AWWA JAW66306

The David L. Tippin Water Treatment Facility in Tampa, Florida, recently added ozonation and biologically activated carbon filtration and made additional modifications to its existing conventional treatment process. The facility treats water that has relatively high organic matter content, especially during high-rainfall seasons. After startup, unexpectedly low monochloramine formation efficiency and rapid decay of monochloramine residual in treated waters were observed. Similar problems associated with the rapid decay of residual disinfectant have been reported by other utilities. By changing the sequence of free chlorine and ammonia injection and providing sufficient mixing and reaction time for free chlorine, the authors were able to increase monochloramine formation efficiency. Filter backwashing was also modified to successfully enhance filter performance and stabilize monochloramine in treated waters. These findings and proposed solutions could be useful for many utilities experiencing similar problems or considering conversion to monochloramine. The study methods and results provided here could be used as a benchmark for other utilities to solve similar problems. Includes 35 references, tables, figures.