In 2014, the city of Franklin, NC, purchased a Chemtrac on-line Streaming Current Monitor at the advice of their state regulatory agency. This was to help them manage USEPA Maximum Contaminant Levels (MCL) for disinfection by-products.
Historically, plant operators determined their coagulant dosage based on the turbidity level in their river source. Both alum and lime were used to treat a cold, low alkalinity, and often turbid river influenced by heavy rain events. Lime dosages were calculated by the amount of alum being fed to the process, and operators increased both chemicals proportionally to keep the water chemistry balanced. Their methods worked well until the disinfection byproducts approached levels of concern. No longer would the “old tried and proven” methods work…Franklin WTP needed something new.
Using the Chemtrac Streaming Current Monitor, plant operators gained a new confidence in running their plant at lower pH levels, helping them remove more natural organic matter from the source water, and thereby reducing their disinfection byproducts. Operators also tried new coagulant blends that are less pH sensitive than alum, and more conducive to forming floc under cold water conditions. As a result, in 2015 the plant will employ a new PACl blend that demonstrated excellent filtered turbidity, and lower disinfection byproducts. Even though there will be unit cost ($/pound) increases from switching to the new coagulant, the plant is confident that their streaming current monitor will maintain proper chemical dosages based on the quality of their incoming water, optimizing the coagulation process, and minimizing the overall cost of treating the water.