Removal of Chromium Species from Low-Contaminated Raw Water by Different Drinking Water Treatment Processes
Author:
Konradt Norbert1ORCID, Dillmann Saskia2, Becker Jennifer3, Schroden Detlef1, Rohns Hans-Peter1, Wagner Christoph1, Müller Uwe4, Konradt Daniel5, Janknecht Peter6, Hobby Ralph7, ElSherbiny Ibrahim M. A.7ORCID, Panglisch Stefan789ORCID
Affiliation:
1. Department of Waterworks, Stadtwerke Düsseldorf AG, Wiedfeld 50, 40589 Düsseldorf, Germany 2. BEW—Das Bildungszentrum für die Ver—und Entsorgungswirtschaft gGmbH, Dr.-Detlev-Karsten-Rohwedder-Straße 70, 47228 Duisburg, Germany 3. Inwatec GmbH & Co. KG, Römerstraße 131, 50127 Bergheim, Germany 4. TZW: DVGW Technologiezentrum Wasser, Karlsruher Straße 84, 76139 Karlsruhe, Germany 5. Faculty of Mechanical Engineering, Ruhr University Bochum, Universitätsstraße 150, 44801 Bochum, Germany 6. Enercity AG, Ihmeplatz 2, 30449 Hannover, Germany 7. Chair for Mechanical Process Engineering and Water Technology, University of Duisburg-Essen, 47057 Duisburg, Germany 8. IWW Water Center, Moritzstraße 26, 45476 Mülheim an der Ruhr, Germany 9. Centre for Water and Environmental Research (ZWU), Universitätsstraße 2, 45141 Essen, Germany
Abstract
The occurrence of Cr (VI) in drinking water resources in low but toxicologically relevant concentrations requires the development of reliable and industrially applicable separation processes in drinking water treatment. There is little information in the literature on the removal of chromium species at concentrations below 10 µg/L. Therefore, in this study, the removal of chromium in the concentration range ≤10 µg/L was investigated using three separation processes, activated carbon filtration (ACF), reduction/coagulation/filtration (RCF) and low-pressure reverse osmosis (LPRO), in both laboratory- and pilot-scale tests. In ACF treatment, Cr (III) was removed by deep bed filtration over 1.5 m of anthracite at a pH of 7.5 (which was used as a prefilter prior to ACF), while Cr (VI) was removed up to 75% via ACF at a filter bed depth of 2.5 m. Fresh activated carbon (AC) exhibited the highest adsorption capacity for Cr (VI), while reactivated AC had a significantly lower capacity for Cr (VI), which was attributed to calcium and iron deposits. In technical filters, where multiple reactivated activated carbon is used, this led to a low removal rate for Cr (VI). Using the RCF process with Fe (II) dosing in a continuous flow reactor at a specific coagulant dosing ratio, high Cr (VI) removal, down to a concentration of 0.1 µg/L, was achieved within minutes. The subsequent anthracite filtration ensured the complete removal of Fe (III) and Cr (III) precipitates. The RCF process was limited by the oxygen side reaction with Fe (II), which dominated at Cr (VI) concentrations below 1 µg/L. In addition, a four-step LPRO process with concentrate recycling showed effective removal (>99%) of both Cr (III) and Cr (VI) species in raw water as well as a negligible effect of pH in the testing pH range of 5.6 to 8.3 on the Cr (VI) removal. Nevertheless, the water hardness and pH of the LPRO permeate must be increased to make it available as drinking water. The three separation processes were found to be able to meet the expected more stringent future regulations for Cr (VI) level in drinking water. The most suitable technology, however, can be selected with respect to the raw water quality/characteristics, site-specific conditions and the already existing equipment.
Subject
Water Science and Technology,Aquatic Science,Geography, Planning and Development,Biochemistry
Reference51 articles.
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