Calcium Ion Mixing Modes Govern Membrane Fouling Mitigation During Membrane-Based Recovery of Extracellular Polymeric Substances
Recycling extracellular polymeric substances (EPSs) from excess sludge in wastewater treatment plants has garnered significant research attention. Membrane separation offers a promising approach for EPS concentration; however, membrane fouling remains a critical challenge. Previous studies demonstra...
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| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2025-06-01
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| Series: | Membranes |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2077-0375/15/6/169 |
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| Summary: | Recycling extracellular polymeric substances (EPSs) from excess sludge in wastewater treatment plants has garnered significant research attention. Membrane separation offers a promising approach for EPS concentration; however, membrane fouling remains a critical challenge. Previous studies demonstrate that Ca<sup>2+</sup> addition effectively mitigates membrane fouling. This study reveals that Ca<sup>2+</sup> mixing modes govern membrane fouling in the dead-end ultrafiltration of both the practical EPS and model EPS [sodium algiante (SA)]. The interaction mechanisms between Ca<sup>2</sup><sup>+</sup> and the EPS under varied mixing conditions and their impact on filtration performance were systematically investigated. At a low Ca<sup>2+</sup> concentration, the addition sequence critically influenced colloidal particle sizes formed via Ca<sup>2</sup><sup>+</sup>-EPS interactions, altering the cake layer structure governing filtration resistance; these effects diminished at higher Ca<sup>2+</sup> concentrations. In suspensions prepared by adding EPS to Ca<sup>2+</sup> solution (EPS-Ca), a portion of the EPS became encapsulated within an EPS-Ca layer formed through Ca<sup>2+</sup> EPS binding, reducing free EPS concentration and enlarging colloidal aggregates. This encapsulation reduced EPS-mediated membrane fouling, thereby lowering filtration resistance. Conversely, in suspensions prepared by adding Ca<sup>2+</sup> to EPS solution (Ca-EPS), more complete Ca<sup>2+</sup> EPS interactions formed a dense crosslinked structure with smaller colloids on membrane surfaces, intensifying fouling and resistance. Additionally, EPS-Ca exhibited higher compressibility than Ca-EPS, though both exhibited comparable filtration resistance under high-pressure conditions. These results offer critical insights into optimizing EPS ultrafiltration concentration to mitigate membrane fouling through Ca<sup>2+</sup> addition strategies. |
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| ISSN: | 2077-0375 |