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
What is the primary purpose of disinfection in wastewater treatment?
Answer: Inactivate pathogenic microorganisms
Disinfection targets the inactivation or destruction of pathogenic microorganisms to protect public health and receiving water bodies.
Which form of chlorine is the most effective disinfectant in wastewater treatment?
Answer: Hypochlorous acid (HOCl)
Hypochlorous acid (HOCl) is the most germicidal form of chlorine because it is an uncharged molecule that penetrates cell membranes more easily than the hypochlorite ion.
At what pH does hypochlorous acid (HOCl) predominate over the hypochlorite ion (OCl⁻)?
Answer: Below pH 7.5
Below pH 7.5, the equilibrium strongly favors HOCl, making lower pH conditions more favorable for chlorine disinfection effectiveness.
The CT value used in disinfection calculations represents:
Answer: Disinfectant concentration (mg/L) multiplied by contact time (minutes)
CT is the product of residual disinfectant concentration (C) and the hydraulic contact time (T), used to predict pathogen inactivation efficacy.
What occurs at the breakpoint in breakpoint chlorination?
Answer: Enough chlorine has been added to destroy all chloramines, producing a free chlorine residual
At breakpoint chlorination, all ammonia-nitrogen has been oxidized and combined chlorine (chloramines) have been destroyed; any additional chlorine added appears as free chlorine residual.
Chlorine demand is defined as:
Answer: The difference between the chlorine applied and the free chlorine residual remaining
Chlorine demand is the quantity of chlorine consumed by reactions with organics, ammonia, and other reducing substances, calculated as applied chlorine minus residual chlorine.
Which disinfectant is most widely used in US municipal wastewater treatment plants?
Answer: Chlorine gas or sodium hypochlorite
Chlorine (as gas or sodium hypochlorite) is the most widely used disinfectant in US wastewater plants due to its effectiveness, low cost, and ability to provide a measurable residual.