How breakpoint chlorination works in water treatment to remove chloramines.
Breakpoint chlorination is a process in water treatment where chlorine is added to water until all reactive substances, like ammonia and organic compounds, are oxidized, and a free residual chlorine level is achieved. This method ensures that the water is fully disinfected, without any chloramines or other byproducts that can cause unpleasant tastes, odors, or health risks.
Key Stages of Breakpoint Chlorination
When chlorine is added to water, it reacts with various impurities in a sequence of stages:
Initial Chlorine Demand:
When chlorine is first added to water, it reacts with reducing agents, such as iron, manganese, and hydrogen sulphide. This stage does not result in any free chlorine residual, as all the chlorine is consumed in these reactions.
Formation of Chloramines:
As more chlorine is added, it begins to react with ammonia (if present) to form chloramines (like monochloramine, dichloramine, and trichloramine). Chloramines provide some disinfection but are less effective than free chlorine and may impart an unpleasant taste or odour to the water.
Breakpoint:
Continued addition of chlorine oxidizes chloramines and other remaining compounds, eventually reaching a point where these reactions are complete. This is the “breakpoint,” where the chlorine demand has been satisfied, and any further addition of chlorine results in free chlorine residuals.
At this point, chlorine can exist as free chlorine in the water, which provides effective and long-lasting disinfection.
Free Chlorine Residual:
After reaching the breakpoint, any additional chlorine added remains in the water as free chlorine, which is highly effective for disinfection and provides a residual effect, ensuring ongoing protection against recontamination.
Why Breakpoint Chlorination is Important
Effective Disinfection: It ensures that all ammonia and organic compounds are oxidized, eliminating potential for chloramine formation, which can reduce the effectiveness of disinfection.
Improved Water Quality: It removes unpleasant odours and tastes associated with chloramines.
Residual Protection: It provides a stable residual of free chlorine in the water, ensuring continued disinfection throughout the distribution system.
Applications of Breakpoint Chlorination
- Drinking Water Treatment: Ensures safe, chloramine-free drinking water with a stable chlorine residual.
- Wastewater Treatment: Helps in disinfecting treated wastewater before release into natural water bodies.
- Swimming Pools: Used to ensure effective chlorination without forming irritating chloramines.
