Insights into the roles of recently developed coagulants as pretreatment to remove effluent organic matter for membrane fouling mitigation

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Journal Article
Journal of Membrane Science, 2018, 564 pp. 643 - 652
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20180719 Ly et al (manuscript)-Revised JMS.pdfAccepted Manuscript Version1.33 MB
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© 2018 Elsevier B.V. Membrane fouling by dissolved organic matter (EfOM) in secondary treated effluent is a problematic and inevitable issue during wastewater reclamation using low pressure membrane filtration. This study evaluates the performance of coagulation/flocculation (C/F) using two recently developed coagulants (namely TiCl 4 and ZrCl 4 ) in comparison to conventional alum (i.e. Al 2 (SO 4 ) 3 ) as pretreatment to remove EfOM for subsequent ultrafiltration (UF) membrane fouling mitigation. At the optimal dosage, TiCl 4 -based C/F pretreatment showed the greatest performance in membrane fouling mitigation, followed by ZrCl 4 and then alum. The underlying mechanisms were well explained by classical fouling models and the extended Derjaguin-Landau-Verwey-Overbeek (xDLVO) theory, highlighting a dominant role of standard blocking in the fouling potential of the C/F treated EfOM. The interfacial free energy of cohesion and adhesion showed that C/F pretreatment using TiCl 4 and ZrCl 4 as coagulant can lower the binding affinity between EfOM molecules and between EfOM molecules and membrane surface, ultimately reduce membrane fouling. The results of size exclusion chromatography (SEC) and fluorescence excitation emission matrix- parallel factor analysis (EEM-PARAFAC) also supported the classical fouling mechanisms, providing additional insights into the potential roles of chemical interactions in the preferential removal of certain organic substances by C/F pretreatment and the chemical composition of subsequent membrane foulants. Protein-like components were highly associated with reversible fouling after the C/F, while the reversibility of humic-like substances was enhanced upon C/F pretreatment. After C/F pretreatment, small sized EfOM molecules became the dominant fraction responsible for UF membrane fouling.
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