Disinfection Processes Flashcards
7 cards from real Wastewater Operator Certification practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Disinfection Processes flashcards as text
At what approximate wavelength does UV radiation most effectively inactivate microorganisms?
Answer: 254 nm
UV radiation at approximately 254 nm is most effective because it falls within the peak absorption range of DNA and RNA, maximizing nucleic acid damage in microorganisms.
What is the primary mechanism by which UV disinfection inactivates microorganisms?
Answer: Damaging DNA and RNA, preventing reproduction
UV radiation causes the formation of thymine dimers and other photoproducts in DNA/RNA, preventing replication and rendering organisms unable to reproduce.
Which effluent quality parameter most significantly limits UV disinfection performance?
Answer: Turbidity and UV transmittance (UVT)
Turbidity and low UV transmittance shield microorganisms from UV exposure, directly reducing the delivered UV dose and disinfection efficacy.
A major operational advantage of UV disinfection over chlorination is:
Answer: No chemical residual or formation of harmful disinfection byproducts
UV disinfection adds no chemicals to the effluent, eliminating concerns about chlorine toxicity to aquatic life and the formation of disinfection byproducts like trihalomethanes.
Why must ozone (O₃) used for disinfection be generated on-site?
Answer: It is an unstable gas that decomposes rapidly and cannot be stored
Ozone has a very short half-life (approximately 20-30 minutes in water) and cannot be stored or transported, requiring on-site generation from oxygen or air.
Against which pathogen does UV disinfection have a significant advantage over conventional chlorination?
Answer: Cryptosporidium parvum oocysts
Cryptosporidium oocysts are highly resistant to chlorine at typical treatment doses but are effectively inactivated by UV irradiation at relatively low UV doses.
What is the primary operational disadvantage of ozone disinfection compared to chlorination for wastewater reuse applications?
Answer: Ozone provides no persistent residual disinfection after treatment
Ozone decomposes rapidly and provides no measurable residual in the treated effluent, offering no protection against recontamination during storage or distribution.