Functional group specific reactivity, transformation and persistence of CECs and EfOM during wastewater ozonation

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Chemical oxidation by ozone is an established technology for the efficient oxidation of contaminants of emerging concern (CEC) in water treatment. A major disadvantage of using ozone is the formation of stable and potentially toxic ozonation products (OPs). Biologically stable OPs are particularly critical due to their longevity in the environment. It is impossible to examine all relevant CECs for their reactivity towards ozone, the resulting OPs and their biological stability. Rather, it is necessary to generate knowledge based on the systematic study of functional groups that can be transferred to other substances. So far, such systematic studies have not been carried out. The knowledge gap for effluent organic matter (EfOM) is even larger. The ozone consumption of EfOM proves its reactivity to ozone, but which functional groups react, which products are formed and how biologically stable they are, has not been investigated for EfOM especially with heteroatoms (N, S).This project aims to fill both gaps by a complementary analytical and experimental approach, with the common methodological approach of introducing a label into the OPs by using 18O-ozone and the subsequent detection and identification of the OPs by means of (ultra-high-resolution) mass spectrometry.The project is based on the central hypothesis that the reaction of ozone with certain functional groups of CECs as well as with equivalent functional groups of the EfOM leads to a predictable formation of OPs. It aims to i) improve our understanding of the reactivity of different functional groups to ozone, focusing on the identification of non-biodegradable functional groups within the OPs, ii) identify and quantify ozone-reactive functional groups in the EfOM based on existing knowledge on the transformation of CECs, with the focus on N- and S-containing functional groups which form potentially chemically stable OPs, and iii) assess the significance of the EfOM with respect to the formation of biologically stable OPs in wastewater ozonation in comparison to CECs.To that end, the biological degradation of the OPs will be investigated using their specific functional groups in column degradation experiments and managed aquifer recharge studies. With the new labeling approach, we are able to reliably detect CEC and EfOM OPs, identify them and track their stability in biological systems.The project generates a systematic and transferable understanding of the formation of stable OPs based on functional groups of organic molecules, both of CECs and EfOM. Only when the stability of the possible OPs has been investigated a systematic toxicological evaluation of ozonation as a water treatment method will become feasible.