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This paper investigates a methodology for the characterisation and location of a thin layer of irreversible fouling in a spiral-wound ultrafiltration membrane by using several physico-chemical techniques as SEM-EDX, SEMFEG, FTIR-ATR and AFM. Application to analysis of a spiral-wound PES membrane for UF of skimmed milk, after 4 years of production in a French dairy plant, is detailed. From the analyses, it was evidenced that all parts of the spiral module did not have the same behaviour towards fouling and cleaning. The mapping obtained from SEM-EDX shows that irreversible fouling is located near the collector axis of the permeate and is independent of the inlet and outlet of the membrane. Significant differences are observed between the inner/outer and middle sheets of the spiral membrane. This is probably closely connected with the distribution of the fluid velocity in the spiral membrane. It would be important to compare such analyses with now available computational fluid dynamics (CFD) data related to this complex spiral geometry. Such an approach would lead to improvement of the cleanability of such systems.

This paper aimed at giving a methodology based on the analysis of a thin fouling layer on a spiral membrane through several physico-chemical characterisations. SEM-EDX and FTIR-ATR appeared to be efficient and complementary tools to achieve this objective, both from the qualitative and quantitative points of view. In order to overview the most fouled sheet in the spiral membrane, a better way seems to be the analysis of the inner membrane (membrane 1, Fig. 1). Selection of only 4 samples was needed, located in the middle part of the sheet (location 2–5–8–11, Fig. 2). Some differences could be observed from one membrane sheet to another, and the borderline sheets (sheet 1, sheet 7) appeared to be the most fouled. For a better understanding, a comparison of inner and outer sheets is recommended, as all parts of the spiral module do not behave in the same way towards fouling and cleaning. From SEM-EDX (Figs. 8 and 9) on the main components of the fouling layer it is possible to describe in a more refined way the location of organic irreversible fouling, leading to relevant mapping of the whole spiral membrane. Such data could be used as a guideline to study the distribution of the fluid velocity in the spiral membrane and at least it would be of importance in computational fluid dynamic validation. So far, easy access to such a significant amount of experimental data from both SEM-EDX and FTIR-ATR is mandatory. However the sampling of parts of the spiral membrane for systematic analyses could be adapted based on our work to be close to any chosen network of numerical calculations.