AWWA JAW19157

Molecular size, charge, and solubility characteristics of dissolved organic carbon (DOC) in raw and coagulated water from a Virginia reservoir were investigated to determine the types of organic compounds removed by the conventional treatment sequence of coagulation, settling, and filtration. The largest factor was molecular weight distribution of the DOC. Precipitation of DOC by ferric sulfate coagulation was size-dependent, with a bias toward larger molecules. Charge was the secondary factor in DOC removal, with ionic compounds being selectively removed over neutral ones. Hydrophilic and hydrophobic organics were preferentially removed over compounds of intermediate solubility. Fulvic acids were the dominant precursors of trihalomethanes and total organic halides in untreated water because of their abundance, high specific yields, and fast reaction rates. These compounds were readily removable by coagulation. The dominant precursors in treated waters were low molecular weight neutral compounds. These compounds could not be precipitated by coagulation. Compared with fulvic acids, this precursor group had lower specific yields and slower reaction rates. Includes 43 references, tables, figures.