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Long-term nanomechanical changes of polymeric ultrafiltration (UF) membranes caused by fouling/cleaning agents in water treatment are not well established in the literature. The goal of this study was to investigate the nanomechanical properties of polymeric UF hollow fiber membranes operating at a pilot-scale for 449 d and subjected to a low-quality feed (i.e., high turbidity/TOC content). Quantitative nanomechanical mapping technique was used to measure the deformation, dissipation, modulus, adhesion, and roughness of the polymeric structures of commercial Aquaflex virgin membranes, harvested membranes, and foulant layers. Results indicated that the recalcitrant and heterogeneous nature of the foulants absorbed on harvested membranes showed low elastic properties, and high modulus, adhesion, and roughness. The strong affinity of these foulants towards membrane surface would alter membrane characteristics and influence subsequent fouling behaviour. The cleaning process and extended operation did not significantly affect the nanomechanical properties of membranes. Despite the low-quality feed, the three modules were only subjected to 37 chemical- enhanced backwashes and filtered a total volume of 2.155 m³. These results indicate the importance of operating conditions (i.e., frequency of backwash/cleaning/disinfection steps) and feed quality on the long-term changes of UF membranes and would assist in identifying research directions that are necessary to minimize membrane fouling/ageing. [ABSTRACT FROM AUTHOR]

This study analyzed the change in nanomechanical properties of ultrafiltration hollow fiber membranes harvested from pilot-scale units after twelve months of operation. Quantitative Nanomechanical Mapping technique was used to distinguish between adhesion, dissipation, deformation, and modulus while simultaneously generating a topographic image of membranes. Nanomechanical maps of virgin membranes evidenced surfaces of heterogeneous properties and were described by probability density functions. Operating conditions and feed quality exerted an impact on membranes. Clean harvested membranes showed a higher mean modulus and dissipation, and a lower deformation than virgin membranes, indicating stiffer membranes of lower elastic deformation. A significant fraction of these measurements displayed peak values deviating from the distribution; which represents regions of the membrane with properties highly differing from the probability density function. The membrane polymeric material experienced severe physicochemical changes by foulant adsorption and reaction with cleaning agents. Foulant adsorption on membranes was heterogeneous in both morphology and mechanical properties and could not be statistically described. Foulants, i.e., mainly consisting of polysaccharides and proteinaceous structures, displayed low elastic deformation and high roughness and adhesion. The presence of foulants after chemical cleaning and their high adhesion would be a direct nanoscale evidence of irreversible fouling. By the end of the operation, the Trans-Membrane Pressure experienced a 40% increase. The cleaning process was not able to fully recover the initial TMP, indicating irreversible fouling, i.e., permanent change in membrane characteristics and decrease in performance. These results suggest a link between the macroscopic properties and nanomechanical characteristics of membranes. This study advances our nanoscale understanding of the impact of fouling and operating conditions on membranes characteristics. [ABSTRACT FROM AUTHOR]