Time-dependent analysis of polysaccharide fouling by Hermia models: Reveal the structure of fouling layer

• Time-dependent forward and reverse Hermia model fitting was used to process the filtration data. • The new fitting method declared the membrane fouling mechanism and fouling layer structure. • The Hermia classic model is more appropriate for processing the filtration data with Ca 2+ in cross-flow filtration. • The Hermia mass-transfer model is more suitable for fitting the filtration data with Mg 2+ in cross-flow filtration. The Hermia fouling models are often applied in interpreting filtration data to reveal the fouling mechanisms. However, the application of these models is arbitrary and lacks in-depth analysis. In this study, time-dependent Hermia models with forward and reverse processing were employed for the first time to analyze the membrane fouling mechanism and fouling layer structure determined by polysaccharide in dead-end and cross-flow filtration. The applicability of Hermia classic and mass-transfer models was also investigated. Results showed that in cross-flow filtration, the Hermia classic model is more suitable for processing the filtration data with Ca 2+ and the Hermia mass-transfer model is more appropriate for fitting the experiment result caused by Mg 2+ owning to the differences in affinity of Ca 2+ and Mg 2+ to polysaccharide. Fitting results further manifested that the differences in concentration could obviously affect structure of polysaccharide fouling layer, and the introduction of Ca 2+ and/or Mg 2+ changed the spatial conformation and compactness of fouling layer. These results suggested that Hermia fouling models can provide insightful analysis of the fouling layer structure from micro-level to interpret the fouling mechanisms. The influence of cation concentration and type on membrane fouling can be revealed by the processing of Hermia models. In short, time-dependent forward and reverse processing of Hermia classic and mass-transfer models could preliminarily explain the membrane fouling behavior and structure of fouling layer. This work suggests that the Hermia fouling models are more useful than we thought and the time-dependent application of them could provide deep insights into fouling development.