Sludge treatment and disposal MCQs Civil

1. Sludge is mainly produced in:
(A) Screening units
(B) Primary and secondary sedimentation tanks
(C) Grit chambers
(D) Aeration tanks only

2. The main purpose of sludge thickening is to:
(A) Reduce water content and volume
(B) Remove pathogens
(C) Increase flow rate
(D) Increase BOD

3. Gravity thickening is based on:
(A) Chemical reaction
(B) Centrifugal force
(C) Filtration
(D) Settling of solids under gravity

4. Sludge digestion is primarily used for:
(A) BOD removal
(B) Sedimentation
(C) Stabilization of organic matter
(D) Aeration

5. Anaerobic digestion of sludge produces:
(A) Oxygen
(B) Methane and carbon dioxide
(C) Nitrogen only
(D) Sulfuric acid

6. Aerobic digestion requires:
(A) Coagulation chemicals
(B) No oxygen
(C) High temperature only
(D) Oxygen supply

7. Sludge dewatering aims to:
(A) Reduce solids
(B) Increase water content
(C) Remove organic matter only
(D) Increase sludge volume

8. Common methods for sludge dewatering include:
(A) Grit removal
(B) Screening only
(C) Filtration, centrifugation, belt presses
(D) Aeration tanks

9. Lime stabilization of sludge:
(A) Reduces odor and pathogens
(B) Increases BOD
(C) Reduces flow rate only
(D) Removes grit

10. Sludge drying beds work by:
(A) Chemical precipitation
(B) Filtration through sand
(C) Aeration only
(D) Evaporation and percolation

11. Centrifugal dewatering separates sludge by:
(A) Centrifugal force
(B) Gravity
(C) Filtration
(D) Chemical reaction

12. Anaerobic digesters are usually operated at:
(A) Low temperature (<10°C)
(B) Mesophilic (30–38°C) or thermophilic (50–60°C) range
(C) Room temperature only
(D) Below freezing

13. Stabilized sludge is safer for:
(A) Direct discharge to river
(B) Aeration tanks only
(C) Land application
(D) Screening units

14. The term “biosolids” refers to:
(A) Untreated raw sludge
(B) Treated and stabilized sludge suitable for reuse
(C) Sludge only in digesters
(D) Grit removed from wastewater

15. Thermal drying of sludge is used to:
(A) Reduce moisture content to <10%
(B) Increase volume
(C) Remove grit
(D) Increase BOD

16. Sludge incineration is mainly for:
(A) Screening
(B) Aeration
(C) Sedimentation
(D) Volume reduction and destruction of pathogens

17. Dewatered sludge is often stored in:
(A) Sludge lagoons
(B) Grit chambers
(C) Aeration tanks
(D) Trickling filters

18. Thickened sludge has a typical solids content of:
(A) 0.5–1%
(B) 3–8%
(C) 20–30%
(D) 50%

19. Sludge holding tanks are used to:
(A) Aerate water
(B) Remove grit only
(C) Equalize flow and allow initial digestion
(D) Screen solids

20. Alkaline stabilization of sludge is done using:
(A) Chlorine
(B) Lime
(C) Sodium hydroxide only
(D) Hydrogen peroxide

21. Mechanical dewatering is preferred over drying beds when:
(A) Land is scarce
(B) Water is available
(C) BOD is high
(D) Odor is low

22. The retention time in anaerobic digesters is typically:
(A) 1–2 hours
(B) 1–2 minutes
(C) 1 year
(D) 15–30 days

23. Pathogen reduction in sludge can be achieved by:
(A) Settling only
(B) Aerobic or anaerobic digestion, lime treatment, or heat
(C) Screening
(D) Chemical precipitation only

24. Thickened sludge is usually pumped to:
(A) Digesters or dewatering units
(B) Screening units
(C) Grit chambers
(D) Aeration tanks

25. Landfilling of sludge requires:
(A) Only dewatering
(B) Direct disposal without treatment
(C) Stabilization to reduce odor and pathogens
(D) Aeration

26. Sludge from chemical treatment processes may require:
(A) Special handling due to toxicity
(B) Only aeration
(C) Screening
(D) Only sedimentation

27. Dewatering using belt filter presses involves:
(A) Gravity only
(B) Mechanical pressure
(C) Centrifugal force
(D) Evaporation

28. Sludge lagoons are designed for:
(A) Temporary storage and partial digestion
(B) Aeration only
(C) Screening
(D) Trickling filtration

29. Digesters reduce sludge volume primarily by:
(A) Water evaporation
(B) Conversion of organic matter to gases
(C) Filtration
(D) Screening

30. The main environmental concern in sludge disposal is:
(A) Pathogens, odor, and leachate pollution
(B) Only BOD
(C) Only solids content
(D) Only color