# Waste Water Engineering Questions and Answers – Removal of Iron, Manganese and Arsenic – 1

This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Removal of Iron, Manganese and Arsenic – 1”.

1. In which year was the Ferrosand process patented?
a) 1960
b) 1965
c) 1970
d) 1975

Explanation: The manganese greensand process has been used in the United States since the 1950s. During the early years of its use, Hungerford & Terry, Inc. of Clayton, New Jersey, worked to improve the process and eventually developed the Ferrosand® CR Process, patented in 1965.

2. What is the permitted concentration of manganese in drinking water?
a) 30 g/l
b) 40 g/l
c) 50 g/l
d) 60 g/l

Explanation: The permitted concentration of manganese in drinking water is 50g/l. The manganese greensand process has been used in the United States since the 1950s.

3. What is the permitted concentration of iron in drinking water?
a) 100 g/l
b) 200 g/l
c) 300 g/l
d) 400 g/l

Explanation: The permitted concentration of iron in drinking water is 200g/l. The permitted concentration of manganese in drinking water is 50g/l. The permitted concentration of arsenic in drinking water is 10g/l.

4. What is the permitted concentration of arsenic in drinking water?
a) 10 g/l
b) 20 g/l
c) 30 g/l
d) 40 g/l

Explanation: The permitted concentration of arsenic in drinking water is 10g/l. The permitted concentration of iron in drinking water is 200g/l. The permitted concentration of manganese in drinking water is 50g/l.

5. What is the minimum time of aeration?
a) 20 minutes
b) 40 minutes
c) 60 minutes
d) 80 minutes

Explanation: The water is aerated for a period of no less than 60 minutes. If water flow is 50 m3/h the aeration level is 100m3/h of air and tank volume is 50m3 of water.

6. What is the tank volume of aeration for water flow of 50m3/h?
a) 40 m3
b) 50 m3
c) 80 m3
d) 100 m3

Explanation: The water is aerated for a period of no less than 60 minutes. The tank volume of aeration for water flow of 50m3/h is 50 m3.

7. At what pH should the water be maintained?
a) 6.5
b) 7.5
c) 8.5
d) 9

Explanation: The pH of the water should be increased to a value over pH 7.5. The decrease in the value of pH leads to increase in the acidity of water.

8. The aeration system will decrease the redox potential of the water.
a) True
b) False

Explanation: The aeration system will increase the redox potential of the water. It is important to raise the potential to as high a value as possible. Certainly, it should be over 200mv.

9. What is the minimum required redox potential of water?
a) 100 mv
b) 200 mv
c) 300 mv
d) 400 mv

Explanation: The minimum required redox potential of water is 200 mv. Manganese oxidation requires a high oxidation potential.

10. Manganese oxidation requires a high oxidation potential.
a) True
b) False

Explanation: Manganese oxidation requires a high oxidation potential, in some cases if there is a high BOD or organic content in the water it may be required to add additional oxidizing agents such as hypochlorite, chlorine dioxide, hydrogen peroxide or ozone.

11. What is the desirable bed depth for AFM filtration?
a) 1000 mm
b) 1200 mm
c) 1500 mm
d) 1800 mm

Explanation: The desirable bed depth of AFM filtration is 1200 mm. Maximum bed depth can be within 3000 mm and the bulk density is 1.25-1.

12. What is the maximum allowable flow for backwash?
a) 20 m/hr
b) 45 m/hr
c) 60 m/hr
d) 80 m/hr

Explanation: The maximum allowable water flow for backwash is 60 m/hr. The recommended water flow for backwash is 45 m/hr.

Sanfoundry Global Education & Learning Series – Waste Water Engineering.

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