Department Environmental Toxicology

Advanced oxidation processes

Treatment of water by oxidation processes – Testing schemes for assessment of toxicity 

A number of technical and natural processes leads to the transformation of chemicals in the aquatic environment. These processes include ozonation and ultraviolet radiation. Even otherwise stable chemicals can be eliminated in this, for example from drinking and waste water. Is, however, the transformation of the chemicals identical to a reduced environmental risk? Based on a tight link between understanding chemical transformation processes, chemical analytics and biological assays, we develop strategies that allow to address this question. The so-called effect-driven assessment is at the heart of this procedure. 

The effect-driven assessment approach is based on the toxic potential of the parent compound and of the mixtures arising from transformation processes, as determined by biological testing. If, during transformation, the toxic potential of a mixture decreases in proportion to the disappearance of the parent compound, it can be assumed that toxicity is dominated by the parent compound, and the transformation products are not relevant for the environmental risk assessment. Only if the toxicity of the mixture is greater than would be expected for the parent compound are further steps required to identify the toxicologically active substance(s) (Figure 1). This would include, for example, a combination of fractionation and biological and chemical analysis. We have so far explored this strategy for a number of different chemical classes and biological effects in defined water samples as well as complex matrices.

Publications

Advanced oxidation and transformation of organic contaminants

Objectives
The goal of the project was to evaluate the treatment of a representative list of organic contaminants from the Contaminant Candidate List 3 (CCL 3) via UV- and ozone-based advanced oxidation processes (AOPs). The research focused on these chemicals because they are being explored for possible regulation by the EPA in the future. The specific objectives of the research were to:
1. Select and prioritize CCL3 contaminants for investigation
2. Select bioassays used to evaluate biological activity
3. Apply advanced oxidation treatment of CCL3 chemicals using UV-H2O2 and O3/O3-H2O2 processes
4. Monitor AOP treatment using bioassay testing
5. Engineer evaluation for AOP operating conditions that minimize post-treatment bioactivity [...]
Linden, K. G.; Parker, A. M.; Rosario-Ortiz, F.; von Gunten, U.; Mestankova, H.; Canonica, S.; Schirmer, K.; Cotton, C.; Collins, J.; Elovitz, M.; Swaim, P. (2015) Advanced oxidation and transformation of organic contaminants, 130 p, Institutional Repository

Novel test procedure to evaluate the treatability of wastewater with ozone

Organic micropollutants such as pharmaceuticals, estrogens or pesticides enter the environment continuously through the effluent of municipal wastewater treatment plants (WWTPs). Enhanced treatment of wastewater (WW) by ozone (O3) is probably one of the simplest measures for abatement of organic micropollutants to avoid their discharge to the aquatic environment. During ozonation most organic micropollutants present in treated WW are oxidized either by a direct reaction with O3 or by secondarily formed hydroxyl radicals (·OH). However, undesired oxidation by-products from the oxidative transformation of matrix components can also be formed. A modular laboratory decision tool based on the findings of previous investigations is presented to test the feasibility of ozonation as an option to upgrade specific WWTPs. These modules consist of investigations to assess (i) the matrix effects on ozone stability, (ii) the efficiency of micropollutant removal, (iii) the oxidation by-product formation, as well as (iv) bioassays to measure specific and unspecific toxicity of the treated WWs.
Matrix effects on ozone stability (quantified as O3 and ·OH exposures) can give first indications on the suitability of an ozonation step. Ozonation of WWs yielding O3 and ·OH exposures and micropollutant abatement similar to reference values evoked a significant improvement of the water quality as indicated by a broad range of bioassays. Irregular behavior of the ozonation points towards unknown compounds, possibly leading to the formation of undesired degradation products. It has been observed that in such WWs ozonation partly enhanced toxicity. In summary, the presented tiered laboratory test procedure represents a relatively cheap and straight-forward methodology to evaluate the feasibility of ozonation to upgrade specific WWTPs for micropollutant removal based on chemical and biological measurements.
Schindler Wildhaber, Y.; Mestankova, H.; Schärer, M.; Schirmer, K.; Salhi, E.; von Gunten, U. (2015) Novel test procedure to evaluate the treatability of wastewater with ozone, Water Research, 75, 324-335, doi:10.1016/j.watres.2015.02.030, Institutional Repository

