Wastewater effluents are a major point source of contaminants in aquatic ecosystems as wastewater treatment plants emit a plethora of so-called micropollutants. These are chemicals (e.g., pharmaceuticals) that are insufficiently removed during conventional, activated sludge treatment and, therefore, released into the receiving water body. Here, low concentration complex mixtures of micropollutants contribute to the degradation of freshwater biodiversity.

To address this issue, environmental engineers have developed so-called advanced wastewater treatment technologies. In principle, these are to be implemented after the biological treatment and are either based on adsorption (e.g., activated carbon) or oxidation (e.g., ozonation). When looking at specific, target chemicals, advanced treatment is very effective in further reducing the load of micropollutants.

However, as we realize that the chemicals we monitor contribute – if at all – only to a minor extent to the toxicological effects observed in the environment (“tip of the iceberg”), we miss an important piece of the puzzle. Accordingly, we use in vitro and in vivo bioassays to evaluate the removal of toxicity by conventional and advanced wastewater treatment. In combination with chemical analysis, this will generate a more holistic picture of the presence and and potential mitigation of chemical stressors in the aquatic environment.

In a range of projects, we have evaluated the performance of (advanced) wastewater treatment to remove toxicity: In the project EU project NEPTUNE, we demonstrated that ozonation generates transformation products that induce in vivo toxicity. In TransRisk and SchussenAktivplus, we have investigated different combinations of ozonation, activated carbon treatment and biofiltration to increase the efficiency of treatment.

In our research, we apply sensitive in vitro bioassays for specific mechanisms of action (receptor-mediated, DNA damage etc.) as well as unspecific toxicity (cytotoxicity, oxidative stress etc.). We further perform chronic toxicity studies with aquatic plants (Lemna minor, Scenedesmus subspicatus) and invertebrates (Caenorhabditis elegans, Chironomus riparius, Daphnia magna, Gammarus pulex, Lumbriculus variegatus, Potamopyrgus antipodarum etc.) on a lab scale or in on-site, flow-through systems installed directly at different wastewater treatment plants.

Based on this empirical data, we develop concepts on how to integrate chemical, in vitro and in vivo information to assess the performance of wastewater treatment. We use our knowledge to collaborate with engineers and chemists in further improving wastewater treatment technologies. One great example is the ERC project ATHENE, in which we have recently shown that an optimized biological treatment has a hidden potential for toxicity removal.