Environmental Engineering Multiple Choice Questions on “Theory and classification of Filtration”.
1. Which of the following statement is wrong regarding filtration?
a) It removes fine particle
b) It removes suspended solids not removed by sedimentation
c) It does not remove turbidity
d) It removes color
Answer: c
Clarification: Filtration is a primary turbidity removal process. It also removes color, suspended solids and fine particles.
2. In which action of filtration, particles coarser than the void size is arrested?
a) Mechanical Straining
b) Sedimentation
c) Biological mechanism
d) Electrolytic action
Answer: a
Clarification: In Mechanical Straining, particles coarser than the void size is arrested. The water passing the voids will be free from such particles.
3. In which action of filtration, colloidal particles are removed?
a) Mechanical Straining
b) Sedimentation
c) Biological mechanism
d) Electrolytic action
Answer: b
Clarification: In the sedimentation action of filtration, colloidal particles arrested in the voids attract other finer particle, settle down in the voids and get removed.
4. Which is the first zone of purification in a sand bed?
a) Autotrophic zone
b) Heterotrophic zone
c) Schmutzdecke zone
d) Electrolytic zone
Answer: c
Clarification: Schmutzdecke zone is the first zone of purification in a sand bed. It comes under the biological action of filtration. Schmutzdecke is known as the surface coating.
5. Schmutzdecke acts as an extremely fine meshed straining mat.
a) True
b) False
Answer: a
Clarification: Schmutzdecke is a film of algae, bacteria and protozoa formed on the uppermost layer of sand which helps in the breakdown of organic impurities into harmless compounds acting as a fine mesh straining mat.
6. In which action of filtration, removal of particulate matter takes place?
a) Mechanical Straining
b) Sedimentation
c) Biological mechanism
d) Electrolytic action
Answer: d
Clarification: Filter removes the particulate matter by electrostatic exchange where the charge of the filter medium neutralizes the charge of the floc and permitting it to be removed.
7. In which type of filter, rate of filtration is low?
a) Slow sand filter
b) Rapid sand filter
c) Gravity filter
d) Pressure filter
Answer: a
Clarification: In Slow sand filter, rate of filtration is low and due to this they requires large land and are expensive to install.
8. What is the color of the surface coating formed during the filtration process?
a) White
b) Brown
c) Green
d) Reddish brown
Answer: d
Clarification: The surface coating is formed by the reddish brown deposit of partially decomposed organic matter together with Iron, Alumina, Manganese and Silica.
9. In the ________ zone of purification in filter media, bacteria oxidizes the organic matter completely.
a) Autotrophic
b) Heterotrophic
c) Schmutzdecke
d) Electrolytic
Answer: b
Clarification: In Heterotrophic zone, bacteria multiplies in large number, breaks down not only the organic matter but also destroys each other to maintain a balance of life in the filter.
10. The filtration rate of a slow sand filter is _____ litres of water per square metre.
a) 20
b) 30
c) 50
d) 100
Answer: d
Clarification: The surface area of the slow sand filter lies between 50m2 to 1000m2 and its filtration rate lies between 100 to 200 litres of water per m2.
11. Identify the correct statement from the following options.
a) Rapid sand filter has a high initial cost
b) Coagulation is essential in slow sand filter
c) Slow sand filter requires skilled supervision
d) Period of cleaning of Rapid sand filter is 1-2 days
Answer: d
Clarification: Rapid sand filter is cheap and economical and its period of cleaning is 1-2 days. Neither the coagulation nor the skilled supervision is required in the slow sand filter.