Part 3: Microbes in Sewage Treatment (25 MCQs)
Part 3: Microbes in Sewage Treatment – Primary, Secondary, Tertiary Treatment (25 MCQs)
Q51. Sewage treatment is mainly aimed at:
a) Killing insects
b) Reducing BOD of wastewater
c) Increasing pathogenic load
d) Producing fertilizers only
Answer: b
- b) Correct: Main aim = reduce Biochemical Oxygen Demand (BOD).
Q52. BOD stands for:
a) Biological Oxygen Demand
b) Biochemical Oxygen Demand
c) Biological Organic Decomposition
d) Biochemical Oxidation Device
Answer: b
- b) Correct: BOD = Biochemical Oxygen Demand → oxygen required by microbes to decompose organic matter.
Q53. Higher BOD in water indicates:
a) More pollution and organic matter
b) Pure water
c) Absence of microbes
d) High oxygen availability
Answer: a
- a) Correct: More BOD → more organic pollution.
Q54. Primary treatment of sewage involves:
a) Biological degradation by microbes
b) Removal of large particles by filtration and sedimentation
c) Chemical precipitation
d) UV sterilization
Answer: b
- b) Correct: Primary treatment = physical removal of large particles.
Q55. Secondary treatment is also called:
a) Physical treatment
b) Biological treatment
c) Chemical treatment
d) Sterilization
Answer: b
- b) Correct: Secondary treatment = biological degradation by microbes.
Q56. Which microbes are mainly used in secondary sewage treatment?
a) Viruses
b) Algae and fungi
c) Aerobic bacteria forming flocs
d) Cyanobacteria
Answer: c
- c) Correct: Aerobic bacteria + fungi form flocs → digest organic matter.
Q57. Flocs are:
a) Large inorganic particles
b) Masses of bacteria associated with fungal filaments
c) Viruses in sewage
d) Chemical precipitates
Answer: b
- b) Correct: Flocs = bacteria + fungal filaments in secondary treatment.
Q58. Aeration tanks in sewage treatment plants help in:
a) Anaerobic digestion
b) Providing oxygen for aerobic microbes
c) Killing microbes
d) Chemical treatment
Answer: b
- b) Correct: Aeration tanks supply oxygen → aerobic microbial degradation.
Q59. Activated sludge refers to:
a) Primary sludge
b) Sludge rich in aerobic microbes after secondary treatment
c) Anaerobic sludge
d) Tertiary sludge
Answer: b
- b) Correct: Activated sludge = microbial-rich flocs in aeration tank.
Q60. A part of activated sludge is:
a) Drained to rivers directly
b) Pumped back into aeration tank as inoculum
c) Burned
d) Stored indefinitely
Answer: b
- b) Correct: Some activated sludge is reused as inoculum.
Q61. Remaining activated sludge is:
a) Discharged untreated
b) Digested anaerobically in sludge digesters
c) Frozen
d) Mixed with drinking water
Answer: b
- b) Correct: Anaerobic digesters degrade organic matter → release biogas.
Q62. Anaerobic sludge digestion produces:
a) Only CO₂
b) Biogas (CH₄, CO₂, H₂S)
c) Pure O₂
d) Nitrogen gas only
Answer: b
- b) Correct: Biogas mixture → methane, CO₂, H₂S.
Q63. Methanogens in sludge digesters include:
a) Methanobacterium
b) Lactobacillus
c) Rhizobium
d) Aspergillus
Answer: a
- a) Correct: Methanobacterium = methanogen in biogas/anaerobic digesters.
Q64. The measure of sewage pollution is:
a) COD only
b) BOD value
c) Oxygen saturation
d) pH value
Answer: b
- b) Correct: BOD is direct indicator of organic pollution.
Q65. Tertiary treatment of sewage involves:
a) Physical separation
b) Strong chemical/UV treatment to remove pathogens
c) Only sedimentation
d) Addition of antibiotics
Answer: b
- b) Correct: Tertiary treatment = chemical disinfection (chlorination/UV).
Q66. Primary sludge mainly contains:
a) Inorganic salts
b) Sand, silt, large solids, and organic matter
c) Bacteria only
d) Algae
Answer: b
- b) Correct: Primary sludge = large particles + organic matter.
Q67. Secondary effluent after treatment is:
a) Pure drinking water
b) Released into natural water bodies
c) Recycled directly as domestic water
d) Sterile water
Answer: b
- b) Correct: Treated water → discharged into rivers/lakes.
Q68. Which stage of sewage treatment reduces pathogenic load?
a) Primary
b) Secondary
c) Tertiary
d) Digestion
Answer: c
- c) Correct: Tertiary treatment kills remaining pathogens.
Q69. The most important role of microbes in sewage treatment is:
a) Breaking down inorganic salts
b) Degrading organic pollutants
c) Killing protozoa
d) Removing oxygen
Answer: b
- b) Correct: Microbes decompose organic waste → reduce BOD.
Q70. Septic tanks in rural areas are equivalent to:
a) Primary sewage treatment
b) Secondary sewage treatment
c) Tertiary sewage treatment
d) Industrial treatment
Answer: b
- b) Correct: Septic tanks = anaerobic microbial treatment (secondary level).
Q71. Which by-product of sewage treatment is useful as fertilizer?
a) Methane
b) Activated sludge (digested)
c) Sulphur dioxide
d) Ozone
Answer: b
- b) Correct: Digested sludge = manure/fertilizer.
Q72. “Flocs” in sewage treatment contain mainly:
a) Viruses
b) Fungi + aerobic bacteria
c) Algae only
d) Protozoa only
Answer: b
- b) Correct: Flocs = aerobic bacteria + fungal filaments.
Q73. Why must sewage be treated before release into rivers?
a) To remove salts
b) To reduce BOD and pathogens
c) To increase oxygen
d) To make it drinkable
Answer: b
- b) Correct: Untreated sewage → high BOD, pathogens → water pollution.
Q74. Which gas in biogas mixture is combustible?
a) CO₂
b) H₂S
c) CH₄ (methane)
d) N₂
Answer: c
- c) Correct: Methane = main combustible fuel in biogas.
Q75. Which of the following is correct regarding sewage treatment?
a) Primary treatment uses microbes
b) Secondary treatment uses microbes to oxidize organic matter
c) Tertiary treatment increases BOD
d) Activated sludge contains no microbes
Answer: b
- b) Correct: Secondary treatment = microbial degradation (reduces BOD).
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