Self-cleaning performance of in-situ ultrasound generated by quartz-based piezoelectric membrane

Membrane separation technology is playing a prominent role in treatment of suspension wastewater, but its efficiency is limited by membrane fouling. Here, a self-cleaning piezoelectric ceramic membrane (PCM) coupled with in-situ ultrasound functionality was developed. The PCM consists of a porous piezoelectric quartz (ɑ-SiO₂) support and a ZrO₂ microfiltration (MF) layer. The MF layer serves as a separation membrane, and it possesses a smooth and negatively charged surface, which is beneficial to weaken the interaction between membrane and foulants. The ɑ-SiO₂ support provides mechanical strength to the membrane and can generate internal ultrasound to mitigate fouling. In MF process, particulate foulants are inevitably deposited on the membrane surface, forming a cake whose permeance resistance is 3.9 times of pristine membrane. With the assistance of internal ultrasound, the thickness of cake decreased from 64.2 to 48.4 μm, and porosity increased from 39.5% to 42.5% due to the formation of shear force. Higher cross-flow velocity and more vigorous ultrasound intensity are helpful to strengthen turbulence, which can improve stationary membrane flux by 41.7%. The fouling removal efficiency of internal ultrasound is superior to the outer one, and the economic evaluation indicates that the cost of water production can be saved in the presence of ultrasound.