Activated sludge and trickling filter process MCQs Civil

1. The activated sludge process is primarily used for:
(A) Primary sedimentation
(B) Secondary treatment of wastewater
(C) Tertiary nutrient removal
(D) Screening of solids

2. In an activated sludge system, microorganisms grow in:
(A) Suspended form in aeration tank
(B) Attached form on filter media
(C) Settled sludge only
(D) Trickling filter only

3. The purpose of the aeration tank in activated sludge is to:
(A) Remove grit
(B) Remove nitrogen only
(C) Supply oxygen for microbial oxidation of organics
(D) Settle sludge

4. Secondary clarifier in activated sludge system is used for:
(A) Aeration
(B) Grit removal
(C) Disinfection
(D) Sludge settling and separation

5. Trickling filter process involves:
(A) Suspended microbial growth
(B) Attached microbial growth on media
(C) Sedimentation only
(D) Chemical oxidation

6. The main difference between trickling filter and activated sludge is:
(A) Type of microbial growth
(B) Type of influent
(C) Type of effluent only
(D) Size of the plant only

7. Return activated sludge (RAS) in activated sludge system is:
(A) Fresh wastewater
(B) Effluent after disinfection
(C) Settled microorganisms returned to aeration tank
(D) Trickling filter media

8. Hydraulic retention time (HRT) in aeration tanks is usually:
(A) Few minutes
(B) Only 2–3 minutes
(C) Several weeks
(D) Few hours to 1 day

9. The organic matter removal in activated sludge is measured by:
(A) Total solids
(B) Biochemical oxygen demand (BOD)
(C) pH only
(D) Temperature

10. Trickling filters are commonly made of:
(A) Porous rock, plastic media, or slag
(B) Sand beds
(C) Concrete only
(D) Steel

11. Sloughing in trickling filter refers to:
(A) Settling of solids in clarifier
(B) Detachment of microbial biomass from media
(C) Aeration process
(D) Screening of influent

12. The main advantage of activated sludge over trickling filter is:
(A) Lower energy requirement
(B) Lower maintenance
(C) Better control over microbial population
(D) Simpler construction

13. In trickling filters, the airflow is primarily for:
(A) Cooling the media
(B) Settling solids
(C) Removing grit
(D) Supplying oxygen to microbes

14. Sludge age or mean cell residence time (MCRT) is an important parameter for:
(A) Activated sludge process
(B) Trickling filter only
(C) Primary screening
(D) Aerated lagoons only

15. Organic loading rate in trickling filter is expressed in:
(A) m³/day
(B) mg/L only
(C) kg BOD/m³/day
(D) Percent solids

16. Diffused aeration in activated sludge:
(A) Removes solids
(B) Provides uniform oxygen supply
(C) Removes pathogens
(D) Settles sludge

17. Trickling filter effluent is usually:
(A) Low in BOD but high in suspended solids
(B) High in BOD
(C) Completely free of nutrients
(D) Only clear water

18. Activated sludge process can remove:
(A) Only solids
(B) BOD, suspended solids, and partially nutrients
(C) Only nitrogen
(D) Only phosphorus

19. Recirculation ratio in trickling filter system is:
(A) Ratio of RAS to influent
(B) Ratio of aeration tank volume to sludge volume
(C) Ratio of primary sludge to influent
(D) Ratio of recycled effluent to influent

20. The key disadvantage of trickling filters is:
(A) High energy requirement
(B) Larger land area required
(C) Excessive aeration needed
(D) Complex operation

21. In activated sludge, sludge volume index (SVI) is used to:
(A) Determine influent flow
(B) Determine BOD only
(C) Measure settleability of sludge
(D) Measure effluent pH

22. Trickling filter media provides:
(A) Surface area for microbial growth
(B) Flow measurement
(C) Grit removal
(D) Disinfection

23. Filamentous bulking in activated sludge leads to:
(A) Excellent settling
(B) Poor sludge settling and high SVI
(C) Increased BOD removal
(D) Lower aeration demand

24. Trickling filter is classified as:
(A) Suspended growth system
(B) Disinfection system
(C) Primary sedimentation unit
(D) Attached growth system

25. Oxygen requirement in activated sludge process is determined by:
(A) Influent BOD and temperature
(B) Media type only
(C) Clarifier depth only
(D) Trickling filter recirculation

26. Trickling filter effluent may require:
(A) No further treatment
(B) Secondary sedimentation to remove sloughed solids
(C) Only screening
(D) Only grit removal

27. Extended aeration is a modification of:
(A) Trickling filter
(B) Primary sedimentation
(C) Activated sludge process
(D) Screening

28. Sludge from trickling filter is typically:
(A) Thick and easy to settle
(B) Low in solids, requiring secondary settling
(C) High in nutrients
(D) Only liquid effluent

29. Nitrification in activated sludge requires:
(A) Anaerobic conditions
(B) Chemical addition only
(C) Trickling filter only
(D) Aerobic conditions

30. The main operational control parameter in activated sludge is:
(A) pH only
(B) Dissolved oxygen concentration and sludge age
(C) Flow measurement only
(D) Media depth