AWWA ACE65606

The City of Peoria's (City) Greenway Water Treatment Plant (GWTP) applies ozone followed by conventional flocculation/sedimentation and biologically active granular activated carbon (GAC) filters in treating its raw water. The GAC filters are used for removing particulates and in assisting in the removal of disinfection byproduct (DBP) precursors and taste and odor (T&O) compounds from raw water. Due to the presence of moderate levels of bromide in City's raw water, ozone dosages are kept to the minimum to keep the bromate level below the 10 micrograms/liter (µg/L) maximum contaminant level (MCL). By limiting the ozone dose, the City is not able to maintain ozone residual at ozone contactor or achieve disinfection credits with ozone. The City believes that the ozonation and biologically active GAC filtration processes can be further optimized to improve the removal of DBP precursors and T&O compounds while the bromate formation is controlled or minimized. The City is especially interested in further optimization for the following reasons: an optimized ozonation step will ensure reliable compliance with the bromate standard while increasing the disinfection ability for the unit process; improving the removal of total organic carbon (TOC) through the optimized operation of ozonation, coagulation and GAC filtration will reduce DBP concentrations in distribution system, in particular, total trihalomethanes (TTHMs); and, the optimized use of these combined processes will result in improving finished water quality in terms of lowering TOC, DBPs and T&O compounds. The City retained Malcolm Pirnie Inc. to conduct an evaluation to meet the following objectives: identify alternative methods to mitigate bromate formation during the ozonation process; and, conduct necessary bromate mitigation bench-scale tests and develop recommendations for full-scale consideration. Includes reference, tables, figures.