This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Ammonia Stripping”.
1. Ammonia stripping is done to increase ammonia content.
a) True
b) False
View Answer
Explanation: Ammonia stripping refers to a simple process utilized to lower the ammonia content of a wastewater stream. Some wastewaters contain large amounts of ammonia and/or nitrogen-containing compounds that may readily form ammonia.
2. What is the limit of ammonia content for which ammonia stripping is suited?
a) 10 mg/l
b) 50 mg/l
c) 75 mg/l
d) 100 mg/l
View Answer
Explanation: Ammonia stripping is well suited for wastewater with ammonia levels between 10–100 milligrams per litre (mg/l). Higher ammonia content (more than 100mg/l) may necessitate the use of alternate removal techniques.
3. Above pH 7, ammonia will be in the form of soluble ammonia ions.
a) True
b) False
View Answer
Explanation: All the ammonia will be soluble ammonia ions below pH of 7.5. Above pH 12, ammonia will be present as a dissolved gas. In the range between 7 and 12, both ammonium ions and dissolve gas exist together.
4. What is the state of ammonia above a pH of 12?
a) Dissolved gas
b) Ammonia ions
c) Soluble ions
d) Inert gas
View Answer
Explanation: In the range between 7 and 12, both ammonium ions and dissolve gas exist together. Above pH 12, ammonia will be present as a dissolved gas.
5. Percentage of dissolved gas ________ with temperature and pH.
a) Increases
b) Decreases
c) Does not alter
d) Fluctuates
View Answer
Explanation: In the range between 7 and 12, both ammonium ions and dissolve gas exist together. Various factors favour the removal of ammonium ions where temperature and pressure play a major role.
6. The higher the temperature, the lower the________
a) Ammonia ions
b) Air flow
c) pH
d) Reaction
View Answer
Explanation: At any given temperature and pH, we can determine the amount of air necessary to provide an adequate flow for the ammonia. Generally, the higher the temperature, the lower the air flow.
7. Which of the below factors do not favour high efficiency?
a) High pH
b) Low temperature
c) High air flow
d) Greater packed bed depth
View Answer
Explanation: There are various factors which favour high efficiency and are high pH, high temperature, high air flow and greater packed bed depth.
8. What is the most favourable pH for the operation?
a) 7
b) 8.5
c) 11
d) 13
View Answer
Explanation: While a range of operating conditions is possible, the most common designs are either pH 11 with low temperature water or warming the water to approximately 120°F (with heat recovery) and pH as low as 9.5.
9. Which of the following is an advantage of closed loop?
a) Initial cost
b) Operating cost
c) Disposal of concentrated ammonia sulphate
d) Air emissions
View Answer
Explanation: A closed loop can be used where higher temperatures are preferred to get better efficiency. In the closed loop, the air is sent to an absorber where concentrated ammonium sulphate is formed. The clean air is then recycled back to the stripper.
10. What is the temperature required for thermal destruction?
a) 330˚F
b) 420˚F
c) 550˚F
d) 670˚F
View Answer
Explanation: The air containing ammonia can be treated to meet air pollution control regulations if they will not allow the ammonia to be released. One method to do this is our catalytic oxidation system. The air is sent to the catalytic oxidizer where it is heated up to an operating temperature of approximately 550°F.
11. Which of these equations for an ammonia stripping tower is true.
a) Z = HTU X NTU
b) Z= HTU/NTU
c) Z= NTU/HTU
d) Z= HTU2/NTU
View Answer
Explanation: Z = HTU X NTU, where Z is the height of the ammonia stripping tower. NTU is the number of transfer units. HTU is the height of the transfer units.
12. How is the height of the transfer unit expressed?
a) HTU = L/KlaA
b) HTU = L X KlaA
c) HTU = L2 X KlaA
d) HTU = L2 / KlaA
View Answer
Explanation: HTU = L/KlaA. HTU is the height of transfer units. Kla is the volumetric mass transfer coefficient. A is the cross-sectional area of the tower.
13. What is the liquid loading rate assumed for an ammonia stripping tower for the removal of volatile organic carbon?
a) 400-500 L /m2min
b) 500-600 L /m2min
c) 600-1800 L /m2min
d) 1800-2500 L /m2min
View Answer
Explanation: The liquid loading rate is assumed as 600-1800 L /m2min for an ammonia stripping tower to remove volatile organic carbon. This is also used to remove ammonia. The pH is increased beyond 7 so that ammonia gas is formed and it can be stripped off.
14. What is the liquid loading rate assumed for an ammonia stripping tower for the removal of ammonia?
a) 200-500 L /m2min
b) 40-80 L /m2min
c) 80-200 L /m2min
d) 20-40 L /m2min
View Answer
Explanation: The liquid loading rate is assumed as 40-80 L /m2min for an ammonia stripping tower to ammonia gas. This is also used to remove volatile organic carbon. The pH is increased beyond 7 so that ammonia gas is formed and it can be stripped off.
15. What is the stripping factor assumed for the ammonia stripping tower to remove volatile organic carbon?
a) 1.5-5
b) 5-9
c) 9-13
d) 13-17
View Answer
Explanation: The stripping factor assumed for the ammonia stripping tower to remove volatile organic carbon is 1.5-5. This is unitless. The Volatile organic compounds pose a problem in aerobic and anaerobic digestion.
16. What is the stripping factor assumed for the ammonia stripping tower to remove ammonia?
a) 1.5-5
b) 5-9
c) 9-13
d) 13-15
View Answer
Explanation: The stripping factor assumed for the ammonia stripping tower to remove volatile organic carbon is1.5-5. This is unitless. The ammonia is stripped at alkaline conditions.
17. What is the allowable pressure drop assumed for the ammonia stripping tower to remove ammonia?
a) 800-1200{N/m2}/m
b) 100-400{N/m2}/m
c) 400-800{N/m2}/m
d) 1200-1600{N/m2}/m
View Answer
Explanation: The allowable pressure drop assumed for the ammonia stripping tower to remove ammonia is 100-400{N/m2}/m. It is the same for the removal of volatile organic compounds. Ammonia with a Henry constant 0.75 ATM cannot be stripped.
18. At what pH should be the wastewater be maintained in order to remove the Volatile organic compounds?
a) 5.5-8.5
b) 8.5-11.5
c) 12-15
d) 15-18
View Answer
Explanation: A pH of 5.5-8.5 should be the wastewater be maintained in order to remove the Volatile organic compounds. More alkaline conditions should be maintained. At alkaline conditions, ammonia is formed which can be stripped off easily.
19. What is the packing depth maintained for an ammonia stripping tower for the removal of volatile organic compounds?
a) 1-6 m
b) 6-8 m
c) 8-12 m
d) 12-16 m
View Answer
Explanation: The packing depth is maintained at 1-6 m for an ammonia removal stripping tower for the removal of volatile organic compounds. Height to diameter ratio is maintained at <=10:1. For packing depths greater than 5m redistribution of liquid is recommended.
20. What is the packing depth maintained for an ammonia stripping tower?
a) 2-6 m
b) 6-10 m
c) 10-14 m
d) 14-18 m
View Answer
Explanation: The packing depth is maintained at 2-6 m for an ammonia removal stripping tower for the removal of ammonia compounds. Height to diameter ratio is maintained at <=10:1. For packing depths greater than 5m redistribution of liquid is recommended.
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