What type of chlorine is produced during the fourth phase of chlorination?

During the fourth phase of chlorination, free residual chlorine is produced. This phase occurs after the initial disinfection processes have effectively utilized chlorine to kill or deactivate pathogens in the water. At this stage, the chlorine that remains in the water is not combined with other substances; rather, it exists in its more active form, which is capable of continuing to provide disinfection throughout the water distribution system.

Free residual chlorine is significant because it ensures that a disinfecting concentration of chlorine is sustained in the treated water, protecting it from microbial regrowth as it travels through the distribution network. This free chlorine persists because it has not reacted with ammonium or organic materials that would form combined chlorine, nor has it been entirely consumed in the disinfection process.

The distinction between free and combined chlorine is important for operators, as monitoring free residual chlorine levels is crucial for assessing the effectiveness of disinfection over time and ensuring water quality meets safety standards. Furthermore, while chlorinated organics and hydrochloric acid are byproducts and products from chlorination processes, they do not represent the residual disinfecting capacity of the chlorination system necessary for maintaining safe water.