Assessing disinfection byproduct risks for algal impacted surface waters and the effects of peracetic acid pre-oxidation

Abstract

This study assessed the disinfection byproduct (DBP) risks of algal impacted surface waters and the effects of peracetic acid (PAA) pre-oxidation on DBP risks. Authentic samples from three eutrophic lakes were collected over a 13-week period during the algal bloom season. The formation of 11 DBPs (four trihalomethanes, four haloacetonitriles, two haloketones, and trichloronitromethane) in these samples was assessed under uniform formation conditions (UFC) approximating drinking water disinfection. Trihalomethanes formed in the greatest abundance (90–370 μg L⁻¹), followed by haloacetonitriles (6.5–87 μg L⁻¹), haloketones (0.4–11.4 μg L⁻¹), and trichloronitromethane (0.3–9.7 μg L⁻¹). Total chlorophyll, a common indicator of algal activity, was not found to correlate with DBP yields. On the other hand, the yields of trichloronitromethane and haloacetonitriles correlated with nitrite/nitrate concentrations and DON concentrations in the samples, respectively. PAA pre-oxidation reduced the formation of trihalomethanes in the subsequent UFC tests in 80% of the samples, but promoted the formation of haloacetonitriles and trichloronitromethane in 70% and 50% of the samples, respectively. Analyses of DOC, DON, SUVA, and fluorescence excitation–emission matrices suggest that PAA pre-oxidation can alter the DBP precursors of a sample through the release of high haloacetonitrile/trichloronitromethane-yielding organic matter from algal cells and the oxidative transformation of existing and newly released dissolved organic matter. The results of this study, obtained from authentic surface water samples, suggest that mixed organic matter dynamics is an important consideration for the DBP risks of algal-impacted waters.