What are the two common disinfection methods used in wastewater treatment plants and a basic principle of each?

• A. Chlorination (chemical disinfection using chlorine or chloramines) and UV disinfection (inactivates microorganisms with ultraviolet light).
• B. Aeration and filtration.
• C. Ozone disinfection only.
• D. UV disinfection using chlorine.

Answer: (A)

Disinfection in wastewater treatment is about inactivating microorganisms so the effluent is safe for the environment. The two common methods are chlorination and UV disinfection.

Chlorination involves dosing chlorine or chloramines into the treated water. The disinfecting effect comes from chemical oxidation that damages cell walls, enzymes, and nucleic acids of pathogens, preventing them from functioning. Chlorination also leaves a residual disinfectant, which helps keep the water microbiologically protected as it moves through any subsequent treatment steps or receiving waters.

UV disinfection uses ultraviolet light, typically UV-C, to injure the genetic material of microorganisms. This prevents them from reproducing and effectively "kills" them by stopping their ability to cause infection or contamination. UV has no chemical residual and relies on clear water; turbidity or color can reduce its effectiveness, and routine maintenance is needed to keep lamps clean and functioning.

Other options listed aren’t the standard pairing used for disinfection. Aeration and filtration target solids, odors, and some stability of the waste, not pathogen inactivation. Ozone is a disinfectant in some plants, but it’s not the two most common methods described for routine disinfection. And UV disinfection does not involve chlorine at all; they are separate approaches.