Effects of coagulation on the removal of natural organic matter, genotoxicity, and precursors to halogenated furanones

Abstract

Natural organic matter (NOM) in drinking water can react with disinfectants to form disinfection by-products (DBPs). Halogenated furanones are a group of emerging DBPs that can account for 20–60% of the total mutagenicity observed in drinking water. This study examined the impacts of bench-scale coagulation and subsequent chlorination on DBP formation as well as genotoxicity using three source waters located in Ontario, Canada. Two halogenated furanones 3-chloro-4-(dichloromethyl)-2(5H)-furanone (MX) and mucochloric acid (MCA) were analyzed; along with trihalomethanes (THMs), haloacetic acids (HAAs), and absorbable organic halides (AOX). NOM was quantified using liquid chromatography–organic carbon detection (LC–OCD). Measured MX and MCA formation was 6.9–15.3 ng/L and 43.2–315 ng/L following optimized coagulation and subsequent chlorination of the three waters tested. DBP formation and speciation were evaluated as a function of the specific NOM fractions present in the source waters. Humics, building blocks, and biopolymers were highly correlated with DBP formation. Correlations between DBPs were also investigated and a potential relationship between MCA and/or MX vs. HAAs was observed. MX was the only measured DBP that contributed to genotoxicity, representing less than 0.001% of AOX by mass but responsible for 40–67% of the genotoxic response in chlorinated Ottawa River water samples. Genotoxic potential decreased with alum dosages, signifying that coagulation was effective at removing genotoxic DBP precursors.