The goal of this paper is to compare the performance of an in-line direct filtration (no flocculation) process with a dissolved air flotation (DAF) and filtration process for drinking water treatment. Both processes were studied at the pilot scale and included biologically active dual media (GAC/sand) rapid filters. Specific attention is given to the fate of organic matter. Organic matter was analyzed by measurements of dissolved organic carbon (DOC), assimilable organic carbon (AOC), disinfection by-product formation potential (DBPFP) and ultraviolet absorbance at 254 nm (UV254). In general, flotation removed a large fraction of organic matter with additional removal provided by biologically active filters. Most of the work occurred with ozonation of the raw water (pre-ozone). Ozone increased the biologically assimilable fraction of the water; filtration decreased this fraction to acceptable levels. Overall, effects of ozone on other organics are relatively small.

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