Ozonation is increasingly applied in water and wastewater treatment for an abatement of micropollutants. However, the transformation products formed during ozonation (OTPs) and their fate in biological post-treatment are largely unknown. In this project, OTPs are identified from a mixture of a large number of exposure-relevant micropollutants with lab scale experiments in differing simulated water matrices. The relevance of the so identified OTPs is examined by checking their abundance in ambient water after pilot-scale and full-scale ozonation. Furthermore, the fate of OTPs is studied in biological post-treatment of ozonated drinking water and wastewater to get a mechanistic understanding of their biodegradability and to identify persistent and water-relevant OTPs. This collaboration with the Wasserversorgung Zürich provides a strong link to the drinking water community in Switzerland and beyond.