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pH-Dependent retention changes during membrane filtration of aluminum-coagulated solutions and the effect of precentrifugation.

Authors
  • Bérubé, Denis
  • Dorea, Caetano
Type
Published Article
Journal
Environmental Science & Technology
Publisher
American Chemical Society
Publication Date
Mar 19, 2013
Volume
47
Issue
6
Pages
2713–2720
Identifiers
DOI: 10.1021/es3027049
PMID: 23413878
Source
Medline
License
Unknown

Abstract

During jar tests on alum-based drinking water treatment, dissolved Al determinations on solutions coagulated at pH ≥ 6.5 were not reproducible. These determinations were performed by inductively coupled plasma mass spectrometry after syringe filtration (0.45 μm polyethersulfone membrane). In order to better define these anomalies, the filtrates were collected in sequential fractions of 7.5 mL. At coagulation pHs of 6.5 and 7.0, retention changes were demonstrated by large filtrate concentration reductions at all temperatures tested (0.1, 5.0, and 17.0 °C). In all cases, the concentrations converged to levels <50 μg/L within the fourth sequential fraction. In comparison, no retention change was observed for jar tests conducted at the same temperatures but in the low range of the minimum solubility domain, at pHs 5.5 and 6.0. The retention changes were also eliminated by precentrifugation (7000 g for 45 min; pH 6.5-7.2). At weaker precentrifugation conditions, as well as by varying membrane surface area or membrane fouling, the filtrate concentrations behaved according to a barrier buildup at the membrane-solution interface by unsettled flocculation residuals. The influence of flocculation time and temperature emphasized the importance of reaction rates, which could be enhanced at the interface by concentration polarization effects. These phenomena have implications on analytical protocols and on filtration in full-scale treatment.

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