This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “UASB Reactor – 1”.
1. UASB is an anaerobic reactor.
a) True
b) False
View Answer
Explanation: The up-flow anaerobic sludge blanket reactor (UASB) is a single tank process in an anaerobic centralized or decentralized industrial wastewater or black water treatment system achieving high removal of organic pollutants.
2. UASB is only used for lower levels of treatment.
a) True
b) False
View Answer
Explanation: The up-flow anaerobic sludge blanket reactors are used in industries for high removal of organic pollutants and achieve high treatment efficiency.
3. How does the wastewater enter the reactor?
a) Bottom
b) Top
c) Side
d) Top and side
View Answer
Explanation: Wastewater enters the reactor from the bottom and flows forward. A suspended sludge blanket filters and treats the wastewater as the wastewater flows through it.
4. A sludge blanket in the reactor is ______
a) At the top
b) At the bottom
c) Absent
d) In between
View Answer
Explanation: Wastewater enters the reactor from the bottom and flows forward. A suspended sludge blanket filters and treats wastewater as the wastewater flows through it.
5. _____ breaks down the organic matter.
a) Bacteria
b) Fungi
c) Virus
d) Algae
View Answer
Explanation: Bacteria living in the sludge blanket breaks down organic matter by anaerobic digestion, transforming it into biogas. Solids are also retained by a filtration effect of the blanket.
6. _________ at the top prevent an outflow of the sludge blanket.
a) Rubber cock
b) Out pipe
c) Baffle
d) Stopper
View Answer
Explanation: The up-flow regime and the motion of the gas bubbles allow mixing without mechanical assistance. Baffles at the top of the reactor allow gases to escape and prevent an outflow of the sludge blanket.
7. What is the size of the microbial granules?
a) 0.3-0.6 mm
b) 0.5-0.8 mm
c) 1-3 mm
d) 3-6 mm
View Answer
Explanation: The sludge blanket is comprised of microbial granules i.e., small agglomeration of micro-organisms that, because of their weight, resist being washed out in the up-flow.
8. What is the product gases released at the end of the UASB process?
a) Methane
b) Methane and carbon-dioxide
c) Oxygen and carbon-dioxide
d) Carbon-dioxide
View Answer
Explanation: The micro-organisms in the sludge layer degrade organic compounds. As a result, gases are released. The rising bubbles mix the sludge without the assistance of any mechanical parts.
9. What is the means used for the mixing of the sludge?
a) Magnetic stirrer
b) Electrically driven stirrer
c) Mechanical mixing
d) By means of bubbles
View Answer
Explanation: The rising bubbles mix the sludge without the assistance of any mechanical parts. Upstream velocity and settling speed of the sludge is in equilibrium and forms a locally rather stable but suspended sludge blanket.
10. _______ deflects the materials downwards.
a) Baffles
b) Sloped walls
c) Deflectors
d) Separator
View Answer
Explanation: Upstream velocity and the settling speed of the sludge is in equilibrium and forms a locally rather stable, but suspended sludge blanket. Sloped walls deflect material that reaches the top of the tank downwards.
11. A clarified effluent is extracted from the ______ of the reactor.
a) Top
b) Side
c) Bottom
d) Central pipe
View Answer
Explanation: The clarified effluent is extracted from the top of the tank in an area above the sloped walls. A gas-liquid-solids separator separates the gas from the treated wastewater and the sludge.
12. What is the minimum pH to be maintained for the process?
a) 5.6
b) 6.3
c) 7.5
d) 8.2
View Answer
Explanation: The pH value needs to be between 6.3 and 7.85 to allow bacteria responsible for anaerobic digestion to grow. The pH value is also important because at high pH- values, ammonia disassociates to NH3 which inhibits the growth of the methane producing bacteria.
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