Dynamic analysis of ultrafiltration membrane fouling based on in-situ solid-phase fluorescence optic fiber (SPFOF): Fouling mechanism and cake layer structure

Membrane fouling is an important obstacle to the development of membrane technology, and understanding the fouling mechanism and the sequential structure of the cake layer is critical for fouling control. In this study, a solid-phase fluorescence optic fiber (SPFOF) platform was established, combined with parallel factor analysis (PARAFAC) and response surface methodology (RSM), to achieve quantitative monitoring of mixed foulants on the membrane surface. The membrane fouling mechanism and cake layer structure were further investigated. The results indicated that the deposition amount of protein (PN) substances exhibited a linear positive correlation with fluorescence intensity, whereas solid-phase humic acid (HA) demonstrated a fluorescence quenching effect. The intermediate blocking and cake filtration were identified as the dominant membrane fouling mechanisms. The membrane fouling of PN and HA had spatiotemporal dynamic changes during the filtration process. Initially, PN was preferentially adsorbed onto the membrane surface, followed by the rapid deposition of HA facilitated by the subsequent formation of the PN-HA structure. Compared with liquid excitation-emission matrix and chemical concentration methods, the SPFOF method had both accuracy and repeatability, and had significant advantages in the quantitative characterization of foulants at the interface of the membrane.