Ozone (O3) with its high oxidation potential was used to degrade or eliminate pollutants contained in tannery wastewater when applying different pHs and quantities of O3. Our objective was a chemical degradation by O3 to achieve an enhancement of biodegradability, with a parallel decrease in toxicity. Conventional analyses and bioassays beside substance specific analyses were performed to clear-up the behaviour of wastewater content from tanning process. The results demonstrate that the dominant organic pollutants were chemically degraded by oxidation as the chemical and biochemical oxygen demand (COD and BOD) prove, while changes in carbon content monitored by total or dissolved organic carbon content (TOC or DOC) were only marginal. Vibrio fischeri and Daphnia magna toxicity testing performed in parallel proved a decrease in toxicity after O3-treatment, while the estrogenic activity determined by enzyme-linked receptor assay (ELRA), however, proved an increase of endocrine disruptor compounds (EDC). Results could be explained by substance-specific analyses using gas chromatography (GC-MS) and liquid chromatography/mass spectrometry (LC-MS). From GC-MS analysis the elimination of non-polar compounds could be recognized, whereas the oxidative conversion led to an increase of EDC compounds, which qualitatively could be identified by LC-MS as nonylphenol ethoxylate (NPEO) degradation products: short chain NPEOs, nonylphenol carboxylates (NPECs) and nonylphenol (NP).

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