Effect of NOM and lime softening on Geosmin removal by PAC

Geosmin is a commonly occurring taste and odor compound that imparts an earthy/musty odor to drinking water even at very low concentrations (odor threshold concentration, 4-20 ng/L). In this research, jar tests were performed to determine the effect of natural organic matter (NOM) and lime softening on geosmin removal via powdered activated carbon (PAC). NOM significantly inhibited geosmin sorption to PAC. For Suwannee River NOM, geosmin removal efficiency decreased by 2.7% for every 1 mg/L increase in dissolved organic carbon concentration at a PAC dose of 7.5 mg/L. Comparing three Suwannee River organic matter types, the extent of inhibition increased as average molecular weight decreased, suggesting that smaller NOM compounds are primarily responsible for inhibiting geosmin sorption to PAC. Surprisingly, lime softening did not affect geosmin removal by PAC; thus, maximizing PAC contact time, regardless of when the lime or coagulants are added, should provide the greatest geosmin removal.