General Exam Questions Flashcards
The City of Toronto has asked you to complete a theoretical design for a new water treatment plant. What are three factors that you might consider when evaluating the treatment
processes to be included in the new facility?
Health effects, taste and odour thresholds, available treatment/control alternatives, and practical quantitation limits for parameters
When considering Stoke’s law, which parameter can treatment plant operators practically
control to most significantly improve settling? Briefly explain why this parameter is important
and how it can be controlled.
The settling velocity tank can be essentially controlled by designing the tank depth. Shallower tanks = a higher velocity, since it takes less time for the particle to travel to the bottom of the tank. Settling velocity because it allows us to compare it to the overflow rate and determine how many particles will be removed.
Ontario’s disinfection regulations require drinking water treatment plants to achieve 2-log (99%) removal or inactivation of Crvptosporidium. How is this removal/inactivation typically achieved, and how is it monitored?
Disinfection rules are established, and well operated plants receive credits for this 2-log removal of Cryptosporidium.
CT values are used to determine desired levels of disinfections based on the values presented in regulations.
d) Which form of free chlorine is the best disinfectant and at what pH does it become dominant’?
HOCl is the best disinfectant (it is much faster and 80-90 times more effective than OCl-) and is most dominant at pH between 6-7 for chlorine disinfection.
Provide two of the mechanisms that result in particle retention during filtration. Which of these
mechanisms can be directly controlled by a water treatment plant operator? How?
Transport mechanisms (interception, sedimentation, diffusion) - brings particle to media surface Attachment mechanisms - retains particle in media surface
Some ideas for which can be directly controlled:
- with smaller media sizes, you can adjust the spacing between media particles, ultimately influencing the interception transport mechanism
Why is the BOD5 test more commonly used than the ultimate BOD test?
- longer tests may be influenced by nitrification
- ultimate BOD tests are too time consuming
