During water disinfection, natural organic matter reacts with chlorinated reagents to produced harmful byproducts, yet the formation and nature of those byproducts are poorly known. Therefore, scientists have focused on the fractionation of natural organic matter with membranes or resins to better understand how and which organic matter fractions react during chlorination. Here we compared the reactivity of disinfection by-products for various organic fractions with a meta-analysis of data from 400 water samples published in 80 publications, with focus on chlorination time and dose, (SUVA 254 ) and the column capacity factor used during resin fractionation. SUVA 254 refer to speci c ultraviolet absorbance at 254 nm divided by the organic matter concentration. We found that hydrophobic compounds have 10-20% higher reactivity to both trihalomethane and haloacetic acid formation, compared to hydrophilic compounds in waters with high SUVA 254 above 2 L/(mg•m), while hydrophobic and hydrophilic compounds have equal reactivity in waters with low SUVA 254 . On the other hand, hydrophilic compounds are 20-80% more reactive towards emerging disinfection by-products, regardless of SUVA 254 .Chlorination time and dose does not in uence the reactivity ratio between the different fractions. An increase in column capacity factor can shift the reactivity ratio from hydrophobic to hydrophilic fractions. Dead-end, stirred cell ultra ltration membrane fractionation might not always produce sharply separated fractions, which is mainly due to fouling. Therefore, no clear correlation could be found between membrane fractions and all investigated disinfection by-product groups.

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