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Joanna Houska lors de la remise du prix avec le Prof. Thomas Ternes au congrès annuel de la Wasserchemische Gesellschaft à Limburg (D) (Photo: Nina Hermes, BfG).

L’oxydation, mais de manière maîtrisée - une thèse primée

17 juillet 2024 | Andri Bryner

La chimiste de l’environnement Joanna Houska a été récompensée pour sa thèse de doctorat par la Deutsche Wasserchemische Gesellschaft (Société allemande de Chimie de l’Eau). Joanna Houska a mené des recherches à l’Eawag et à l’EPFL, et a démontré tant théoriquement qu’expérimentalement comment le traitement oxydatif de l’eau avec de l’ozone ou du chlore peut être utilisé de manière plus efficace lorsqu’on connaît plus précisément les substances organiques dissoutes dans l’eau à traiter

«Ce travail est un jalon vers une meilleure compréhension du rôle de la matière organique dissoute dans le traitement oxydatif de l’eau», déclare Urs von Gunten, le directeur de thèse de Joanna Houska. Il est professeur à l’EPFL et dirige à l’Institut de recherche de l’eau Eawag le groupe Chimie de l’eau potable. Selon von Gunten, Joanna Houska possède «une énorme capacité à traiter des questions scientifiques complexes de manière théorique et expérimentale et à résoudre des problèmes avec une grande indépendance.» Dans ses expériences, mais aussi grâce à la modélisation, la chercheuse a produit et interprété de nouvelles données passionnantes qui peuvent être utilisées pour améliorer le traitement oxydatif de l’eau.

Inefficace et dangereux sans analyse précise

Quel est donc le problème? Lorsqu’on utilise du chlore ou de l’ozone pour la désinfection/l’oxydation de l’eau, le principal objectif est de neutraliser les germes pathogènes et les micropolluants. Mais la majeure partie des agents oxydants réagit avec les composants de la matrice de l’eau, tels que la matière organique dissoute. Cela réduit non seulement l’efficacité des procédés, mais peut aussi, dans le pire des cas, entraîner la formation de sous-produits toxiques. Il est donc important de savoir le plus précisément possible ce qui est dissous dans l’eau à traiter afin de rendre l’oxydation efficace. C’est là que la chercheuse Joanna Houska est intervenue, car jusqu’à présent, on utilisait principalement des paramètres globaux dérivés, par exemple, de l’absorption UV. Dans sa thèse, elle a donc tout d’abord développé des méthodes destinées à mesurer la concentration de composés pertinents. Elle les a ensuite caractérisés et a évalué s’ils pouvaient former des sous-produits problématiques, et dans quelle mesure. Enfin, elle a découvert, grâce aux isotopes de l’oxygène dans le peroxyde d’hydrogène, comment les précurseurs sensibles peuvent être distingués les uns des autres. Il est en outre intéressant de noter que Joanna Houska n’a pas limité sa recherche uniquement à la désinfection/l’oxydation de l’eau destinée à être utilisée comme eau potable. Bien plus, elle a également suivi, dans une station d’épuration, la formation de sous-produits de l’ozonation et leur dégradation ultérieure lors du traitement biologique secondaire des eaux usées épurées.

Pour la première fois en Suisse

Le Promotionspreis (en français: prix de thèse) dans le domaine de la chimie de l’eau est décerné depuis 1992 et est doté de 1500 euros. En 2024, il va pour la première fois à la Suisse. Joanna Houska sait déjà ce qu’elle fera de cet argent: «Mon vélo a besoin d’une mise à niveau urgente, donc l’argent du prix sera probablement investi là-dedans». Elle travaille désormais dans le département Environnement de Roche, dans le domaine des eaux usées et de la protection des eaux.
 

Photo de couverture: Joanna Houska lors de la remise du prix avec le Prof. Thomas Ternes au congrès annuel de la Wasserchemische Gesellschaft à Limburg (D) (Photo: Nina Hermes, BfG).
 

