Molecular Alterations of Algal Organic Matter in Oxidation Processes: Implications to the Formation of Disinfection Products

Seasonal algal blooms in surface waters can adversely impact drinking water quality. Oxidative treatment has been demonstrated as an effective measure for the removal of algal cells. However, this, in turn, leads to the release of algal organic matter (AOM). Effects of oxidative treatment using chlorine, bromine, chloramine, ozone, and permanganate on the molecular alterations of the AOM were studied using Fourier transform ion cyclotron resonance mass spectrometry. Increased chemodiversity, decreased aromaticity, and elevated average oxidation state of carbon () were observed after oxidation. Of the oxidants, ozone caused the most pronounced changes. There was a positive correlation between the increases in and reduction potentials of oxidants (i.e., ozone > chlorine ≈ bromine > permanganate > chloramine). Oxygen transfer and oxidative dehydrogenation were major pathways (42.3-52.8%) for AOM oxidation, while other pathways (e.g., deamination, dealkylation, decarboxylation, and halogen substitution/addition) existed. Moreover, the halogen substitution/addition pathway only accounted for 1.3-10.3%, even for chlorine or bromine treatment. Oxidative treatment could decrease the reactivity of AOM in postchlorination, thereby decreasing the trichloromethane formation. However, the formation of oxygen-rich disinfection byproducts (DBPs, e.g., trichloronitromethane) could be favored, especially for ozonation. This study provides molecular-level insights into the effects of oxidative treatment on AOM and derived DBP formation in water treatment.