Rotary drum filter – principle, construction, working, uses, merits, demerits MCQs With Answer

Rotary drum filter – principle, construction, working, uses, merits, demerits MCQs With Answer

The rotary drum filter is a continuous, vacuum-operated solid-liquid separation device widely used in pharmaceutical processing for filtration, cake washing and solvent recovery. This introduction covers the principle of vacuum-driven filtration, drum construction (perforated shell, filter medium, trough, drive), key operating parameters (speed, immersion depth, vacuum level, cake thickness), and practical applications in API isolation and wastewater treatment. Students will learn merits like continuous operation and easy cake discharge, and demerits such as limited fine-particle retention and solvent loss. Keywords: rotary drum filter, principle, construction, working, cake washing, vacuum filtration, pharmaceutical filtration. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary separation mechanism in a rotary drum filter?

• Gravity settling of solids
• Vacuum-assisted filtration through a filter medium
• Centrifugal force separation
• Electrostatic attraction

Correct Answer: Vacuum-assisted filtration through a filter medium

Q2. Which component forms the rotating surface that supports the filter medium?

• Filter press plate
• Perforated drum shell
• Vacuum manifold
• Scraper blade

Correct Answer: Perforated drum shell

Q3. In a rotary drum filter, the term “immersion depth” refers to:

• The depth of the drum’s perforations
• The portion of the drum submerged in the slurry during rotation
• The thickness of the filter cake after drying
• The distance between drum and vacuum trough

Correct Answer: The portion of the drum submerged in the slurry during rotation

Q4. Which parameter most directly controls cake thickness in a rotary drum filter?

• Drum surface temperature
• Drum rotational speed
• Vacuum pump horsepower
• Ambient humidity

Correct Answer: Drum rotational speed

Q5. Which material is commonly used for filter cloth in pharmaceutical rotary drum filters?

• Cotton only
• Polypropylene or polyester woven cloth
• Galvanized steel mesh
• Paper sheets

Correct Answer: Polypropylene or polyester woven cloth

Q6. What is the role of the vacuum trough in the drum filter?

• Support the drum mechanically
• Collect filtrate and apply vacuum to the drum sectors
• Provide heating to dry the cake
• Store filter cloth rolls

Correct Answer: Collect filtrate and apply vacuum to the drum sectors

Q7. Which of the following is NOT a typical stage in the rotary drum filter cycle?

• Filtration and cake formation
• Cake conditioning with steam sterilization
• Cake washing
• Cake discharge/peel

Correct Answer: Cake conditioning with steam sterilization

Q8. Increasing vacuum level in a rotary drum filter generally results in:

• Lower filtrate flow rate
• Thicker residual filtrate layer
• Higher filtration flux and faster dewatering
• Immediate cake dissolution

Correct Answer: Higher filtration flux and faster dewatering

Q9. What is a common method for discharging cake from the drum surface?

• Manual scraping with a spatula
• Air blowback and mechanical doctor blade or scraper
• Melting the cake with heat
• Centrifuging the cake off the drum

Correct Answer: Air blowback and mechanical doctor blade or scraper

Q10. Which operating factor helps improve washing efficiency of the cake on a rotary drum filter?

• Using higher drum speed during wash
• Applying a lower wash volume
• Increasing wash liquid flow and optimizing spray nozzle distribution
• Reducing vacuum to zero during wash

Correct Answer: Increasing wash liquid flow and optimizing spray nozzle distribution

Q11. One merit of rotary drum filters in pharmaceutical production is:

• They are ideal for sterile aseptic filtration without additional measures
• Continuous operation with relatively low labor requirements
• They can filter nano-colloids without filter aids
• They do not require any maintenance

Correct Answer: Continuous operation with relatively low labor requirements

Q12. A key demerit of rotary drum filters is:

• Inability to handle large volumes
• High capital cost but negligible operating cost
• Poor performance with very fine particles unless filter aids are used
• They cannot be scaled up

Correct Answer: Poor performance with very fine particles unless filter aids are used

Q13. Filter aid like diatomaceous earth is used in drum filters to:

• React chemically with the API
• Improve cake permeability and prevent blinding of filter cloth
• Increase drum rotation speed
• Lower the color of the filtrate

Correct Answer: Improve cake permeability and prevent blinding of filter cloth

Q14. Which design parameter affects both residence time and cake formation on the drum?

• Drum axial length
• Filter cloth color
• Vacuum hose diameter only
• Number of operators present

Correct Answer: Drum axial length

Q15. How does cake compression by a doctor blade influence filtration?

• It reduces cake porosity and improves cake dryness
• It increases porosity and reduces dryness
• It dissolves the cake back into slurry
• It has no effect on cake properties

Correct Answer: It reduces cake porosity and improves cake dryness

Q16. Which is a common material of construction for pharmaceutical-grade drum filters?

• Aluminum with galvanized finish
• 316L stainless steel for wetted parts
• Polyvinyl chloride for drum shell
• Uncoated mild steel throughout

Correct Answer: 316L stainless steel for wetted parts

Q17. In vacuum filtration, what does “flux” refer to?

