The application of ozone for disinfection or abatement of micropollutants during treatment of drinking water and wastewater is accompanied by ozone reactions with matrix components such as dissolved organic matter (DOM) which leads to the formation of undesired oxidation by-products (OBPs) such as low molecular weight aldehydes, ketones or quinones. To date, the identification of unknown carbonyl compounds in complex matrices remains a bottleneck in analytical chemistry. The objectives of this study were to (1) develop and optimize a method for the derivatization and non-target analysis of carbonyl compounds in different water matrices including solutions containing Suwannee River Fulvic acid (SRFA), surface water and wastewater and (2) apply the optimized method to investigate the formation of carbonyl compounds during ozonation of different water matrices as a function of the ozone doses including samples from a full-scale wastewater treatment plant operated at three different ozone doses. The method involves the derivatization of a wide range of saturated and unsaturated aldehydes, ketones and ketoacids using <i>p</i>-toluenesulfonylhydrazine (TSH) and analysis of signature fragments originating from the derivatizing agent by liquid chromatography coupled to electrospray ionization high-resolution mass spectrometry (LC-ESI-HRMS). The formation of selected carbonyl compounds including acetaldehyde, formaldehyde, pyruvic acid and glyoxylic acid during ozonation was detected by target analysis. These four compounds were quantified with concentrations up to 200 µg/L at a specific ozone dose of 0.5 mgO<sub>3</sub>/mgC in wastewater. The presence of carbonyl compounds in all of the DOC-normalized matrices increased from surface water &lt; SRFA &lt; wastewater. A similar trend across the matrices was observed for the non-target analysis where unknown carbonyl compounds also increased in area compared to non-ozonated samples. In total, the composition of over 100 unknown carbonyl compounds including N-containing carbonyl compounds was predicted. Among the tentatively identified compounds, the majority (~80 %) have not been reported previously. Structural elucidation will be performed on selected masses. Results provide new insights into the formation of carbonyl compounds, an important class of OBPs, during ozonation and the potential of this approach for applications to other oxidation processes.

Non-target screening of carbonyl compounds formed during ozonation of different water matrices

ACS Fall 2021

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