Oxidation kinetics of algal-derived taste and odor compounds during water treatment with ferrate(VI)

Abstract

The potential of ferrate(VI) to oxidize algal-derived taste and odor (T&O) compounds during water treatment was assessed by investigating the reaction kinetics of ferrate(VI) with selected T&O compounds. Apparent second-order rate constants (kapp) were determined in phosphate buffered waters in the pH range of 6 - 9. The olefinic T&O compounds show an appreciable reactivity to ferrate(VI): kapp = 34 to 639 M-1 s-1 at pH 7. The non-olefinic T&O compounds such as geosmin and 2-methylisoborneol show negligible reactivity to ferrate(VI) (kapp < 0.3 M-1 s-1). The reactivity of olefinic T&O compounds toward ferrate(VI) is poorly correlated with the Taft sigma constant as a descriptor of the olefin’s substituents while the high reactivity is found for the carbon double bond of alpha, beta-unsaturated carbonyl groups. The elimination rate of the olefinic T&O compounds during ferrate(VI) treatment was significantly enhanced with increasing ferrate(VI) dose, in which the enhancement was more than the model prediction that considers the ferrate(VI) reaction alone. Aldehydes were formed from the ferrate(VI) oxidation of olefinic T&O compounds indicating the double bond cleavage as one of the major oxidation pathways. Oxidation experiments in lake and river water matrixes spiked with selected T&O compounds confirmed the efficient elimination of olefinic T&O compounds.