At what point should polyphosphates be fed into the water treatment process?

Feeding polyphosphates into the water treatment process before the addition of chlorine is crucial for several reasons. Polyphosphates are commonly used as a sequestrant in water treatment to prevent the precipitation of hardness minerals, such as calcium and magnesium, and to help maintain the solubility of iron and manganese. When added before chlorine, polyphosphates can effectively bind these metals, reducing the likelihood of them interfering with the disinfection process.

If polyphosphates are added after chlorine, the interaction with chlorine could potentially lead to undesirable reactions, such as the formation of chlorinated byproducts and reduced effectiveness of the chlorine in disinfection. Furthermore, if metals are not adequately sequestered before the introduction of chlorine, they could precipitate during the chlorination phase, leading to inefficiencies in the treatment process.

In terms of the other options, adding polyphosphates at the source supply might not be practical for achieving optimal treatment, as the effectiveness of the sequestering properties can be influenced by interaction times and conditions present in the treatment process. Adding them during filtration may not allow sufficient time for the polyphosphates to interact with hardness minerals properly. Thus, incorporating polyphosphates into the treatment process before chlorine addition