Disinfection Processes Flashcards
7 cards from real WTO 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
Which of the following is a treatment technique violation under the Surface Water Treatment Rule (SWTR)?
Answer: Failure to maintain a detectable disinfectant residual throughout the distribution system
The SWTR requires systems to maintain a detectable disinfectant residual in the distribution system as a treatment technique to protect public health.
What is the purpose of the T10 value used in CT calculations?
Answer: The time for 10% of incoming water to pass through the contact chamber
T10 is the time for the first 10% of tracer mass to pass through the contact basin, representing a conservative estimate of actual contact time.
Which disinfectant is most effective at inactivating viruses at typical water treatment doses?
Answer: Free chlorine
Free chlorine provides excellent virus inactivation at typical doses and contact times, and is more effective than chloramines for this purpose.
A treatment plant is required to achieve 0.5-log inactivation of Giardia by disinfection. The source water temperature is 5°C and pH is 7.0. The operator should expect to need:
Answer: Higher CT than at 15°C because lower temperatures reduce disinfection efficiency
Cold water reduces the rate of chemical disinfection reactions, requiring higher CT values to achieve the same log-inactivation credit.
What is the maximum disinfectant residual level (MRDL) for chlorine in a public water system under the DBPR?
Answer: 4.0 mg/L
The DBPR sets an MRDL of 4.0 mg/L for chlorine as an annual average measured in the distribution system.
An operator detects a sudden spike in chlorine demand at the plant inlet. The most likely cause is:
Answer: Increase in organic matter, algae, or other oxidizable material in the source water
Elevated organic matter, algal blooms, or other reducing substances in source water dramatically increase chlorine demand, requiring higher doses to maintain a residual.
Which statement correctly describes the relationship between turbidity and disinfection?
Answer: High turbidity reduces disinfection efficiency by shielding pathogens from the disinfectant
Particles in turbid water can shield pathogens from disinfectants and consume disinfectant demand, reducing inactivation efficiency for both chemical and UV disinfection.