Water Treatment – WFI Systems MCQs With Answer

Introduction: Water Treatment – WFI Systems MCQs With Answer is designed for M.Pharm students preparing for MIP 203T – Pharmaceutical Production Technology. This set of questions focuses on Water for Injection (WFI) systems, covering production methods, quality attributes, microbial control, system design, monitoring parameters, validation and regulatory considerations. The MCQs emphasize practical understanding and deeper technical aspects such as distillation principles, membrane alternatives, TOC, endotoxin control, storage/recirculation, sanitization strategies, sampling points and routine testing. These questions will help students develop critical knowledge required for manufacturing sterile products and for exam preparation, quality assurance and process validation discussions.

Q1. What is the primary quality requirement that distinguishes Water for Injection (WFI) from Purified Water?

• Lower conductivity only
• Absence of endotoxins and pyrogens up to pharmacopeial limits
• Higher dissolved oxygen content
• Presence of residual disinfectant

Correct Answer: Absence of endotoxins and pyrogens up to pharmacopeial limits

Q2. Which production method has traditionally been considered the gold standard for producing WFI?

• Reverse osmosis followed by ultrafiltration
• Multi-stage flash evaporation
• Pure distillation (multiple-effect or single-effect)
• Ion exchange only

Correct Answer: Pure distillation (multiple-effect or single-effect)

Q3. Which parameter is most relevant for monitoring organic contamination in WFI systems?

• pH
• Total Organic Carbon (TOC)
• Turbidity
• Chloride concentration

Correct Answer: Total Organic Carbon (TOC)

Q4. For microbial control in a WFI recirculation loop, which of the following is a commonly employed preventative measure?

• Intermittent aeration of storage tanks
• Maintaining continuous recirculation and heating
• Adding low levels of chlorine to the loop
• Stopping circulation during off-hours to conserve energy

Correct Answer: Maintaining continuous recirculation and heating

Q5. Which type of filter is typically used at a final point-of-use to ensure sterility of WFI to a product contact point?

• 5 µm polypropylene prefilter
• 0.45 µm sediment filter
• 0.2 µm sterilizing-grade membrane filter
• Activated carbon filter

Correct Answer: 0.2 µm sterilizing-grade membrane filter

Q6. What does a sudden increase in TOC in a WFI distribution system most likely indicate?

• An increase in system pressure
• Organic contamination or biofilm detachment
• A drop in water temperature only
• An improvement in conductivity

Correct Answer: Organic contamination or biofilm detachment

Q7. Which regular test is essential for monitoring endotoxin levels in WFI used for parenteral manufacturing?

• Bacterial endotoxin test (BET) using LAL or recombinant alternatives
• Gram staining of WFI samples
• pH titration test
• Sulfate content assay

Correct Answer: Bacterial endotoxin test (BET) using LAL or recombinant alternatives

Q8. What is the most effective sanitization method for a stainless-steel WFI loop to control microbial contamination without leaving residues?

• Continuous dosing of sodium hypochlorite
• Thermal (hot water/steam) sanitization at validated temperature and time
• Daily flushing with purified water only
• Periodic acid treatment without rinsing

Correct Answer: Thermal (hot water/steam) sanitization at validated temperature and time

Q9. Which unit operation is commonly used upstream of a WFI distillation plant to protect the distillation train?

• Ion exchange alone
• Reverse osmosis followed by dechlorination and softening
• Ultrafiltration as the sole pretreatment
• Activated carbon only

Correct Answer: Reverse osmosis followed by dechlorination and softening

Q10. In system design, why is eliminating deadlegs in WFI piping critical?

• To reduce heat loss from the system
• To minimize areas of stagnation that promote microbial growth and biofilm formation
• To save on initial piping material costs
• To allow easier installation of sensors

Correct Answer: To minimize areas of stagnation that promote microbial growth and biofilm formation

Q11. Which parameter provides the best immediate indication of ionic purity of WFI?

• Turbidity (NTU)
• Conductivity or resistivity
• Total plate count
• UV absorbance at 254 nm

Correct Answer: Conductivity or resistivity

Q12. What is the primary reason for installing HEPA vents on WFI storage tanks?

• To de-aerate the water and remove dissolved gases
• To filter incoming air and prevent particulate and microbial contamination during tank breathing
• To cool the water in the storage tank
• To reduce tank pressure to vacuum levels

Correct Answer: To filter incoming air and prevent particulate and microbial contamination during tank breathing

Q13. During WFI system qualification, what is the purpose of conducting worst-case challenge testing for the distribution loop?

• To validate that the loop can be cleaned only under ideal conditions
• To demonstrate system robustness under maximum stress conditions like highest flow, longest deadlegs and highest contamination risk
• To reduce the frequency of future sampling
• To verify material compatibility at ambient temperature only

Correct Answer: To demonstrate system robustness under maximum stress conditions like highest flow, longest deadlegs and highest contamination risk

Q14. Which of the following is a common indicator that biofilm is present in a WFI loop?

• Consistent low TOC values
• Regularly low heterotrophic plate counts
• Intermittent spikes in microbial counts and TOC with stable conductivity
• Immediate increase in conductivity only

Correct Answer: Intermittent spikes in microbial counts and TOC with stable conductivity

Q15. According to good practice, where should routine microbiological and endotoxin samples be taken in a WFI system?

• Only at the distillation unit outlet
• At multiple representative points including storage tank, recirculation loop, and point-of-use
• Only from the final point-of-use just before product contact
• Only from the feed water source

Correct Answer: At multiple representative points including storage tank, recirculation loop, and point-of-use

Q16. What effect does high dissolved oxygen typically have on WFI systems if not controlled?

• It reduces the risk of corrosion
• It promotes microbial growth and increases corrosion of metal surfaces
• It improves TOC monitoring sensitivity
• It increases conductivity significantly

Correct Answer: It promotes microbial growth and increases corrosion of metal surfaces

Q17. When validating a chemical sanitization cycle for WFI distribution, what must be demonstrated?

• The sanitant does not require rinsing after use
• The cycle reduces microbial load to acceptable levels and residues are removed or non-interfering
• The sanitant increases TOC to measurable levels permanently
• The sanitant will sterilize the water chemically for product use

Correct Answer: The cycle reduces microbial load to acceptable levels and residues are removed or non-interfering

Q18. For pharmaceutical WFI, why is stainless steel (316L) commonly specified for piping and storage tanks?

• It is the cheapest available metal
• It provides corrosion resistance, smooth welds, and supports sanitation and cleanability
• It spontaneously adsorbs organic contaminants
• It is magnetic which aids sampling

Correct Answer: It provides corrosion resistance, smooth welds, and supports sanitation and cleanability

Q19. Which control measure helps to minimize recontamination risk when transferring WFI from the storage tank to point-of-use?

• Allowing frequent tank venting without filtration
• Using closed-loop recirculation with sterile final filters at critical points
• Intermittent shutdown of recirculation to save energy
• Installing open transfer lines for easy access

Correct Answer: Using closed-loop recirculation with sterile final filters at critical points

Q20. Why is trend analysis of conductivity and TOC data important in WFI system monitoring?

• It replaces the need for routine microbiological testing
• It helps detect gradual deterioration, early contamination events or system failures before product impact
• It provides absolute proof of sterility
• It is only used for regulatory filing and not for day-to-day operation

Correct Answer: It helps detect gradual deterioration, early contamination events or system failures before product impact

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