The Reactivity of Dissolved Organic Matter for Disinfection By-Product Formation

Dissolved organic matter (DOM) in 6 water samples collected from 4 surface waters were fractionated using some or all of 5 physicochemical separation processes (activated carbon and XAD-8 batch adsorption, alum coagulation, ultrafiltration (UF), and XAD-8 column fractionation). Activated carbon, XAD-8 batch adsorption and alum coagulation processes fractionated DOM by preferentially removing high-SUVA components from solution. The XAD-8 column method fractionated DOM into hydrophobic and hydrophilic components while UF separated DOM into different size fractions. Over 40 DOM fractions, characterized using carbon-normalized (specific) ultraviolet absorbance (SUVA), were obtained for each water. Trihalomethane (THM) and haloacetic acid (HAA9) formation after chlorination was quantified for each fraction. For each natural water, a strong correlation was observed between the SUVA values of DOM fractions and their THM and HAA9 formations, independent of the separation processes used to obtain the fractions. Therefore, the correlation obtained for each water appears to represent its natural disinfection by-product (DBP) reactivity profile. However, SUVA is not a universal predictor of DOM reactivity because a unique DBP reactivity profile was obtained for each water tested. The distribution of SUVA within a source water and its relationship to reactivity were found to be more informative than the source water aggregate SUVA value. Individual DBP species also correlated well with the SUVA of DOM fractions in a single water. Formation of trichloroacetic acid (TCAA) was dominant over dichloroacetic acid (DCAA) for high-SUVA fractions, whereas the formation of TCAA and DCAA was comparable for low-SUVA fractions.