• The color of the filtrate
• Volume of filtrate per unit area per unit time
• Thickness of the filter cloth
• Rotational speed of drum in rpm

Correct Answer: Volume of filtrate per unit area per unit time

Q18. Which operational change would decrease filtrate clarity due to higher turbidity?

• Using coarser filter cloth mesh
• Adding filter aid
• Reducing drum speed
• Improving wash stages

Correct Answer: Using coarser filter cloth mesh

Q19. What is the purpose of sectoring the drum vacuum into zones?

• To make the drum lighter
• To allow sequential filtration, washing, vacuum drying and cake discharge
• To reduce the number of filter cloths needed
• To increase vacuum pump wear

Correct Answer: To allow sequential filtration, washing, vacuum drying and cake discharge

Q20. Which measurement is most important for sizing the vacuum pump for a rotary drum filter?

• Maximum cake thickness only
• Required vacuum level and expected filtrate flowrate/leakage
• Drum color
• Number of wash nozzles

Correct Answer: Required vacuum level and expected filtrate flowrate/leakage

Q21. What disadvantage does high drum speed present?

• Increased cake thickness
• Reduced volumetric throughput
• Insufficient cake formation and possible poor washing
• Automatic sterilization of cake

Correct Answer: Insufficient cake formation and possible poor washing

Q22. Which test can be used to evaluate the filtration performance of a slurry?

• pH titration only
• Laboratory vacuum filtration or lab-scale rotary drum test to measure flux and cake moisture
• Gas chromatography
• Thin layer chromatography

Correct Answer: Laboratory vacuum filtration or lab-scale rotary drum test to measure flux and cake moisture

Q23. Cake washing aims to:

• Increase cake porosity by dissolving solids
• Replace mother liquor with wash solvent to reduce impurities
• Bind active ingredients irreversibly
• Cool the cake to ambient temperature

Correct Answer: Replace mother liquor with wash solvent to reduce impurities

Q24. Which factor increases the risk of cloth blinding on a drum filter?

• Using coarse particle slurries
• Presence of very fine colloidal particles and lack of filter aid
• Frequent cloth cleaning
• Operating at lower viscosities

Correct Answer: Presence of very fine colloidal particles and lack of filter aid

Q25. What is “wet cake dryness” typically expressed as?

• Dry solids percentage or residual moisture content by weight
• Filtrate color intensity
• Drum rotational speed
• Vacuum pump temperature

Correct Answer: Dry solids percentage or residual moisture content by weight

Q26. For solvent-sensitive APIs, which precaution is essential when using rotary drum filters?

• Using open-air drying only
• Selecting compatible materials and controlling solvent recovery and inert atmosphere if needed
• Heating the drum to high temperatures for rapid drying
• Using reactive filter aids

Correct Answer: Selecting compatible materials and controlling solvent recovery and inert atmosphere if needed

Q27. The cake porosity affects:

• Only the cake color
• Filtrate viscosity exclusively
• Permeability and rate of filtrate flow through the cake
• The drum rotational torque only

Correct Answer: Permeability and rate of filtrate flow through the cake

Q28. How does increasing feed solids concentration usually affect filtration rate?

• It increases filtration rate indefinitely
• It has no effect
• It may reduce filtration rate due to thicker cake formation and higher resistance
• It makes filtrate clearer

Correct Answer: It may reduce filtration rate due to thicker cake formation and higher resistance

Q29. In scale-up of a drum filter process, which approach is commonly used?

• Maintaining geometric similarity but ignoring hydrodynamics
• Using lab data on flux, cake resistance, and adjusting drum area and rotational speed to meet production throughput
• Doubling drum size without testing
• Keeping drum speed constant regardless of area

Correct Answer: Using lab data on flux, cake resistance, and adjusting drum area and rotational speed to meet production throughput

Q30. Which cleaning practice is important for pharmaceutical rotary drum filters?

• Never cleaning the cloth to preserve cake residues
• Regular cloth washing, backwashing or chemical CIP according to validated procedures
• Using only manual dry brushing
• Applying household detergents without validation

Correct Answer: Regular cloth washing, backwashing or chemical CIP according to validated procedures

Q31. What does the specific cake resistance (alpha) indicate?

• Resistance of filter cloth only
• Resistance offered by cake per unit mass to filtrate flow
• Vacuum pump efficiency
• Filter drum horsepower

Correct Answer: Resistance offered by cake per unit mass to filtrate flow

Q32. Which operational strategy reduces airborne solvent emissions during cake discharge?

• Operating at higher drum speed during discharge
• Using containment, inert gas blanket, and solvent recovery measures
• Leaving the cake exposed for longer
• Increasing ambient temperature

Correct Answer: Using containment, inert gas blanket, and solvent recovery measures

Q33. A common sign of filter cloth wear is:

• Increased filtrate turbidity and leakage through cloth
• Lower vacuum pump vibration
• Faster cake drying
• Reduced cake thickness only

Correct Answer: Increased filtrate turbidity and leakage through cloth

Q34. Which cleaning mode uses reverse flow to clear the filter medium?

