1. Why Magnesium carbonate is not commonly preferred as coagulant?
a) It is expensive
b) It does not remove color
c) Formation of sludge
d) The time required for floc formation is less
Explanation: When magnesium carbonate and lime are dissolved in water, magnesium hydroxide and calcium carbonate are formed which are soluble in water and sludge is formed in slurry form, so they are not commonly used.
2. Which of the following statement is wrong regarding Iron salt?
a) Iron salt produces less floc than Alum
b) Detention time for sedimentation by using Iron salt as coagulant is less
c) Handling of Iron salt requires some skills
d) Iron removes H2S, taste and odor
Explanation: Iron salt produces heavy floc due to which more suspended matter is removed than with alum.
3. __________ is an operation designed to force agitation in the fluid and induce coagulation.
a) Sedimentation
b) Flocculation
c) Disinfection
d) Aeration
Explanation: Flocculation is an agitating process in which destabilized particles are brought into contact to promote agglomeration
4.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
Explanation: 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.
5. What is the dimension formula of mean velocity gradient?
a) 1/T
b) 1/T2
c) T
d) T2
Explanation: Mean velocity gradient is expressed in metre per second/m or Sec-1, so it has dimension formula of 1/T.
6. 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
Explanation: 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.
7. What is the normal value of the detention period adopted in a flocculator for design purpose?
a) 30min
b) 60min
c) 90min
d) 100min
Explanation: The detention period in a flocculator for design purpose should be in the range of 10-40min and its normal value should be 30min
8. 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
Explanation: The normal value of the velocity of flow in a flocculator is 0.4m/s and its range is 0.2-0.8m/s
9. What is the detention period of a clarifier used in the treatment of water?
a) 1hour
b) 2hours
c) 3hours
d) 4hours
Explanation: The detention period of a clarifier is lower than in the plain sedimentation tank and its range is 2.5 to 3 hours
10.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
Explanation: 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.