AWWA JAW18746

Mississippi River water was subjected to various pretreatments (lime softening, alum coagulation, and iron-polymer coagulation) before being applied to columns of granular activated carbon (GAC). Samples were taken from the raw river water, after pretreatment, and after carbon adsorption. The organic content of these samples was characterized, indicating that 40 percent of the organics was hydrophobic and 60 percent as hydrophilic. Molecular weight distributions for the fractions less than or equal to 1K, 1-10K, 10100K, and greater than or equal to 100K were 23, 50, 10, and 17 percent, respectively, based on total organic carbon analyses. Pretreatment resulted in the removal of mainly acidic and neutral organic compounds. Hydrophobic organics were slightly better removed than hydrophilic compounds. Coagulation resulted in better organics removal, but lime addition was not optimized for organics removal. Trihalomethane precursors were almost evenly split between hydrophobic and hydrophilic fractions in the raw water. Hydrophobic precursors were more effectively removed during pretreatment. Significant differences in the character and distribution of THM precursors between limetreated and coagulated waters before and after GAC treatment were noted. Higher molecular weight organics were most effectively removed during pretreatment; lower molecular weight organics were effectively reduced by GAC. After lime treatment, the concentration of low molecular weight organics appeared to increase; coagulation had no significant impact on this fraction. The effluent samples from GAC contained mainly low molecular weight hydrophilic neutral and acidic organics. Includes 27 references, tables, figures.