AWWA JAW10840

This article describes a study carried out in part to obtain more data on removal of trihalomethane (THM) precursors by granular activated carbon (GAC) filters. The principal objectives of the project were as follows: to test, on a pilot scale, traditional treatment including coagulation, sedimentation, and rapid mixed-media filtration, ozonation in a turbine contractor with short contact time, followed by a longer residence time in contact with residual ozone, and GAC adsorption in packed beds operated in a downflow mode, with and without preozonation for the removal of THM precursors, from a southern US reservoir that has high levels of natural organics; to determine the populations of bacteria in the GAC filters and the role these bacteria play in the removal of organic substances vis-a-vis pure adsorption processes; and to evaluate the capital and operating costs for the addition of GAC filters to existing US water treatment plants such as those supplied from the source of water for this study. Results show that GAC columns may be operated for extended lifetimes by optimizing the physical and microbiological processes that occur within these columns. With THM formation potential as the principal analytical criterion, the source water for this experiment was treated to meet the 0.10 mg/L maximum contaminant level (MCL) for more than one year by using a combination of alum flocculation, mixed-media filtration, and GAC adsorption. Includes 20 references, tables, figures.