Investigations of antifouling properties of modified ultrafiltration membrane materials for drinking water treatment
Within the framework of MABMEM research project, newly developed polyether sulfone (PESU)-based and polyphenylene sulfone (PPSU)-based single bore hollow fiber UF membranes were evaluated in comparative and standardized fouling tests. To realize a reliable decision-making process regarding promising membrane candidates within a reasonable experiment time, it was crucial to design lab-scale filtration experiments as close as possible to real-scale UF plants. Most of literature reporting on performance of ultrafiltration membranes were performed in bench-scale experiments employing flat-sheets at operating conditions far from what is seen in real-scale applications. Moreover, the employed feed solutions were mostly made from real natural resources, where maintaining their quality over long testing periods is often a challenge. In addition, the ability of extensively reported synthetic fouling surrogates to resemble typical organic fouling by real surface waters remains questionable. Therefore, there is an imperative need for an appropriate lab-scale testing protocol employing reliable fouling surrogates. In this study, an application-oriented testing protocol employing mini-plant testing unit was developed. Performance of new modified membrane modules was investigated and compared with performance of commercially available Multibore® modules, as standard membrane, at conditions close to full-scale application. Potting soil extracts were investigated as reliable and inexpensive model foulants. They were comprehensively characterized and compared with real surface water samples as well as commonly reported fouling surrogates (humic acid, bovine serum albumin, alginate, colloidal silica). Potting soil extract feeds were emphasized to imitate chemical composition and characteristics of moderately organic-loaded surface waters, at high reproducibility, and induce typical organic fouling within experiment time. At comparable total organic carbon content, aqueous extracts of four potting soil types had different dissolved organic carbon compositions and turbidity. Humic substances were the main constituents; however, hydrophobic organic carbon (HOC) and biopolymers varied significantly. Feeds exhibiting high biopolymer content or a combination of biopolymer and HOC were able to distinguish explicitly between fouling propensity of different modified membrane materials. Besides regular performance measures, fouling propensity was quantified as hydraulic irreversible fouling index (HIFI). This fouling index was correlated to the turbidity removal; however, no consistent correlation was found between HIFI and humics as well as low molecular weight organic fractions in the potting soil extracts. Furthermore, impact of feed solution type on the interplay between membrane characteristics and HIFI values was investigated. Good correlation between PPSU-based membrane characteristics and HIFI values was noticed upon using feeds containing considerable biopolymers and HOC portions. Nonetheless, no reliable correlations could be observed in case of PESU-based membranes which was attributed to the dominant impact by more relevant parameters, i.e., pure water permeability.
Im Rahmen des MABMEM-Forschungsprojekts wurden neu entwickelte Polyethersulfon (PESU) -basierte und Polyphenylensulfon (PPSU) -basierte Single-Bore-Hohlfaser-UF-Membranen in standardisierten Foulingversuchen verglichen und bewertet. Um eine zuverlässige Entscheidung bezüglich vielversprechender Membrankandidaten innerhalb einer angemessenen Versuchszeit treffen zu können, war es entscheidend, Filtrationsexperimente im Labormaßstab zu gestalten, die den Prozess im technischen Maßstab bestmöglich abbilden. Bisherige Untersuchungen zur Leistungsfähigkeit von Ultrafiltrationsversuchen im Labormaßstab wurden überwiegend unter Verwendung von Flachmembranen und bei Betriebsbedingungen durchgeführt, die den realen Anwendungsfall nur unzureichend widerspiegeln. Darüber hinaus werden die verwendeten Feed-Lösungen meist aus natürlichen Rohstoffen hergestellt, was die Qualitätssicherung über längere Zeiträume schwierig macht. Gleichzeitig ist die Fähigkeit von synthetischen Fouling-Surrogaten („Foulants“), organisches Fouling durch reale Oberflächenwässer zu simulieren, fraglich. Es besteht folglich ein hoher Bedarf an zuverlässigen Fouling-Surrogaten sowie aussagekräftigen Testprozeduren im Labormaßstab.