When should phosphates be added in relation to chlorine?

Phosphates should be added before chlorine in the water treatment process to improve water quality and enhance chlorine's effectiveness. The purpose of adding phosphates is to help prevent the formation of chlorinated byproducts and to stabilize inorganic compounds in the water. When phosphates are introduced prior to the addition of chlorine, they can help to create a protective lining on the surfaces within the distribution system, which can reduce the potential for corrosion and assist in maintaining optimal water quality.

Adding phosphates after chlorine could interfere with the disinfection process because the chlorine may be less effective in killing pathogens if phosphates are present in excess, leading to suboptimal treatment outcomes. Similarly, adding them simultaneously can lead to unpredictable reactions and less effective disinfection. Therefore, the proper sequence—adding phosphates prior to chlorine—ensures that both agents can work together effectively while minimizing any negative interactions.