Behandelbarkeit von Abwasser mit Ozon. Testverfahren zur Beurteilung

Eine Ozonung als zusätzliche Reinigungsstufe auf einer kommunalen Abwasserreinigungsanlage (ARA) bewirkt eine deutliche Abnahme der Mikroverunreinigungen. Bei speziellen Belastungen, z.B. aufgrund bedeutender Industrie- oder Gewerbeabwassereinleitungen, können durch die Ozonung jedoch neue Stoffe, sogenannte Transformationsprodukte, gebildet werden. Daher soll künftig im Einzelfall ein Testverfahren aus fünf Modulen prüfen, ob sich ein bestimmtes Abwasser für eine Ozonbehandlung eignet oder nicht.
Wunderlin, P.; Mestankova, H.; Salhi, E.; Schindler Wildhaber, Y.; Schärer, M.; Schirmer, K.; von Gunten, U. (2015) Behandelbarkeit von Abwasser mit Ozon. Testverfahren zur Beurteilung, Aqua & Gas, 95(7-8), 28-38, Institutional Repository

Development of mutagenicity during degradation of N-nitrosamines by advanced oxidation processes

Development of mutagenicity of five N-nitrosamines (N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), N-nitrosodi-n-propylamine (NDPA), N-nitrosopyrrolidine (NPYR) and N-nitrosodiphenylamine (NDPhA)) was investigated during oxidative processes involving UV-photolysis, ozone and ·OH radicals. The mutagenicity was detected by the Ames test with 3 different strains, TA98, TAMix and YG7108, a strain which is sensitive for N-nitrosamines, in presence and absence of metabolic activation (S9). UV photolysis of mutagenic N-nitrosamines (NDMA, NDEA, NDPA and NPYR) leads to the removal of their specific mutagenic activity as detected in YG7108 in the presence of S9. A formation of mutagens during UV photolysis was detected only in case of NDPhA in the strain TA98. Oxidation products of NDMA, NDEA and NDPhA did not show any significant mutagenicity in the strains used, whereas oxidation of NDPA and NPYR by hydroxyl radicals seems to lead to the formation of direct mutagens (mutagenic in the absence of S9) in YG7108 and TAMix. Oxidation by hydroxyl radicals of N-nitrosamines with chains longer than ethyl can mimic metabolic activation of N-nitrosamines in vivo.
Mestankova, H.; Schirmer, K.; Canonica, S.; von Gunten, U. (2014) Development of mutagenicity during degradation of N-nitrosamines by advanced oxidation processes, Water Research, 66, 399-410, doi:10.1016/j.watres.2014.08.012, Institutional Repository

Removal of the antiviral agent oseltamivir and its biological activity by oxidative processes

The antiviral agent oseltamivir acid (OA, the active metabolite of Tamiflu®) may occur at high concentrations in wastewater during pandemic influenza events. To eliminate OA and its antiviral activity from wastewater, ozonation and advanced oxidation processes were investigated. For circumneutral pH, kinetic measurements yielded second-order rate constants of 1.7 ± 0.1 × 105 and 4.7 ± 0.2 × 109 M−1 s−1 for the reaction of OA with ozone and hydroxyl radical, respectively. During the degradation of OA by both oxidants, the antiviral activity of the treated aqueous solutions was measured by inhibition of neuraminidase activity of two different viral strains. A transient, moderate (two-fold) increase in antiviral activity was observed in solutions treated up to a level of 50% OA transformation, while for higher degrees of transformation the activity corresponded to that caused exclusively by OA. OA was efficiently removed by ozonation in a wastewater treatment plant effluent, suggesting that ozonation can be applied to remove OA from wastewater.
Mestankova, H.; Schirmer, K.; Escher, B. I.; von Gunten, U.; Canonica, S. (2012) Removal of the antiviral agent oseltamivir and its biological activity by oxidative processes, Environmental Pollution, 161, 30-35, doi:10.1016/j.envpol.2011.09.018, Institutional Repository