Publication originale

Oxidant-reactive carbonous moieties in dissolved organic matter: selective quantification by oxidative titration using chlorine dioxide and ozone

The application of oxidants for disinfection or micropollutant abatement during drinking water and wastewater treatment is accompanied by oxidation of matrix components such as dissolved organic matter (DOM). To improve predictions of the efficiency of oxidation processes and the formation of oxidation products, methods to determine concentrations of oxidant-reactive phenolic, olefinic or amine-type DOM moieties are critical.
Here, a novel selective oxidative titration approach is presented, which is based on reaction kinetics of oxidation reactions towards certain DOM moieties. Phenolic moieties were determined by oxidative titration with ClO2 and O3 for five DOM isolates and two secondary wastewater effluent samples. The determined concentrations of phenolic moieties correlated with the electron-donating capacity (EDC) and the formation of inorganic ClO2-byproducts (HOCl, ClO2−, ClO3−). ClO2-byproduct yields from phenol and DOM isolates and changes due to the application of molecular tagging for phenols revealed a better understanding of oxidant-reactive structures within DOM.
Overall, oxidative titrations with ClO2 and O3 provide a novel and promising tool to quantify oxidant-reactive moieties in complex mixtures such as DOM and can be expanded to other matrices or oxidants.
Houska, J.; Salhi, E.; Walpen, N.; von Gunten, U. (2021) Oxidant-reactive carbonous moieties in dissolved organic matter: selective quantification by oxidative titration using chlorine dioxide and ozone, Water Research, 207, 117790 (11 pp.), doi:10.1016/j.watres.2021.117790, Institutional Repository

Ozonation of lake water and wastewater: identification of carbonous and nitrogenous carbonyl-containing oxidation byproducts by non-target screening

Ozonation of drinking water and wastewater is accompanied by the formation of disinfection byproducts (DBPs) such as low molecular weight aldehydes and ketones from the reactions of ozone with dissolved organic matter (DOM). By applying a recently developed non-target workflow, 178 carbonous and nitrogenous carbonyl compounds were detected during bench-scale ozonation of two lake waters and three secondary wastewater effluent samples and full-scale ozonation of secondary treated wastewater effluent. An overlapping subset of carbonyl compounds (20%) was detected in all water types. Moreover, wastewater effluents showed a significantly higher fraction of N-containing carbonyl compounds (30%) compared to lake water (17%). All carbonyl compounds can be classified in 5 main formation trends as a function of increasing specific ozone doses. Formation trends upon ozonation and comparison of results in presence and absence of the •OH radical scavenger DMSO in combination with kinetic and mechanistic information allowed to elucidate potential carbonyl structures. A link between the detected carbonyl compounds and their precursors was established by ozonating six model compounds (phenol, 4-ethylphenol, 4-methoxyphenol, sorbic acid, 3-buten-2-ol and acetylacetone). About one third of the detected carbonous carbonyl compounds detected in real waters was also detected by ozonating model compounds.
Evaluation of the non-target analysis data revealed the identity of 15 carbonyl compounds, including hydroxylated aldehydes and ketones (e.g. hydroxyacetone, confidence level (CL) = 1), unsaturated dicarbonyls (e.g. acrolein, CL = 1; 2-butene-1,4-dial, CL = 1; 4-oxobut-2-enoic acid, CL = 2) and also a nitrogen-containing carbonyl compound (2-oxo-propanamide, CL =1).
Overall, this study shows the formation of versatile carbonous and nitrogenous carbonyl compounds upon ozonation involving ozone and •OH reactions. Carbonyl compounds with unknown toxicity might be formed, and it could be demonstrated that acrolein, malondialdehyde, methyl glyoxal, 2-butene-1,4-dial and 4-oxo-pentenal are degraded during biological post-treatment.
Houska, J.; Manasfi, T.; Gebhardt, I.; von Gunten, U. (2023) Ozonation of lake water and wastewater: identification of carbonous and nitrogenous carbonyl-containing oxidation byproducts by non-target screening, Water Research, 232, 119484 (17 pp.), doi:10.1016/j.watres.2022.119484, Institutional Repository

Hydrogen peroxide formation during ozonation of olefins and phenol: mechanistic insights from oxygen isotope signatures

