Characterisation of cleaned and fouled membrane by ATR–FTIR and EDX analysis coupled with SEM: application to UF of skimmed milk with a PES membrane

The cleaning of an ultrafiltration polyethersulfone (PES) membrane fouled by skimmed milk was studied by ATR–FTIR showing the functional groups of fouling species and EDX coupled with SEM measuring the atomic composition. Two kinds of fouling conditions were studied: further so-called “static conditions” as performed in a beaker and “dynamic conditions” as performed on a UF loop with applied pressure. For static conditions, all milk components (proteins, lactose, ions) adsorbed on the PES surface. Lactose and salts were eliminated by water rinsing, whereas proteins were only partially desorbed by chemical cleaning at basic pH. For dynamic conditions, the cleanliness of the membrane was evaluated through two criteria: hydraulic (recovery of initial flux) and chemical (no more contaminants detected). The hydraulic cleanliness of the membrane was achieved whereas the membrane initial surface state was not restored.

This paper shows that ATR–FTIR and EDX– SEM are well adapted techniques to characterise a membrane surface and study its cleanliness. Despite the fact that they are destructive techniques, they can to be used as efficient complementary tools to flux measurements. Comparative studies by adsorption without pressure were not efficient enough, and use of UF conditions appeares as essential. The flux recovery can be achieved without chemical cleanliness of the membrane and the efficency of the cleaning solution cannot be simply relied to its surface tension (Table 1). The question of accumulation on the membrane after several UF/cleaning cycles, not investigated here, is opened.