We know within the water treatment industry there is a tricky equilibrium in regards to cost and accuracy in chemical dosing. Regulatory agencies have shown that there is no tolerance for inaccuracy to the dosing and concentration of chemicals used for minimizing contaminating organic materials. There have been many different methods used in chemical dosing and control in the disinfection process at treatment facilities.
Generally, the use of either metering with double diaphragm/peristaltic or centrifugal pumps has been the most effective measure used. Traditionally, centrifugal pumps with variable frequency drives have not been used due to their inability to accurately control flows at the low levels needed for disinfection while still maintaining taste standards.
Recently, there was a case study conducted to see the performance differences between metal and thermoplastic control valves at a facility in the western part of the United States. They tried to see if v-notch control valves would be more accurate than standard stainless steel control valves. The results showed that the thermoplastic valve not only was more than 80 percent more accurate, but also was much more reliable than its metal counterpart. In addition to minimizing the potential for fines from the U.S. Environmental Protection Agency (EPA), the improved performance showed savings of 17,520 gallons of sodium hypochlorite at 8 percent concentration per year for each dosing system. The municipality has been using this technology at all five of its systems and has had a total savings of 87,600 gallons of sodium hypochlorite at a cost savings of nearly $64,000 per year. This study concluded that there was such a financial impact from the reduction of chemical usage and the minimized risk for EPA fines that the municipality switched its entire system to the thermoplastic application.
For more information about this case study, visit the thermoplastic valve website at http://www.plasticvalves.com/reference.html.