Which of the following is a method of disinfection used in water treatment?

Chlorine dioxide is widely used in water treatment as an effective method of disinfection. It acts as a strong oxidizing agent and has the ability to eliminate a broad spectrum of pathogens, including bacteria, viruses, and protozoa. Its effectiveness is due to its molecular structure, which allows it to penetrate microbial cell membranes and disrupt vital cellular functions, thus ensuring the inactivation of harmful organisms present in the water.

Chlorine dioxide is particularly valued for its ability to provide disinfection without forming significant amounts of harmful disinfection by-products that can occur with some other disinfectants, such as chlorine. This makes it a preferred choice in many water treatment facilities, especially for surface water treatment and in situations where water quality is critical.

Other options may also play roles in water treatment but do not serve as primary disinfecting agents or have specific constraints. For example, iodine is a disinfectant, primarily used in smaller-scale applications and not common in large municipal systems. Hydrogen peroxide can be used for specific water treatment needs, primarily as an oxidant rather than a general disinfectant. Calcium carbonate is typically used to adjust water hardness and alkalinity rather than for disinfection purposes.