Occurrence of polycyclic aromatic hydrocarbons in surface water and hospital wastewater

The main objective of this study was to determine the occurrence of polycyclic aromatic hydrocarbons (PAHs) in surface water samples collected from different points along the stream that flows through the Campus of the Federal University of Santa Maria, RS-Brazil. Before reaching the campus, the water in the stream is already contaminated by wastewater discharged from the surrounding, and once inside the Campus, additional wastewater from a Gas Station situated close to the University hospital. A bench scale photodegradation experiment was conducted of the occurring traces of anthracene, phenanthrene and naphthalene, with the aid of a stirred tank reactor and polymer-supported TiO₂ as a catalyst. To prevent loss of the low soluble analytes, it was necessary to add 5% and 10% acetonitrile, as an organic modifier of the synthetic aqueous solutions and real samples, respectively. An experimental design was employed and the best conditions for the photocatalysis of the aqueous solutions and real samples were pH 9 and pH 7, and 35°C and 30°C, respectively. Under optimized conditions, the analytes were completely degraded after 60 min of irradiation. The subproducts of the photocatalysis were identified through gas chromatography/mass spectrometry, and fragmentation routes were proposed. The mean concentrations of PAHs in the polluted surface water and hospital wastewater were relatively high: 3.9 ± 1.7 and 21.5 ± 2.8 µg L^-1, respectively. A preliminary risk assessment revealed that the presence of anthracene requires particular attention. The risk posed by the occurrence of PAHs in the surface water and hospital wastewater samples confirms the need for an efficient treatment system.