Wastewater Treatment MCQ – Environmental Engineering

1. In a wastewater treatment process, the biomass produced is 12,000 units, while substrate consumed in 54,000 units. Estimate the biomass synthesis yield.

  1. 0.22
  2. 0.35
  3. 0.45
  4. 0.78
Answer. a

2. At what stage of waste management system can we recycle the waste?

  1. Waste can be recycled during handling and storage only
  2. Waste can be recycled during sorting and processing of waste only
  3. Waste can be recycled during collection and transportation only
  4. Waste can be recycled at any stage
Answer. d

3. Which of the following Anaerobic Reactor does not require any special media to keep sludge in suspension during treatment?

  1. Up flow anaerobic filters
  2. Down flow anaerobic filters
  3. Fluidized bed units
  4. UASB type units
Answer. d

4. Which of the following is an attached growth process used for treating waste water?

  1. Rotating biological contactors
  2. Aerated lagoons
  3. Activated sludge process
  4. Sludge digestion system
Answer. a

5. Winkler’s method is used to determine

  1. Methane content of waste water
  2. Biological Oxygen Demand (BOD) of waste water
  3. Chemical Oxygen Demand (COD) of waste water
  4. Dissolved Oxygen (DO) content of waste water
Answer. d

6. The biochemical treatment of sewage effluents is a process of

  1. Dehydration
  2. Carbonation
  3. Oxidation
  4. Reduction
Answer. c

7. Sewage that has received no purification treatment is called

  1. Raw sewage
  2. Untreated sewage
  3. Crude sewage
  4. Fresh sewage
Answer. c

8. As per IS 2490-1981, the general tolerance limit of biological oxygen demand (5 days at 20°C) in public sewers is

  1. 200 mg/L
  2. 300 mg/L
  3. 350 mg/L
  4. 250 mg/L
Answer. c

9. Minimum concentration of dissolved oxygen that should be ensured while discharging the treated waste water into receiving waters is

  1. 1 ppm
  2. 2 ppm
  3. 3 ppm
  4. 4 ppm
Answer. d

10. What is the main reason for providing an equalization tank in the sewage treatment plant?

  1. Damping the hourly variation in the sewage flow
  2. Damping the daily variations in the sewage flow
  3. Aeration of the sewage
  4. Proper mixing the sewage before further treatment
Answer. a

11. The COD/BOD5 ratio of two wastewater samples from different sources was measured as 1.5 and 3.0 respectively. Based on this information the following conclusion may be arrived at.

  1. The sample with higher COD/BOD5 ratio has more organic matter
  2. The sample with lower COD/BOD5 ratio has higher percentage of biodegradable organic matter
  3. The sample with lower COD/BOD5 ratio is from an industrial source
  4. The sample with higher COD/BOD5 ratio is a sample of domestic sewage
Answer. b

12. Biochemical oxygen demand of wastewater represent

  1. total concentration of biochemical matter
  2. total organic matter
  3. concentration of biodegradable organic matter
  4. concentration of chemically degradable organic matter
Answer. c

13. When wastewater is disposed off into a running stream, 4 zones are formed. In which of the following zones will the minimum level of dissolved oxygen be found?

  1. Zone of degradation
  2. Zone of active decomposition
  3. Zone of recovery
  4. Zone of clear water
Answer. b

14. Consider the following impurities

  1. CO and H2S
  2. Finely divided suspended matter
  3. Disease causing bacteria
  4. Excess alkalinity

The correct sequence of the removal of these impurities in a water treatment plants is

  2. (i) (ii) (iii) (iv)
  3. (iv) (i) (iii) (ii)
Answer. d

15. Which of the following sewage treatment methods has inherent problems of odour, ponding and fly nuisance?

  1. UASB system
  2. Activated sludge process
  3. Trickling filters
  4. Stabilization ponds
Answer. d

16. Sewage treatment units are normally designed for

  1. 15-20 years
  2. 5-10 years
  3. 30-40 years
  4. 40-50 years
Answer. c

17. The BOD removal eificiency in percentage, during primary treatment, under normal conditions is about

  1. 65%
  2. 85%
  3. 30%
  4. zero
Answer. c

18. A treated waste water (initial contaminant concentration, flow rate = 5C, 0.2Q) enters a stream (initial concentration, flow rate =0.01C, Q). Calculate contaminant concentration in stream immediately after mixing of waste water with stream water?

  1. 0.04 C
  2. 0.84 C
  3. 1.2 C
  4. 1.0 C
Answer. b

19. The bio-chemical oxygen demand (BOD) of sewage is measured after

  1. 1 day at 20 °C
  2. 5 day at 25°C
  3. 7 day at 25°C
  4. 5 day at 20°C
Answer. d

20. The coagulant which is generally not used for treating the sewage is

  1. Alum
  2. Ferric Chloride
  3. Ferric sulphate
  4. Chlorinated copperas
Answer. c
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