Ageing of PES industrial spiral-wound membranes in acid whey ultrafiltration

The objective of this paper is to characterise and locate the thin layer of irreversible fouling in a spiral-wound membrane of ultrafiltration of acid whey, after 8000 h of production in a French dairy. Several physico-chemical techniques as SEM-EDX, SEM-FEG, FTIR-ATR and AFM were used. Fouling was mainly organic and between 0.5 and 5 µg of proteins per cm2 of membrane were reached. The thickness of the fouling layer was higher at the collector axis of permeate and decreased with the distance from this axis on an unwound sheet of the membrane. Ageing of both PES active layer and polypropylene spacers was evidenced by this autopsy. In-depth study was achieved at 50°C for PES membrane ageing in alkaline, acid, alkaline chlorine oxidant and a commercial alkaline cleaning solution (Ultrasil 10). The PES membrane appeared stable in all solutions except those containing chlorine. It was shown by FTIR-ATR that the C–S bond in PES (Ph–SO2–Ph) was broken and led to a Cl–S bond after longterm treatment in alkaline bleach.

This paper aimed to analyse a spiral module at the end of its service life after 8000 h of acid whey ultrafiltration. Physico-chemical characterisations by SEM-EDX and FTIR-ATR were efficient and complementary tools to fulfil this objective both from a qualitative and quantitative point of view. As the active layer of the spiral membrane was highly damaged, we have performed an in-depth study of the PES membrane ageing. It was shown by SEM-EDX that PES degradation was due to bleach used in the disinfection step. Moreover FTIR-ATR allowed the identification of the breakage of the C–S bond of the PES.