Transformation of dissolved organic matter during ozonation: effects on trihalomethane formation potential

Transformation of dissolved organic matter (DOM) during ozonation results in a higher reduction in trihalomethane formation potential (THMFP) relative to dissolved organic carbon (DOC). This study was conducted to determine the effect of DOM transformation after ozonation on THM formation and to elucidate the difference in THMFP and DOC removal. Changes in DOC, THMFP, reactivities of the hydrophilic and hydrophobic DOC, and phenolic-OH were determined to explain the difference in THMFP and DOC removal after ozonation. Higher reduction in THMFP (24-46%) relative to DOC (10-16%) was obtained and was attributed to the following: transformation of DOM from a more reactive hydrophobic DOC (microg THM produced per mg organic carbon) to a less reactive hydrophilic DOC and to the decrease in the reactivities of both the hydrophobic and hydrophilic DOC after ozonation. The results also showed decrease in phenolic-OH indicating the oxidation of some reactive sites like resorcinol or meta-dihydroxy benzene ring structures, which are prone to chlorine substitution, consequently decreasing the reactivity of the organic carbon to form THM. These changes in DOM led to a significant decrease in THMFP with no remarkable removal in DOC.