Combined chlorine in water treatment refers to what?

Combined chlorine in water treatment specifically refers to the form of chlorine that has reacted with organic materials, like ammonia or nitrogen compounds, to form chloramines. This occurs when chlorine is used for disinfection, and it binds with these organic compounds rather than remaining as free chlorine, which is the active form of chlorine available for disinfection.

When chlorine is added to water, it can exist in three forms: free chlorine, combined chlorine, and total chlorine. The combined chlorine is particularly important to monitor because it is less effective as a disinfectant compared to free chlorine. Recognizing the presence of combined chlorine helps water treatment professionals evaluate the effectiveness of disinfection processes and ensure water safety.

The incorrect choices highlight different aspects of chlorine's chemistry but do not accurately define combined chlorine. Chlorine gas dissolved in water represents the free chlorine aspect, elemental chlorine refers to the unreacted form, and chlorine reacting with minerals would pertain to interactions not related to organic compounds.