This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Moving Bed Bioreactor”.
1. MBBR provides support for both autotrophic and heterotrophic bacteria.
a) True
b) False
View Answer
Explanation: Each individual biocarrier increases productivity through providing the protected surface area to support the growth of heterotrophic and autotrophic bacteria within its cells.
2. MBBR needs an assistance to maintain biofilm.
a) True
b) False
View Answer
Explanation: This technology provides cost-effective treatment with minimal maintenance since MBBR processes self-maintain an optimum level of productive biofilm.
3. Which of the following is not correct with respect to MBBR?
a) Compact design
b) Expandable
c) Multiple pass process
d) Load responsive
View Answer
Explanation: MBBR consists of a compact design which is a fraction of the size of conventional systems. It is expandable, single pass process that is there is no requirement of return activated sludge and is load responsive.
4. Which ions are present on the charged surface of MBBR?
a) Iron
b) Iodine
c) Aluminium
d) Sodium
View Answer
Explanation: Charged surfaces on the media are biologically regenerated as ammonium ions which are adsorbed and then subsequently nitrified by the biofilm and desorbed.
5. The ions are desorbed after ______ by the biofilm.
a) Nitrified
b) Denitrified
c) Adsorbed
d) Absorbed
View Answer
Explanation: Charged surfaces on the media are biologically regenerated as ammonium ions which are adsorbed and then subsequently nitrified by the biofilm and desorbed. These reactive surfaces increase treatment efficiency and buffer the biofilm communities against toxic compounds in the wastewater.
6. MBBR was developed based on the activated sludge process and _____
a) Sedimentation process
b) Clarifier process
c) Aeration process
d) Biofilter process
View Answer
Explanation: Charged surfaces on the media are biologically regenerated as ammonium ions which are adsorbed and then subsequently nitrified by the biofilm and desorbed. These reactive surfaces increase treatment efficiency and buffer the biofilm communities against toxic compounds in the wastewater.
7. What part of the tank is used by MBBR for biomass growth?
a) 1/ 4
b) 1/ 2
c) 3/ 4
d) 1/ 1
View Answer
Explanation: The biomass growth is seen in the entire tank. The whole tank is used in MBBR for biomass growth.
8. The biofilm carrier movement is caused by ________
a) Stirring
b) Horizontal shaft
c) Vertical shaft
d) Agitation by air
View Answer
Explanation: The agitation set up by the air in the aerobic process causes biofilm carrier movement, while in anoxic and anaerobic processes a mixer (normally a horizontal shaft mounted banana mixer) keeps the carrier moving.
9. What is the shape of the biofilm carrier?
a) Circular
b) Rectangular
c) Square
d) Cylindrical
View Answer
Explanation: The biofilm carrier is made of high density polyethylene and shaped like a small cylinder with a cross on the inside of the cylinder and “fins” on the outside.
10. What is the length of the cylinder?
a) 2 mm
b) 5 mm
c) 7 mm
d) 10 mm
View Answer
Explanation: The cylinder has a length of 7 mm and a diameter of 10 mm (not including fins). Lately larger carrier of similar shape was introduced, intended for use in plants with coarse inlet sieves.
11. What is the diameter of the cylinder?
a) 5 mm
b) 7.5 mm
c) 10 mm
d) 12 mm
View Answer
Explanation: The cylinder has a diameter of 10 mm (not including fins) and a length of 7 mm. A larger carrier of similar shape was introduced, intended for use in plants with coarse inlet sieves.
12. What is the standard filling degree of MBBR?
a) 50%
b) 55%
c) 67%
d) 72%
View Answer
Explanation: One of the advantages of MBBR is that the filling of a carrier in the reactor may be subjected to preferences. The standard degree of filling of MBBR is 67% resulting in a total specific carrier area of 465m2/m3.
13. What is the retention time considered for aeration tanks in a moving bed bioreactor system?
a) 4hrs
b) 5-6 hrs
c) 6-8 hrs
d) 8-12 hrs
View Answer
Explanation: The retention time considered for an aeration tank for moving bed bioreactor system is 6-8 hrs. In normal cases, without the media the retention time for aeration tank is considered as 8-10 hrs. The media in the moving bed bioreactor increases the surface area and reduces the tank size.
14. What is the surface area of the media used in these moving bed bioreactor systems?
a) 2000 m2
b) 3000 m2
c) 200-300 m2
d) 400-600 m2
View Answer
Explanation: The media increases the surface area of the tank, thus results in a smaller tank size. Generally the media used in these moving bed bioreactors have the surface area in the range 400-600 m2. Recently there have been introductions of new media with a surface area close to 650-700m2.
15. What is the BOD removal level for moving bed bioreactor?
a) 3.5-4.5 Kg BOD/m3day
b) 2-2.75 Kg BOD/ m3day
c) 3 Kg BOD/ m3day
d) 5 Kg BOD/m3day
View Answer
Explanation: The BOD removal for the moving bed bioreactor is 3.5-4.5 Kg BOD/m3day. The Moving bed bioreactor removes nitrogen also. These are provided with diffusers in order to provide aeration.
16. What is the combined BOD and nitrogen removal level for moving bed bioreactor?
a) 3-4 Kg BOD/m3
b) 2-2.75 Kg BOD/m3
c) 5 Kg BOD/m3
d) 6 Kg BOD/m3
View Answer
Explanation: The combined BOD and nitrogen removal for the moving bed bioreactor is 2-2.75 Kg BOD/m3day. The Moving bed bioreactor removes BOD also. These are provided with diffusers in order to provide aeration.
17. Calculate the tank volume for the Moving bed bioreactor system for the following data.
Flow: 500 m3/h.
BOD: 500 mg/L
Retention time: 8 hrs
a) 800 m3
b) 4000 m3
c) 8000 m3
d) 5000 m3
View Answer
Explanation: In this case as the BOD level is high, the retention time considered is 8 hrs. Volume of tank= Flow x Retention time. Volume= 500 X 8= 4000m3.
18. Calculate the tank volume for the Moving bed bioreactor system for the following data.
Flow: 800 m3/h.
BOD: 1500 mg/L
Retention time: 8 hrs
a) 5000 m3
b) 6400 m3
c) 8400 m3
d) 9200 m3
View Answer
Explanation: In this case as the BOD level is high, the retention time considered is 8 hrs. Volume of tank= Flow x Retention time. Volume= 800 X 8= 6400m3.
19. Calculate the tank volume for the Moving bed bioreactor system for the following data.
Flow: 800 m3/h.
BOD: 300 mg/L
Retention time: 6 hrs
a) 4500 m3
b) 4800 m3
c) 6500 m3
d) 10500 m3
View Answer
Explanation: In this case as the BOD level is not that high, hence the retention time considered is 6 hrs. Volume of tank= Flow x Retention time. Volume= 800 X 6= 4800m3.
20. Calculate the tank volume for the Moving bed bioreactor system for the following data.
Flow: 80 m3/h.
BOD: 300 mg/L
Retention time: 6 hrs
a) 500 m3
b) 600 m3
c) 480 m3
d) 120 m3
View Answer
Explanation: In this case as the BOD level is not that high, hence the retention time considered is 6 hrs. Volume of tank= Flow x Retention time. Volume= 8 X 6= 480m3.
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