Mitigation of undesired byproducts from ozonation of dissolved organic matter (DOM) such as aldehydes and ketones is currently hampered by limited knowledge of their precursors and formation pathways. Here, the stable oxygen isotope composition of H2O2 formed simultaneously with these byproducts was studied to determine if it can reveal this missing information. A newly developed procedure, which quantitatively transforms H2O2 to O2 for subsequent 18O/16O ratio analysis, was used to determine the δ18O of H2O2 generated from ozonated model compounds (olefins and phenol, pH 3-8). A constant enrichment of 18O in H2O2 with a δ18O value of ∼59‰ implies that 16O-16O bonds are cleaved preferentially in the intermediate Criegee ozonide, which is commonly formed from olefins. H2O2 from the ozonation of acrylic acid and phenol at pH 7 resulted in lower 18O enrichment (δ18O = 47-49‰). For acrylic acid, enhancement of one of the two pathways followed by a carbonyl-H2O2 equilibrium was responsible for the smaller δ18O of H2O2. During phenol ozonation at pH 7, various competing reactions leading to H2O2 via an intermediate ozone adduct are hypothesized to cause lower δ18O in H2O2. These insights provide a first step toward supporting pH-dependent H2O2 precursor elucidation in DOM.
Houska, J.; Stocco, L.; Hofstetter, T. B.; Gunten, U. von (2023) Hydrogen peroxide formation during ozonation of olefins and phenol: mechanistic insights from oxygen isotope signatures, Environmental Science and Technology, 57, 18950-18959, doi:10.1021/acs.est.3c00788, Institutional Repository

Formation of carbonyl compounds during ozonation of lake water and wastewater: development of a non-target screening method and quantification of target compounds

Ozonation of natural waters is typically associated with the formation of carbonyl compounds (aldehydes, ketones and ketoacids), a main class of organic disinfection byproducts (DBPs). However, the detection of carbonyl compounds in water and wastewater is challenged by multiple difficulties inherent to their physicochemical properties. A non-target screening method involving the derivatisation of carbonyl compounds with p-toluenesulfonylhydrazine (TSH) followed by their analysis using liquid chromatography coupled to electrospray ionisation high-resolution mass spectrometry (LC-ESI-HRMS) and an advanced non-target screening and data processing workflow was developed. The workflow was applied to investigate the formation of carbonyl compounds during ozonation of different water types including lake water, aqueous solutions containing Suwannee River Fulvic acid (SRFA), and wastewater. A higher sensitivity for most target carbonyl compounds was achieved compared to previous derivatisation methods. Moreover, the method allowed the identification of known and unknown carbonyl compounds. 8 out of 17 target carbonyl compounds were consistently detected above limits of quantification (LOQs) in most ozonated samples. Generally, the concentrations of the 8 detected target compounds decreased in the order: formaldehyde > acetaldehyde > glyoxylic acid > pyruvic acid > glutaraldehyde > 2,3-butanedione > glyoxal > 1-acetyl-1-cyclohexene. The DOC concentration-normalised formation of carbonyl compounds during ozonation was higher in wastewater and SRFA-containing water than in lake water. The specific ozone doses and the type of the dissolved organic matter (DOM) played a predominant role for the extent of formation of carbonyl compounds. Five formation trends were distinguished for different carbonyl compounds. Some compounds were produced continuously upon ozonation even at high ozone doses, while others reached a maximum concentration at a certain ozone dose above which they decreased. Concentrations of target and peak areas of non-target carbonyl compounds during full-scale ozonation at a wastewater treatment plant showed an increase as a function of the specific ozone dose (sum of 8 target compounds ∼ 280 µg/L at 1 mgO3/mgC), followed by a significant decrease after biological sand filtration (> 64-94% abatement for the different compounds). This highlights the biodegradability of target and non-target carbonyl compounds and the importance of biological post-treatment.
Manasfi, T.; Houska, J.; Gebhardt, I.; von Gunten, U. (2023) Formation of carbonyl compounds during ozonation of lake water and wastewater: development of a non-target screening method and quantification of target compounds, Water Research, 237, 119751 (14 pp.), doi:10.1016/j.watres.2023.119751, Institutional Repository

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