Reduction of Disinfection Byproduct Formation by Molecular Reconfiguration of the Fulvic Constituents of Natural Background Organic Matter

Abstract

Experiments were performed to assess the effects of treating the fulvic acid fractions of background natural organic matter (NOM) by catalyst-induced oxidative coupling reactions. Changes in the molecular characteristics of the fulvic acids and related disinfection byproduct formation potentials of these important NOM constituents were investigated. The coupling reactions were induced by addition of horseradish peroxidase (HRP) and hydrogen peroxide to aqueous solutions of the fulvic acids (FAs) in semicontinuous flow reactors. Subsequent removal of organic matter by ultrafiltration was found to be markedly enhanced for FA solutions subjected to oxidative coupling treatment. Uniform formation condition tests further indicated that the disinfection byproducts formed upon chlorination of FAs treated via induced oxidative coupling were reduced significantly on a unit carbon basis relative to those formed upon chlorination of their untreated counterparts. Spectroscopic examinations revealed thatthe FA molecules were effectively reconfigured in the oxidative coupling reactions. Substantial conversion of aromatic hydroxyl groups into ether-bonded moieties is evident, and a loss of primary amine groups, probably through conversion into secondary or tertiary amines, was also observed. These conversions apparently result in cross-linking of the natural FA moieties to form stable species of larger sizes, thus rendering them more readily removable by ultrafiltration and less reactive with chlorine. The results of the study may be interpreted as indicating that catalytically induced oxidative coupling reactions of the type conducted in this work can be combined with ultrafiltration to provide an effective scheme for removal of disinfection byproduct precursors.