When does chlorine demand become satisfied?

Chlorine demand is satisfied when chlorine has reacted with all available organic and inorganic materials present in the water. This includes reacting with contaminants such as bacteria, viruses, organic matter, and metals. Once chlorine has completely reacted with these substances, it will be in a state where it is no longer available to perform additional disinfection or oxidizing tasks.

At this point, any remaining chlorine would be free chlorine, indicating that the initial demand for chlorine has been met. This is crucial for effective water treatment because it ensures that the water has not only been disinfected but that there is also a sufficient residual amount of chlorine to provide ongoing protection against pathogens.

While eliminating bacteria is part of the overall chlorine demand, satisfying chlorine demand specifically refers to the completion of the chemical reactions that consume chlorine. The concept of chlorine evaporating or reaching a residual of zero does not directly address this interaction and its implications for water quality and treatment efficacy.