Which of the following accurately lists the four most common disinfectants used in water treatment?

• A. Chlorine, Ultraviolet, Ozone, Peracetic Acid
• B. Chlorine, Ultraviolet, Ozone
• C. Ultraviolet, Ozone, Peracetic Acid
• D. Chlorine, Peracetic Acid

Answer: (A)

Disinfection options in water treatment are chosen to address different needs and conditions, so a mix of methods that covers chemical, residual, and physical pathways is common. Chlorine is the traditional workhorse because it provides a lasting residual disinfectant in the distribution system, helping to keep water safe after treatment. Ultraviolet light offers strong disinfection without adding chemicals, which is useful when you want to avoid disinfection byproducts or when you need quick microbial kill in a well-treated, clear water stream. Ozone is a powerful oxidant that inactivates a wide range of microorganisms and also helps with taste and odor issues, though it doesn’t leave a long-lasting residual unless combined with other steps. Peracetic acid is another disinfectant that can be used for rapid disinfection and is favored in some plants to reduce reliance on chlorine or to handle specific contaminants, with the byproducts generally breaking down into relatively benign substances.

Together these four represent a broad, versatile toolkit that many water treatment facilities rely on, spanning chemical and physical mechanisms and enabling operators to tailor disinfection to plant design, water quality, and regulatory or byproduct considerations. While other disinfectants exist, this combination is commonly emphasized in training because it covers the major, widely used approaches.