Pluris Wedgefield, Inc., detected elevated levels of disinfectant by-products (DBP) of total trihalomethanes (TTHM) and haloacetic acids (HAA5) in drinking water in March, 2016. Although Pluris was in compliance even with the elevated levels, a Florida Department of Environmental Protection (FDEP) approved pilot study was conducted to evaluate replacing chlorine with chlorine dioxide as the disinfectant to insure future levels remained below the federal EPA Stage 2 limits.
Pluris has successfully completed the study and based on the findings has applied for a permit modification with the FDEP to allow chlorine dioxide to serve as the primary disinfectant in drinking water, replacing chlorine. Chlorine dioxide does not form DBPs. A number of Florida utilities are experiencing elevated DBPs and have been aware of Pluris’ study. The utilities have approached Pluris requesting information for their evaluation at their drinking water facilities. In an effort to benefit all utilities in Florida, Pluris and its consultant Kimley-Horn Associates are presenting at the Florida section of the American Water Works Association (AWWA) in November. The team has also prepared an abstract for submission to the National AWWA conference in June, 2018. The abstract is presented in the following.
Florida Section of the American Water Works Association (AWWA) and National AWWA Annual Conference and Exposition Abstract
Saying Goodbye to DBPs: Chlorine Dioxide for Water Treatment and Disinfection
Authors: Lance Littrell, P.E. Kimley-Horn and Associates, Maurice Gallarda, P.E. Pluris Holdings, LLC; Joe Kuhns, Pluris Wedgefield, Inc.; Steve Romano, P.E. Kimley-Horn and Associates; Rhea Dorris, E.I. Kimley-Horn and Associates
One of the largest issues facing nationwide utilities today is the reduction of disinfectant byproducts to comply with the federal Environmental Protection Agency Stage 2 Disinfection Byproduct (DBP) Rule. Current treatment methods of DBP precursor reduction such as membrane treatment, ion exchange and granular activated carbon treatment can incur significant capital and operational expenses. Other utilities have turned to chloramine disinfection to minimize the DBP formation which has its own routine challenges maintaining distribution systems. As an alternative, chlorine dioxide disinfection has shown to be effective in reducing DBPs within distribution systems. Chlorine dioxide is a powerful, selective oxidizer frequently used in paper and food processing industries. It does not react with organics to form TTHMs, making it an attractive option for enhancing water quality. Either as a primary disinfectant or a pre-oxidation treatment followed by free chlorine, chlorine dioxide testing results have proven favorable toward significant reduction of DBPs.
Wedgefield is a residential community in an unincorporated area of Orange County, Florida. Wedgefield’s Utility provider, Pluris Wedgefield, Inc., sought to reduce DBP formation in the community. Following preliminary testing and Florida Department of Environmental Protection approval, the Utility decided to implement a full-scale pilot test within the distribution system at Wedgefield’s Water Treatment Plant. The pilot testing indicated a 95%-99% reduction in TTHMs and 50% reduction in HAA5s. The pilot highlighted several relationships that are important to address when implementing chlorine dioxide such as chlorite and chlorine dioxide analyzers, chlorine impacts on chlorite formation, chlorine dioxide residual maintenance, and formation of disinfection byproducts. Each of these items will be detailed with supporting data to conclude the relationships experienced at this facility.
With the success of multiple laboratory studies and pilot testing, a chlorine dioxide application system is currently being implemented for permanent construction at Wedgefield’s Water Treatment Plant. Several utility providers facing DBP issues hope to follow in Wedgefield’s footsteps. An important step, however, to making chlorine dioxide treatment a reality was navigating the state and federal regulatory framework. A major challenge included establishment of an equivalent minimum chlorine dioxide disinfection residual. It was also paramount to understand safety requirements for chlorine dioxide and to maintain positive public perception.
The results of completed and ongoing pilot studies for various Florida utility providers have indicated that chlorine dioxide as a disinfectant was effective in maintaining disinfectant residuals as well as improving aesthetics in distribution system water quality. Chlorine dioxide has shown promise as an effective disinfectant chemical for other utilities aspiring to reduce DBPs without incurring significant capital cost associated with high-end treatment or the routine maintenance challenges with chloramines.
