Environmental Engineering Interview Questions for freshers on “Removal of Iron, Manganese, Colour, Odour and Taste”.
1. Iron and Manganese are generally present in water supplies as ____________
a) Suspension
b) Solution
c) Colloidal particles
d) Either suspension or solution
Answer: d
Clarification: Iron and Manganese are generally present in water supplies in the form of hydrated oxide as suspension and bicarbonates as a solution.
2. What concentration of iron and manganese will cause unpleasant taste and odor of water?
a) 1ppm
b) 2ppm
c) 3ppm
d) >3ppm
Answer: d
Clarification: When the concentration of iron and manganese is greater than 3, it will result in unpleasant taste and odor, unwanted precipitation and difficulties in manufacturing processes.
3. The presence of Sulfate iron in the water results in ____________
a) Odorless water
b) Acidity in water
c) Colorless water
d) Growth of crenothrix in water mains
Answer: b
Clarification: The presence of Sulfate iron in the water results in acidity in water and corrosiveness on iron and brass.
4. The reddish tinge in the water is due to the presence of ____________
a) Zinc
b) Copper
c) Iron
d) Manganese
Answer: c
Clarification: The reddish tinge in the water is due to the presence of iron. Water contains iron by the reaction of CO2 in contact with iron ore forming soluble ferrous bicarbonate.
5. The brown tinge in the water is due to the presence of ____________
a) Zinc
b) Copper
c) Iron
d) Manganese
Answer: d
Clarification: The brown tinge in the water is due to the presence of manganese, which occurs when it is present in an amount greater than 0.3ppm.
6. By aeration process, dissolved iron is oxidized into ____________
a) Ferrous oxide
b) Ferric oxide
c) Ferrous hydroxide
d) Ferric hydroxide
Answer: b
Clarification: By aeration process, dissolved iron is oxidized into ferric oxide, which is insoluble in water.
7. By which process dissolved manganese compounds can be converted into insoluble manganese compounds?
a) Aeration
b) Coagulation
c) Sedimentation
d) Flocculation
Answer: a
Clarification: The dissolved manganese compounds can be converted into insoluble manganese compounds by aeration The precipitated floc can be settled down in settling tanks.
8. For removal of iron from water ________ mg of oxygen is required.
a) 0.14
b) 0.50
c) 1
d) 1.5
Answer: a
Clarification: The reaction for removal of iron from water is – 4Fe + O2 + 10H2O = 4Fe (OH)3 + 8H
1mg of Fe requires 0.14 mg of O2.
9. For removal of manganese from water ________ mg of oxygen is required.
a) 0.14
b) 0.50
c) 0.29
d) 0.90
Answer: c
Clarification: The reaction for removal of manganese from water is – 4Mn + 3O2 + 6H2O = 6MnO2 + 12H
1mg of Mn requires 0.29 mg of O2.
10. Removal of manganese from water takes place at a pH of ______
a) 1.5
b) 3
c) 6
d) 9.4
Answer: d
Clarification: Removal of manganese from water takes place at a pH between 9.4 to 9.6. Pre- chlorination up to 0.7 to 1 mg/l affect the oxidation and precipitation of manganese.
11. When small amounts of iron and manganese are present in water, they are removed by ____________
a) Aeration
b) Coagulation
c) Manganese zeolite
d) Filtration
Answer: c
Clarification: When small amounts of iron and manganese are present in water, they are removed by manganese zeolite where iron and manganese are oxidized to insoluble hydrated oxides which are removed by filtration action of zeolite bed.
12. Removal of iron from water takes place at a pH of ______
a) 1.5
b) 3
c) 8.2
d) 9.4
Answer: d
Clarification: Removal of iron from water takes place at a pH of 8.2. It can be removed in an oxidized condition by softening water by the excess lime process.
13. The taste produced by a microorganism, can be controlled by ____________
a) Potassium per-manganate
b) Potassium dichromate
c) Sodium chloride
d) Iodine
Answer: a
Clarification: The taste produced by a microorganism, can be controlled by potassium per-manganate. It can be controlled alone or in combination with chlorine.
14. Which of the following regarding ozonation is incorrect?
a) Improves the appearance of water
b) Removes traces of color
c) Remove odor
d) Remove phenolic and algae taste
Answer: d
Clarification: Ozonation improves the appearance of water, removes traces of color, remove odor and is also effective against earthy and moldy tastes and odor.
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