Size exclusion chromatography for the characterization of dissolved organic fractions across drinking water unit processes

Dissolved organic matter (DOM) is of great concern because it influences many aspects of drinking water treatment, especially the formation of undesired disinfection by-products (DBPs) when disinfectant is applied. Samples were collected from 7 full scale WTPs employing a wide range of unit process, but receiving similar raw water supplies. DOM was examined by size exclusion chromatography combined with inline DOC detector (SEC-DOC) for better understanding of the organic fractional removal undergoing conventional processes or activated carbon (AC) contactor. The fractions with medium molecular weight (MW) (1,000-10,000 Da) and low molecular weight (<1,000 Da) were the major ones in all stages of the water treatment processes. Conventional treatment processes (coagulation/sedimentation/filtration) effectively removed colloidal and high-MW organics (MW>10,000 Da). Biologically active filtration also removed colloidal and high-MW organics. Deep bed GAC contactor removed medium-MW (humic acid and fulvic acid mostly) and low-MW organics (MW<1,000 Da) by 50 to 70% more after filtration. Adding powder activated carbon (PAC) (∼20ppm) could aid in reducing 20 to 40% more of medium- and low-MW organics before sedimentation. Coagulation reduced membrane fouling by removing colloidal and part of medium MW organics. The results suggested that drinking water facilities should apply GAC or other advanced techniques in order to effectively reduce DBP formation in drinking water. 2011