Xianfu Chen

Self-cleaning Piezoelectric Membrane for Oil-in-water Separation

Ultrasound (US) treatment coupled with membrane filtration has been utilized for membrane fouling control in water treatment; however, large-scale implementation of ultrasonic cleaning equipment appeared to be cost-prohibitive. In this study, a porous lead zirconate titanate (PZT) membrane is presented that enables in situ ultrasound generation by the application of an alternating voltage (AV) to mitigate fouling during oil-in-water (O/W) emulsion separation. We expect that this method is much more cost-effective because it is more direct, avoiding buildup of fouling and the need to take the membrane offline. Because the PZT membrane is hydrophilic, its underwater surface is oleophobic so that the accumulated oil droplets will have little affinity and hence can be removed easily by in situ-generated US. The effect of the in situ US generation on membrane fouling was investigated through variation in the excitation AV and its frequency, O/W emulsion pH, emulsified oil concentration, crossflow velocity, and transmembrane pressure. The results indicated that the in situ US generation resulted in a substantial decrease of fouling during the filtration process of O/W emulsions, whereas the membrane flux was maintained closely at its initial value.

1.11 Ceramic Membranes

The article reviews the fabrication and application of ceramic membranes and provides a comprehensive overview of structure–property relationships of ceramic membranes in various important applications to establish an application-oriented material design method. Due to the high amount of flux, great separation efficiency, and long lifetime, with a continuous decrease in fabrication costs, research on ceramic membranes is fast increasing, and ceramic membranes have become more competitive. Here, some novel fabrication techniques, including a pore-forming agent method, a fiber construction method, and a modified sol–gel route, are discussed extensively. Further research has been reported to produce membranes with a wide range of unique microstructures and surface properties, which can be adapted for the application and increase of their market volumes. Finally, five industrial applications (ceramic membrane reactors, oily wastewater treatments, biological fermentation treatments, plant extracts, and brine refinements) are introduced.