Monday, September 9, 2024
2:00 PM - 2:30 PM
Location Name
Chlorine Dioxide Treatment for Nitrification Control at Louisville Water: A Full-Scale Experience

Like many water utilities which use chloramine as a secondary disinfectant, Louisville Water experiences seasonal challenges with nitrification control in parts of its over 4,000 miles of distribution system. Nitrification is a serious issue for chloraminated systems, since it often results in loss of chlorine residual, which can lead to compliance and other water quality concerns. Since 2004, Louisville Water has conducted research into nitrification control treatment options, and this research has shown that low levels of chlorite (0.2-0.4 mg/L), a disinfection by-product of chlorine dioxide (ClO2), are effective in inhibiting nitrification in distribution systems. Louisville Water utilized this treatment by applying chlorite in localized regions of the distribution system, and while the chlorite was effective in those regions, it could not adequately address the system-wide nitrification issue that was experienced in recent years in the B.E. Payne (BEP) Plant distribution system. To address this new challenge, Louisville Water conducted an internal study and determined that the application of chlorine dioxide treatment at BEP Plant is a best-practical option for system-wide nitrification control. The study also identified the coagulation basins at BEP Plant to be the ideal ClO2 application locations for the high chlorite conversion and additional water-quality benefits, such as lowering chlorine demand and increasing Mn removal. A three-chemical chlorine dioxide generation system was then built and installed at BEP Plant by the summer 2023 and chemical feed began on October 31, 2023. This presentation will focus on the start-up and initial performance of the full-scale ClO2 system. Preliminary results demonstrate that ClO2 treatment is highly effective in system-wide nitrification control and overall water-quality improvement. At a ClO2 dose of 0.3 mg/L, a chlorite level of 0.2 mg/L in the finished water was obtained. Within a week of startup, BEP’s distribution system realized a stabilized chloramine residual, indicating effective inhibition of nitrification. The stable residual also allowed Louisville Water to lower the chlorine and ammonia doses at BEP Plant, both saving chemical costs and reducing DBP formation. The results of monitoring also confirmed that the application of ClO2 at the coagulation basins achieved the desired and stable chlorite residual with minimal chlorate formation. This presentation will discuss the background research that led to this treatment approach and the results of the chlorine dioxide startup in greater detail, including issues encountered during the project. Special attention will be given to the treatment impact on distribution water quality, analytical issues, and lessons learned from the startup.