This set of Advanced Waste Water Engineering Questions and Answers focuses on “Removal of Iron, Manganese and Arsenic – 2”.
1. If the water is brown in colour it indicates the presence of which of these?
a) Iron
b) Manganese
c) Arsenic
d) Barium
View Answer
Explanation: The presence of iron in water is usually indicated by the colour of water. This is usually brown in colour. In some cases, this is usually reddish brown in colour.
2. How is Iron removed?
a) Oxidation
b) Clarifier
c) HRSCC
d) Ultrafiltration
View Answer
Explanation: The Iron is removed by oxidation. The iron is usually present as a ferrous compound. This is usually oxidized to ferric compounds and is precipitated out.
3. What is the safe limit for iron in the water?
a) 0.3 ppm
b) 0.5 ppm
c) 5 ppm
d) 1 ppm
View Answer
Explanation: The safe limit for iron in water is 0.3 ppm. Excessive iron in drinking water can lead to digestive problems. This can cause nausea, vomiting etc.
4. What is the safe limit for manganese in water?
a) 0.05
b) 0.15
c) 0.2
d) 0.25
View Answer
Explanation: The safe limit for manganese in drinking water is 0.05 ppm. According to EPA, manganese concentration is not a concern unless and until it is 10 times the safe limit concentration. Presence of manganese can be found by an impairing colour, odour and taste to the water.
5. What is the method used to delay the precipitation of oxidized manganese and iron?
a) Addition of phosphate
b) Addition of nitrate
c) Addition of hydrogen
d) Addition of chloride
View Answer
Explanation: The method used to delay the precipitation of oxidized manganese and iron is adding phosphate. This is effective when the water contains less than 0.3 ppm of iron. This is also effective when the water contains less than 0.1ppm of manganese.
6. What is the concentration of dissolved oxygen required to oxidize 1 ppm of iron?
a) 0.14 ppm
b) 0.12 ppm
c) 0.15 ppm
d) 0.20 ppm
View Answer
Explanation: 0.14 ppm is required to oxidize 1 ppm of iron. Ferrous compounds are oxidized to ferric compounds. This is then precipitated out.
7. What is the concentration of dissolved oxygen required to oxidize 1 ppm of manganese?
a) 0.2 ppm
b) 0.23 ppm
c) 0.30 ppm
d) 0.27 ppm
View Answer
Explanation: 0.27 ppm is required to oxidize 1 ppm of iron. Manganese can be oxidized by chloride. This can also be oxidized by permanganate.
8. Which of these methods is not used for the removal of arsenic?
a) Activated alumina
b) Green sand
c) Coagulation by Iron hydroxide
d) Activated carbon
View Answer
Explanation: Activated carbon is not used in the removal of arsenic. Activated alumina is one of the methods to remove arsenic. Green sand and coagulation by Iron hydroxide is also one method to remove arsenic.
9. Considering the total cost which of these is the most expensive method to remove arsenic?
a) Green sand
b) Activated alumina
c) Coagulation by Iron hydroxide
d) Tehonoarz method
View Answer
Explanation: The most expensive method to remove arsenic is green sand. The total cost includes capital cost. This total cost also includes operational and maintenance cost and waste disposal cost.
10. Which of these is the most efficient method to remove arsenic?
a) Green sand
b) Tehonoarz
c) Coagulation by Iron hydroxide
d) Activated alumina
View Answer
Explanation: Tehonoarz is the most efficient method to remove arsenic. Activated alumina is the second most efficient method to remove arsenic. Green sand is the least efficient method to remove arsenic.
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