What does the term "combined chlorine" refer to?

The term "combined chlorine" specifically refers to chloramines that are formed when free chlorine reacts with organic matter present in the water. This reaction produces compounds that are not as effective as free chlorine in disinfection, but they can contribute to water treatment by stabilizing chlorine levels and offering residual disinfection properties.

When free chlorine is introduced to water, it can react with nitrogen-containing compounds such as amino acids and proteins. This combination forms chloramines, which include monochloramine, dichloramine, and trichloramine. These compounds are classified as "combined chlorine" because they are not available as free chlorine in the water and contribute to the overall chlorine levels but do not possess the same disinfection potency.

Understanding combined chlorine is important for water treatment processes, as monitoring its levels helps prevent the formation of disinfection by-products and ensures effective water quality management.