Chromium removal in the presence of NOM during Fe(II) reductive precipitation for drinking water treatment
Langer, Margarethe and Jamal, Mohammad Umair and Conklin, Amanda and Ernst, Mathias (2022) Chromium removal in the presence of NOM during Fe(II) reductive precipitation for drinking water treatment. Water, 14 (18). 2903. ISSN 2073-4441 (https://doi.org/10.3390/w14182903)
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Abstract
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.
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Item type: Article ID code: 90289 Dates: DateEvent16 September 2022Published14 September 2022AcceptedSubjects: Technology > Environmental technology. Sanitary engineering
Technology > Chemical engineeringDepartment: Faculty of Engineering > Chemical and Process Engineering Depositing user: Pure Administrator Date deposited: 19 Aug 2024 11:49 Last modified: 03 Oct 2024 09:24 URI: https://strathprints.strath.ac.uk/id/eprint/90289