• Forward washing
• Backwashing or backpulse
• Mechanical scraping only
• Thermal shock cleaning

Correct Answer: Backwashing or backpulse

Q35. The presence of oil or grease in the slurry can cause:

• Improved cake strength always
• Cloth hydrophobic fouling and reduced filtration performance
• No change in filtration
• Instant sterilization

Correct Answer: Cloth hydrophobic fouling and reduced filtration performance

Q36. Which safety concern is important when operating drum filters with flammable solvents?

• Vacuum leaks are irrelevant
• Ignition sources, static charge, and adequate ventilation/ATEX-compliant equipment
• Only biological hazards matter
• Using metal drums prevents any risk

Correct Answer: Ignition sources, static charge, and adequate ventilation/ATEX-compliant equipment

Q37. How can cake cracking or segmentation be beneficial in a drum filter?

• It increases cake hold-up and reduces discharge
• It facilitates cake discharge by creating fracture lines
• It dissolves contaminants
• It always contaminates the filtrate

Correct Answer: It facilitates cake discharge by creating fracture lines

Q38. Which of the following is a typical wash method on a rotary drum filter?

• Top spray wash or immersion wash sequentially
• Sub-zero freezing wash
• High-voltage electric washing
• Direct steam injection into the cake always

Correct Answer: Top spray wash or immersion wash sequentially

Q39. In troubleshooting low filtrate rate, which should be checked first?

• Color of filter cloth
• Vacuum level, cloth condition and slurry viscosity
• Ambient noise levels
• Brand of vacuum pump only

Correct Answer: Vacuum level, cloth condition and slurry viscosity

Q40. Which modification can help separate very fine particles effectively?

• Using a smoother drum surface
• Addition of filter aid or precoat application on the filter cloth
• Decreasing cake thickness to zero
• Removing the vacuum system

Correct Answer: Addition of filter aid or precoat application on the filter cloth

Q41. The term “precoat” refers to:

• Coating drum with paint
• Applying a layer of filter aid on the cloth before filtration to improve retention
• Heating the drum prior to startup
• Spraying disinfectant on the cake

Correct Answer: Applying a layer of filter aid on the cloth before filtration to improve retention

Q42. Which is an economic advantage of rotary drum filters?

• High labor intensity per kg of product
• Capability to process large continuous volumes lowering unit cost
• Extremely low throughput compared to batch filters
• No need for downstream processing

Correct Answer: Capability to process large continuous volumes lowering unit cost

Q43. Why is 316L stainless steel preferred for wetted parts in pharma drum filters?

• Because it is the cheapest metal
• For corrosion resistance, cleanability and regulatory compatibility
• It is magnetic which helps filtration
• It is transparent for observation

Correct Answer: For corrosion resistance, cleanability and regulatory compatibility

Q44. What effect does increasing wash stage count have on impurity removal?

• It always increases cake moisture
• It typically improves impurity removal but increases wash solvent consumption
• It removes the need for filtration
• It reduces cake surface area

Correct Answer: It typically improves impurity removal but increases wash solvent consumption

Q45. Which operational control helps prevent contamination between batches?

• No cleaning between batches
• Validated CIP (clean-in-place) and appropriate changeover procedures
• Changing filter cloth color only
• Using the same wash solvent for all products without validation

Correct Answer: Validated CIP (clean-in-place) and appropriate changeover procedures

Q46. How is filtrate clarity commonly monitored in production?

• By measuring the vacuum only
• Using turbidity meters or offline particle counts
• By cake color assessment visually only
• By weighing the drum

Correct Answer: Using turbidity meters or offline particle counts

Q47. What is the impact of high slurry viscosity on drum filter performance?

• It enhances filtrate flux
• It reduces flow through the cake and slows filtration
• It makes cake lighter
• No impact at all

Correct Answer: It reduces flow through the cake and slows filtration

Q48. Which advantage does a rotary drum filter have over a batch plate filter?

• Better for extremely small-scale lab testing only
• Continuous operation enabling steady production rather than discrete batches
• Inherently sterile without validation
• Zero maintenance requirements

Correct Answer: Continuous operation enabling steady production rather than discrete batches

Q49. What maintenance is crucial for prolonging filter cloth life?

• Exposing cloth to strong acids frequently
• Appropriate chemical cleaning, gentle handling during installation and avoiding abrasive solids
• Never replacing the cloth
• Operating at maximum vacuum always

Correct Answer: Appropriate chemical cleaning, gentle handling during installation and avoiding abrasive solids

Q50. In context of environmental control, how can drum filters reduce waste impact?

• By increasing wash solvent usage indefinitely
• By enabling solvent recovery from filtrate and reducing wastewater solids via efficient dewatering
• By discarding all cake as hazardous waste regardless
• By evaporating filtrate to atmosphere without recovery

Correct Answer: By enabling solvent recovery from filtrate and reducing wastewater solids via efficient dewatering

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com