Titel der Dissertation: Biological transformation of pharmaceuticals and the occurrence of transformation products in the water cycle

An increasing life expectancy and medical advances are intensifying the demand for, and emission of, pharmaceuticals detected at concentrations ranging from pg L-1 to μg L-1 in surface water, groundwater and potable water. Once pharmaceuticals are introduced into wastewater treatment plants (WWTPs), they can be converted to transformation products (TPs) which are potentially more harmful. Furthermore, pharmaceuticals are designed to be biologically active, which is why they and their TPs can affect humans and organisms even at low concentrations. For example, antibiotic resistant bacterial strains are a threat to human health and antibiotics released into the environment have a potential to promote this resistance. Nevertheless, there is still a better understanding about the overall fate of pharmaceuticals and occurrence in the water cycle needed. The transformation studies with four pharmaceuticals and corresponding monitoring campaigns conducted in this dissertation advance that goal and are aimed to support environmental risk assessment of chemicals released into the environment.

The chosen compounds include gabapentin (GBP) and pregabalin (PGB), two structurally related anticonvulsants ubiquitously detected in surface waters. Lab-scale incubation experiments using water/sediment systems revealed very similar behaviour for both compounds regarding their transformation kinetics and pathways. This led to the conclusion that the transformation behaviour of GBP can be largely extrapolated to PGB due to the functional groups they have in common. These findings can help to improve pathway prediction systems applied within the risk assessment of chemicals. Furthermore, the findings point out that although PGB and GBP were degraded to 20 TPs during incubation, monitoring studies prove that the self-regulating capacity of the environment and conventional WWTPs is not sufficient, as GBP, PGB and up to five TPs can reach German bank filtrates and potable water.

Therefore, another particular focus during this thesis was placed on advanced biological processes, in particular moving bed biofilm reactors (MBBR) for an improved removal of pharmaceuticals from wastewater. Knowledge about the fate of the antidiabetic sitagliptin (STG) and antihistaminic fexofenadine (FXF) commonly found in WWTPs is rare, which lead to investigations regarding their behaviour in contact with suspended and attached biomass used in activated sludge processes and MBBRs, respectively. Lab-scale incubations revealed that in comparison to suspended biomass, the attached biomass accelerated the oxidative transformation of FXF but slowed the hydrolytic transformation of STG. These observations serve as a starting point for further studies (e.g. multi-compound studies and metatranscriptome analysis), investigating if the composition of microbial communities differ in various biomass shapes and can therefore favour specific enzymatic reactions.