Synergistic fouling behaviors and mechanisms of calcium ions and polyaluminum chloride associated with alginate solution in coagulation-ultrafiltration (UF) process. (1st February 2021)

• Record Type: Journal Article
• Authors: Long, Ying; Yu, Genying; Dong, Lu; Xu, Yanchao; Lin, Hongjun; Deng, Ying; You, Xiujia; Yang, Lining; Liao, Biao-Qiang
• Is Part Of: Water research. Volume 189(2021)
• Publication Date: 2021-02-01
• Subjects: Membrane fouling -- Calcium ion -- Coagulation-ultrafiltration process -- Synergistic effects -- Thermodynamic mechanisms; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2020.116665
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: alginate specific filtration resistance (SFR) had a unimodal trend with Al 3+ or Ca 2+ addition alone. Ca 2+ and Al 3+ had synergistic effects to reduce alginate SFR and fouling. initial binding Ca 2+ and Al 3+ ions to alginates formed special geometries, increasing SFR. Ca 2+ and Al 3+ sequentially elongated gel network and clustered compounds, reducing SFR. the newly proposed thermodynamic mechanisms allowed to optimize coagulation-UF process. Abstract: Effects of calcium ions and polyaluminum chloride (PACl) on membrane fouling in coagulation-ultrafiltration (UF) process were investigated in this study. Filtration tests demonstrated three interesting filtration behaviors: 1) high specific filtration resistance (SFR) of alginate solution with low CaCl2 or PACl addition (e. g. 3.51×10 15 m· kg -1 under the condition of 1.5 mM CaCl2 addition); 2) unimodal pattern of alginate SFR with PACl or CaCl2 addition alone; 3) synergistic effects between CaCl2 and PACl on alginate SFR. It was found that, the foulant morphological changes driven by the thermodynamic mechanisms based on Flory-Huggins lattice theory take the critical roles in these filtration behaviors. Density functional theory (DFT) calculations showed that initial coordination of Ca 2+ and Al 3+ ions with alginates tended to form tetrahedron geometry and geometry of coordinating three terminal carboxyl groups, respectively, which facilitated to elongate the alginate chains (without clustering the flocs) and form more stable gel, increasing SFR. Improving Ca 2+ and Al 3+ dosages triggered transition to other geometries for clustering polymeric network and flocculation, reducing SFR. Due to the higher binding affinity of Ca 2+ over Al 3+, Ca 2+ and Al 3+ sequentially take roles of enlarging polymeric network and clustering the coordination compounds, and then facilitate to form large size flocs and reduce SFR, causing the synergistic effects between CaCl2 and PACl additions. The proposed thermodynamic mechanisms satisfactorily explained these interesting fouling behaviors, allowing to further optimize coagulation-UF process. Graphical abstract: Image, graphical abstract