Analyse von Benzothiazolen und Untersuchungen zu deren Auftreten und mikrobiellem Abbau in aquatischen Proben

Abstract

The presented thesis is the first extensive study on the occurrence of benzothiazoles in municipal wastewater and their fate during biological treatment. Moreover street runoff, surface water and wastewater sludge were investigated. Samples were taken from municipal wastewater treatment plants in Ruhleben (Berlin, Germany) and GaoBeiDian (Beijing, China) and other locations in Berlin. An analytical method for the quantitative determination of six benzothiazoles, among them benzothiazole-2-sulfonic acid (BTSA) and 2-methylthiobenzothiazole (MTBT), from complex aqueous samples was developed. The method consists of analyte enrichment by solid phase extraction (SPE) and analysis by high pressure liquid chromatography (HPLC) combined with electrospray ionization tandem mass spectrometry (ESI-MS/MS). Detection limits of quantification in raw wastewater are in the range of 20-300 ng/L. External sample calibration is used to account for matrix effects and losses due to SPE. To minimize ionization suppression the flow into the ESI-source is reduced from 500 μL/min to below 100 μL/min by post-column splitting (PCS). The mean total concentration of benzothiazoles in municipal wastewater is generally around the 3 μg/L-range and exceeds in some instances 30 μg/L. BTSA dominates the composition followed by BT and OHBT. Conventional activated sludge (CAS) treatment could remove ABT, BT, OHBT and MBT (elimination > 40 %), but elimination of BTSA and MTBT was poor (below 25 %) and in some cases an increase in concentration (BTSA: +20 %, MTBT: +160 %) in the CAS treatment process was observed. Even by sophisticated membrane bioreactor (MBR) treatment the elimination of benzothiazoles was insufficient. Due to the incomplete elimination of benzothiazoles (below 35 % in total) these substances are discharged by municipal treatment plant effluents into the aquatic environment where they exhibit considerable long lifetimes. Emission sources for the release of benzothiazoles into municipal wastewater are largely unknown. Street runoff is shown to contain high concentrations of benzothiazoles (20-70 μg/L in total) but did not appear to be the decisive source for the occurrence of benzothiazoles in municipal wastewater. Positive findings of benzothiazoles in sanitary wastewater from private households confirm that private households are sources of emission. Yet there is no information on benzothiazoles used in households or in consumables. By investigating the microbial degradation of BT, OHBT and MBT by strains of Rhodococcus subspecies it could be demonstrated that their degradation follows the generally observed degradation pathway of aromatic compounds and prefers ortho-cleavage. Various metabolites from the degradation of BT, OHBT and MBT were identified using LC-ESI-MS/MS. However in samples of influent and effluent of a wastewater treatment plant these metabolites could not be detected. The presented work shows for the first time that considerable amounts of benzothiazoles are released into the environment by municipal treatment plant effluents. Especially polar BTSA plays an important role as it bears the potential to migrate into ground water aquifers. Former investigations systematically underestimated aquatic contamination with benzothiazoles as they did not detect BTSA.