resulting in formation of sludge blanket?
a) Centrifugal pump
b) Flocculator
c) Tube settler
d) Solid contact clarifier
Answer: d
Clarification: In Solid contact clarifier, sludge blanket is formed where straining action occurs to remove some of the finer particles. The thickness of the blanket is 1m.
11. In which type of tube settler, tubes are slightly inclined in the direction of normal flow?
a) Solid contact clarifier
b) Steeply inclined tube settler
c) Vertical tube settler
d) Horizontal tube settler
Answer: d
Clarification: In Horizontal tube settler, the tubes are slightly inclined in the direction of normal flow and the sludge settled is drained by filter backwash.They are used in small plants.