This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Nitrogen Removal”.
1. What is the oxidation state of organic nitrogen?
a) -2
b) -1
c) -3
d) +3
View Answer
Explanation: The oxidation state of organic nitrogen is – 3, Ammonia is – 3, Ammonium ion is – 3, gas Nitrogen gas is 0, Nitrous oxide is +1, Nitric oxide is +2, Nitrite ion is +3 and Nitrogen dioxide is +4.
2. Which of the following below represents nitrate ion?
a) NO2
b) NO3–
c) NO–
d) NO2–
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Explanation: Organic nitrogen is represented by N, ammonia is represented by NH3, nitrate ion is represented by NO3– and nitrite ion is represented by NO2–. The oxidation state of nitrate ion is +5.
3. Nitrogen fixation is the conversion of _________into nitrogen compounds.
a) Ammonia
b) Nitric oxide
c) Nitrate
d) Nitrogen gas
View Answer
Explanation: Nitrogen fixation is the conversion of nitrogen gas into nitrogen compounds that can be assimilated by plants. Biological fixation is the most common, but fixation can also occur by lightning and through an industrial process.
4. ______ is the biochemical degradation of Organic-N into NH3 or NH4+.
a) Nitrogen fixation
b) Ammonification
c) Nitrification
d) Denitrification
View Answer
Explanation: Ammonification is the biochemical degradation of Organic-N into NH3 or NH4+ by heterotrophic bacteria under aerobic or anaerobic conditions.
5. Which of the following bacteria is used in nitrification process?
a) Escherichia coli
b) Nitrosomonas
c) Morganella
d) Providencia
View Answer
Explanation: Nitrification is the biological oxidation of NH4+ to NO3– through a two-step autotrophic process by the bacteria Nitrosomonas and Nitrobacter.
6. What is the minimum mass loading of nitrogen in domestic wastewater?
a) 2 lbs
b) 4 lbs
c) 6 lbs
d) 8 lbs
View Answer
Explanation: The mass loading of nitrogen in domestic wastewater averages from 4 to 18 lbs of Total -N per capita per year. Untreated domestic wastewater typically contains 20 to 85 mg/L Total –N.
7. What is the minimum quantity of nitrogen present in untreated wastewater?
a) 5 mg/L
b) 10 mg/L
c) 15 mg/L
d) 20 mg/L
View Answer
Explanation: Untreated domestic wastewater typically contains 20 to 85 mg/L Total -N, with the majority occurring as a mixture of NH3 – N/NH4 + – N (12 -50 mg/L) and Organic -N (8 -35 mg/L).
8. Excess nitrogen is present after secondary biological treatment.
a) True
b) False
View Answer
Explanation: Because the carbon to nitrogen ratio of wastewater is typically on the order of 4:1 to 6:1, there will be excess nitrogen after secondary biological treatment that cannot be assimilated by micro-organisms.
9. The maximum removal of nitrogen from septic tanks is 15%.
a) True
b) False
View Answer
Explanation: The removal of Total -N within septic tanks is on the order of 10 to 30%, with the majority being removed as particulate matter through sedimentation or flotation process.
10. What is the percentage of nitrogen removal that can be obtained from facultative lagoons?
a) 50%
b) 65%
c) 85%
d) 95%
View Answer
Explanation: The pH fluctuates as a result of the algae carbonate interactions in the lagoon, so wastewater alkalinity is important. Under ideal 4 conditions, up to 95% nitrogen removal can be achieved from facultative wastewater stabilization lagoons.
11. What is the power consumed for the anoxic process for the removal of nitrogen?
a) 0.5-1.5 hrs
b) 1.5-2 hrs
c) 2-4 hrs
d) 4-8 hrs
View Answer
Explanation: The retention time considered for the aerobic zone for the AO process for removing phosphorus is 0.5-1.5 hrs. This process involves aerobic oxidation followed by anaerobic digestion. This is a very effective method to remove phosphorus compounds.
12. What is the retention time considered for the anaerobic zone for the AO process for removing phosphorus?
a) 1-3 hrs
b) 3-5 hrs
c) 5-8 hrs
d) 8-11 hrs
View Answer
Explanation: The retention time considered for the anaerobic zone for the AO process for removing phosphorus is 1-3 hrs. This process involves aerobic oxidation followed by anaerobic digestion. This is a very effective method to remove phosphorus compounds.
13. What is the SDNR assumed while designing postanoxic tank?
a) 0.1-0.4
b) 1.5-2
c) 0.8-1
d) 3-4
View Answer
Explanation: The SDNR assumed while designing postanoxic tank is 0.1-0.4. Denitrifying bacteria exist in order to remove nitrogen biologically. The value for SDNR is different for a preanoxic tank.
14. How is the SDNR related to the BOD?
a) SDNR = 0.03 F/M
b) SDNR = 0.3 F/M
c) SDNR = 0.03/( F/M)
d) SDNR = 3 F/M
View Answer
Explanation: SDNR = 0.03 F/M. This is how SDNR is related to F/M. BOD actually represents the F/M.
15. At what detention time maximum saturation rates are experienced in a denitrification process?
a) 10-20 mins
b) 72 mins
c) 30-40 mins
d) 22-24 mins
View Answer
Explanation: When the detention time is 10-20 mins saturation rates are expected in a denitrification process. In this case, the F/M ratio will be very high. The rbCOD also would be very high.
16. When is internal recirculation required for preanoxic tank?
a) SDNR<1
b) SDNR=1
c) SDNR =2-4
d) SDNR =4-6
View Answer
Explanation: The internal recirculation is not required if SDNR<1. Any value of SDNR>1 requires internal recirculation. Internal recirculation value is usually between 2-4.
17. What is the retention time considered for an anoxic zone for the removal of nitrogen for modified Ludzack Ettinger treatment system?
a) 1-3 hrs
b) 3-4 hrs
c) 4-8 hrs
d) 8-12 hrs
View Answer
Explanation: The retention time considered for an anoxic zone for the modified Ludzack Ettinger system is 1-3 hrs. This treatment is used to remove nitrogen. This also aids in removing BOD.
18. What is the residential time considered for the sequence batch reactor for the removal of nitrogen?
a) 42-45 days
b) 10-32 days
c) 32-52 days
d) 52-72 days
View Answer
Explanation: The residential time considered for the sequence batch reactor for the removal of nitrogen is 10-32 days. This SBR is the process which consumes very less space. The whole process takes place in a single tank.
19. While designing SBR for the removal of nitrogen what is the MLVSS in mg/L assumed?
a) 3000-500
b) 7000-9000
c) 9000-10000
d) 60000
View Answer
Explanation: While designing SBR for the removal of nitrogen what is the MLVSs assumed is 2000-5000 mg/L. Based on this the tank size is derived. The total retention time considered for the removal of nitrogen by SBR is 20-30 hrs.
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