Relative impact of fouling and cleaning on PVDF membrane hydraulic performances

The long-term decrease of hydraulic performances observed in membrane systems is generally explained by the gradual accumulation of irreversible foulants. Although the use of chemicals is primarily aimed to remove most of the foulants, few studies have reported their potential degradation impact on the membrane, consequently leading to the decrease in hydraulic performances. However, the impact of chemical ageing on the intrinsic membrane characteristics has not been studied in details, and the understanding of its relative role in the long-term filtration behaviour is, so far, limited. In this study, a polyvinylidene fluoride (PVDF) micro-porous membrane was aged through long-term fouling/cleaning cyclical experiments using model organic and 20,000 ppm sodium hypochlorite (NaOCl) solutions. The membranes were then thoroughly characterised, both physically and chemically, by various analytical techniques. The apparent pore size of the aged membrane was observed to enhance due to the combined effect of increased wetting and hydrophilicity of the membrane. Furthermore, NaOCl exposure led to early degradation of the PVDF membrane through cross linking and thus, slight loss of its mechanical properties. The impact of NaOCl on PVDF tensile properties was found to be less pronounced on fouled membranes, revealing the relative role of fouling during membrane ageing.

► NaOCl cleaning resulted in PVDF membrane pore size enhancement.
► The observed membrane ageing was less pronounced when the membrane was fouled.
► Fouling played a significant role in the relative ageing of the membrane.