On the Decomposition of Keto-carboxylic Acids in Water by Ozone Treatment and UV Irradiation

Abstract

Keto-carboxylic acids will be important decomposition intermediates when ketones or fatty acids contained in water are treated with ozone. In this report 5 mM keto acids in the 0.05 M phosphate buffer (pH 7.0) were treated with UV irradiation alone, ozone alone or ozone + UV irradiation, and their decomposition products and the degradation pathway were investigated. The degradation pathways of keto-dicarboxylic acids were considered to produce dicarboxylic acid by oxidative decarboxylation at 1-position carbonyl group, α-keto-dicarboxylic acid having one carbon atom decreased by oxidative decarboxylation at the other terminal carbonyl group, and glyoxylic acid and dicarboxylic acid by releasing an α-keto-carboxylic acid group. And the main degradation pathway of keto-monocarboxylic acids containing a carbonyl group at α-position was considered to produce a monocarboxylic acid having one carbon atom decreased by oxidative decarboxylation. Other pathways were involved in the production of glyoxylic acid and monocarboxylic acid by releasing α-keto-carboxylic acid group, and keto-dicarboxylic acids by oxidation at a terminal methyl group. The degradation pathways of keto-monocarboxylic acids having a ketone group except α-position were considered to release a longer side-chain part prior to the other shorter chain. The released chains were considered to produce monocarboxylic acids or dicarboxylic acids. These intermediate products will be decomposed gradually to CO2 and H2O. TOC (total organic carbon) removal (%) was very high by ozone + UV irradiation. By the way, keto acids themselves by UV irradiation alone were decomposed some, because they has UV absorption spectrum about 254 nm which is the main irradiation wavelength of low presser mercury lump. But the TOC removal (%) by UV irradiation alone or O3 alone was very low, because the decomposition products could not be decomposed by each treatment. These results will be utilized as important data when various ketones in the water are treated with O3 and UV.