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Joanna Houska at the award ceremony with Prof. Thomas Ternes, at the Annual Meeting of the German Water Chemistry Society in Limburg (photo: Nina Hermes, BfG).

Prize-winning thesis: oxidation done properly!

July 17, 2024 | Andri Bryner

Environmental chemist Joanna Houska has received an award for her doctoral thesis from the German Water Chemistry Society. She conducted her research at Eawag and EPFL, demonstrating both theoretically and experimentally how oxidative water treatment using ozone or chlorine can be more efficiently utilized when there is a precise understanding of the organic substances dissolved in the water to be treated.

"This work is a milestone along the road to advancing our understanding of the role of dissolved organic matter in oxidative water treatment," stated Joanna Houska's supervisor, Urs von Gunten, who is a professor at EPFL and head of the Drinking Water Chemistry Group at Eawag. According to von Gunten, Houska possesses "a remarkable ability to tackle complex scientific questions both theoretically and experimentally, successfully resolving issues with great independence.” Her experiments and modelling have produced and interpreted exciting new data, offering insights that can be employed to improve oxidative water treatment methods.

Inefficient and hazardous without accurate analysis

What is the underlying issue? When chlorine or ozone are used for water disinfection/oxidation, the primary goal is to render pathogens and micro-pollutants harmless. However, a substantial proportion of the oxidants reacts with water matrix components such as dissolved organic materials. This not only reduces the efficiency of the treatment process, but, in the worst-case scenario, can also lead to the formation of toxic by-products. For efficient oxidation, it is therefore crucial to have a precise understanding of the dissolved substances in the water being treated. Traditional approaches have hitherto relied mainly on aggregate parameters derived, for example, from UV absorption. However, Houska addressed this gap in her thesis, firstly developing methods to measure the concentrations of relevant compounds, and then characterising and evaluating the compounds as to whether and to what extent they could form problematic by-products. Lastly, she revealed insights into oxygen isotopes in hydrogen peroxide, demonstrating how the problematic precursor substances can be distinguished from one another. Notably, in her research, Houska went beyond the disinfection/oxidation of drinking water to also investigate the formation of ozone by-products at a wastewater treatment plant and their subsequent degradation in biological post-treatment of treated wastewater.

A first for Switzerland

The doctoral prize in the field of water chemistry has been awarded every year since 1992, and carries with it EUR 1,500. 2024 sees it being awarded for the first time in Switzerland. Joanna Houska already knows how she will use the prize money: "My bicycle urgently needs an upgrade, so the prize money will likely be invested in that.” She currently works in the environmental department at Roche, in the area of wastewater and water protection.
 

Cover picture: Joanna Houska at the award ceremony with Prof. Thomas Ternes, at the Annual Meeting of the German Water Chemistry Society in Limburg (photo: Nina Hermes, BfG).
 

Original publication

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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