What is the process called when chlorine is added to water until the chlorine demand has been satisfied?

The process of adding chlorine to water until the chlorine demand has been satisfied is known as breakpoint chlorination. This is a crucial step in water treatment because it ensures that all oxidizable materials, such as organic matter and ammonia, have reacted with the chlorine before any free chlorine remains in the water.

In breakpoint chlorination, maintaining a proper level of chlorine is essential to achieve effective disinfection. When the chlorine concentration is increased to a point where it exceeds the total chlorine demand (which includes reactions to oxidize contaminants), there is a point where the demand is fully satisfied, and free chlorine becomes available. This not only helps in the disinfection of pathogens but also improves water safety by ensuring that undesirable substances are eliminated from the water.

In contrast, the other processes mentioned serve different purposes. Continuous chlorination refers to a method of adding chlorine consistently to maintain a residual level for ongoing disinfection, while shock chlorination is an intensive treatment involving high levels of chlorine applied for a short time, usually to address specific contamination issues. Residual chlorination involves maintaining a certain level of chlorine in the water system for disinfection but does not specifically address the fulfilment of chlorine demand in the same way as breakpoint chlorination does.