Redox Behavior of Chromium in the Reduction, Coagulation, and Biotic Filtration (RCbF) Drinking Water Treatment

Mahringer, D., Ruhl, A. S., & Zerelli, S. S. (2023). Redox Behavior of Chromium in the Reduction, Coagulation, and Biotic Filtration (RCbF) Drinking Water Treatment. Water, 15 (2023), Heft 19. https://doi.org/10.60810/openumwelt-1375

Zusammenfassung englisch

The chromium (Cr) limit values are currently tightened to 25 (micro)g L-1 (EU), 5 (micro)g L-1 (Germany), and possibly 10 (micro)g L-1 Cr(VI) (California). The combined process of chemical reduction, coagulation, and biotic filtration (RCbF) efficiently removes Cr(VI) in drinking water. In this study, redox-active substances (O2, NO3-, Fe2+, MnO2) were investigated concerning their effect on the RCbF process. The experiments were performed at two-stage pilot waterworks for biological iron and manganese removal. O2 or NO3- as oxidants affected the RCbF process, neither by consumption of the reductant Fe(II) nor by re-oxidation of already formed Cr(III) in the supernatant of the filter bed. However, the oxidation of Cr(III) by O2 to Cr(VI) with MnO2 as a mediator was identified as potential risk for Cr breakthrough. Up to one third of the initial Cr(III) concentration was oxidized to Cr(VI) in the second filter bed within a contact time of only 5 min. The kinetically relevant mechanism seemed to be the formation of Cr(III)Fe(III)-hydroxides and not the reduction of Cr(VI) by Fe(II). Further, the mixing of Cr(VI) containing raw water with Fe(II) containing groundwater was determined as a chemical-free alternative for the RCbF process, depending on the resulting Fe(II) concentration after mixing. © 2023 by the authors

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https://openumwelt.de/handle/123456789/1667

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