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Article

Chromium Removal in the Presence of NOM during Fe(II) Reductive Precipitation for Drinking Water Treatment

1
Institute for Water Resources and Water Supply, Technische Universität Hamburg, Am Schwarzenberg-Campus 3, 21073 Hamburg, Germany
2
Department of Chemical and Process Engineering, University of Strathclyde, 75 Montrose Street, Glasgow G1 1XL, UK
3
Indian Health Services, Office of Environmental Health and Engineering, 557 W Silver Street, Elko, NV 89801, USA
*
Authors to whom correspondence should be addressed.
Academic Editor: Zhiliang Zhu
Water 2022, 14(18), 2903; https://doi.org/10.3390/w14182903
Received: 24 July 2022 / Revised: 10 September 2022 / Accepted: 14 September 2022 / Published: 16 September 2022
(This article belongs to the Section Wastewater Treatment and Reuse)
Cr(VI) is toxic and carcinogenic, which fuels discussions on reducing existing standards for maximum Cr concentrations in drinking water. Fe(II) reductive precipitation is a common and economical method for achieving very low Cr(tot) concentrations (<5 µg/L). While Cr(VI) is reduced to Cr(III), Fe(II) is oxidized to Fe(III). The resulting Cr(III) and Fe(III) have low solubilities at neutral pH, precipitate as hydroxides, and can be removed by conventional media filtration. The presence of natural organic matter (NOM) in the raw water source can, depending on pH, concentration, type of NOM, and contact time, affect this process in various ways, from promoting Cr(VI) reduction, to re-reducing Fe(III), to forming stable complexes with Cr and Fe, thus, impairing chromium removal. The presented data showed that NOM, whether dominated by terrestrial humic acid, or of aquatic origin, could substantially impair chromium removal at neutral pH conditions. In particular, the ultimate removal of Cr(III) was affected. Soluble complexes and/or colloids of Cr(III), Fe(III) and NOM in the size range of 10 kDa–0.1 µm were formed, that could not be removed by conventional media filtration. Presence of iron sludge (>50 mg/L Fe(III)) mitigated the negative impacts of NOM on Cr(VI) reduction and Cr(III) removal. However, even 100 mg/L Fe(III), the highest applied sludge concentration, did not lead to a decrease in Fe(II) dosing requirements under the given conditions. A molar ratio higher than the given stochiometric ratio of [Fe(II)]:[Cr(VI)] = 3 was necessary for sufficient Cr(VI) removal. View Full-Text
Keywords: chromium removal; Fe(II); reductive precipitation; humic acid; NOM; drinking water chromium removal; Fe(II); reductive precipitation; humic acid; NOM; drinking water
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MDPI and ACS Style

Langer, M.; Jamal, M.U.; Conklin, A.; Ernst, M. Chromium Removal in the Presence of NOM during Fe(II) Reductive Precipitation for Drinking Water Treatment. Water 2022, 14, 2903. https://doi.org/10.3390/w14182903

AMA Style

Langer M, Jamal MU, Conklin A, Ernst M. Chromium Removal in the Presence of NOM during Fe(II) Reductive Precipitation for Drinking Water Treatment. Water. 2022; 14(18):2903. https://doi.org/10.3390/w14182903

Chicago/Turabian Style

Langer, Margarethe, Mohammad Umair Jamal, Amanda Conklin, and Mathias Ernst. 2022. "Chromium Removal in the Presence of NOM during Fe(II) Reductive Precipitation for Drinking Water Treatment" Water 14, no. 18: 2903. https://doi.org/10.3390/w14182903

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