Fate of Cr(III) during Ozonation of Secondary Municipal Wastewater Effluent |
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Authors: | Ioannis A Katsoyiannis Caroline Gachet Urs von Gunten |
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Affiliation: | 1. Department of Chemistry, Laboratory of Chemical and Environmental Technology, Aristotle University of Thessaloniki, Thessaloniki, Greece;2. School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerlandkatsogia@chem.auth.gr;4. School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland;5. Department of Water Resources and Drinking Water, Eawag, Swiss Federal Institute of Aquatic Science and Technology, Duebendorf, Switzerland |
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Abstract: | ABSTRACTIn the present study, the fate of trivalent chromium (Cr(III)) during ozonation of ultrapurified water and wastewater effluent was investigated. In experiments conducted in phosphate buffered ultrapurified water, O3 alone in excess was inefficient to oxidize Cr(III) (only about 10–15% of total Cr(III) content), while in presence of the secondary oxidant, OH radical, almost all Cr(III) was oxidized to hexavalent chromium (Cr(VI)). In a wastewater effluent, spiked with Cr(III), only about 10–20% of Cr(III) was oxidized with specific ozone doses in the range 0.15–1.5 gO3/gDOC, although O3 and OH radical were both available for reaction. Cr(VI) formation was monitored in parallel with the abatement of some common micropollutants, reacting with differing apparent second-order rate constants with ozone, decreasing in the order carbamazepine>> benzotriazole> atrazine> p-chlorobenzoic acid (pCBA). Carbamazepine and benzotriazole were abated to >80% for specific O3 doses of 0.3 gO3/gDOC and 0.8 gO3/gDOC, respectively. The more ozone-resistant compounds (atrazine and pCBA) required a specific ozone dose of about 1.25 gO3/gDOC for the same relative abatement. At this specific ozone dose (i.e., 1.25 gO3/gDOC), only about 20% of Cr(III) was oxidized to Cr(VI), whereas only 10% of Cr(III) was oxidized to Cr(VI) at a more realistic specific ozone dose for enhanced wastewater treatment for micropollutant abatement (0.5 gO3/gDOC). Therefore, for typical Cr(III) levels in municipal wastewaters, effluent ozonation only leads to toxicologically insignificant Cr(VI) concentrations. |
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Keywords: | Chromate Cr(Iii) Cr(Vi) Hydroxyl Radical Micropollutants Ozonation |
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