What is the purpose of adding sodium hexametaphosphate to the feedwater of an RO system?

Adding sodium hexametaphosphate to the feedwater of a reverse osmosis (RO) system primarily serves the purpose of decreasing calcium sulfate precipitation. In water treatment systems, particularly those utilizing RO technology, hardness minerals such as calcium and sulfate can form scale on the membrane surfaces. This scaling not only reduces the efficiency of the membrane but can also lead to membrane damage and increased operational costs.

Sodium hexametaphosphate acts as a threshold inhibitor for calcium sulfate by interfering with crystal growth and aggregation. This means it helps to keep these minerals in solution rather than allowing them to precipitate and form scale. By minimizing scaling, sodium hexametaphosphate contributes to the longevity and effectiveness of the RO membranes, ensuring they operate at optimal performance.

While enhancing water quality, preventing biofouling, and increasing water pressure are important aspects of water treatment systems, they are not the primary role of sodium hexametaphosphate. Its specific chemistries are designed to control scaling and improve the operational reliability of RO systems.