Fouling autopsy of hollow-fibre MF membranes in wastewater reclamation

Fouling in membrane filtration processes is problematic but inevitable as it occurs with the retention of contaminants that accumulate on the membrane surface. The causes of fouling are often specific, depending upon feed water constituents, the membrane, and the operation regime. Therefore, it is desirable that a thorough investigation is performed on fouled membrane elements of the affected plant. This technique is known as “membrane autopsy”, which identifies the cause of poor membrane performance, and hence, gives the opportunity to rectify or mitigate the problem and improve future plant design. The cause of membrane fouling at a small water recycling plant using a hollow-fibre microfiltration system was investigated. A membrane autopsy protocol was developed for water recycling applications that consists of four major steps: (1) tensile testing to investigate the membrane mechanical integrity, (2) direct visual inspection, (3) membrane surface analysis using field-emission environmental scanning electron microscopy (as well as atomic force microscopy, although it is not used in this case) techniques, and (4) foulant constituent analysis. Results obtained from this study indicate that the membrane was fouled by a mixture of colloids and organic matters, enhanced by the presence of multivalent cations. Possible measures to mitigate fouling in this particular case have also been suggested.