Cleaning of particle-fouled membranes during cross-flow filtration using an embedded ultrasonic transducer system

Ultrasound was introduced into an “off-the-shelf” cross-flow membrane cell using a Navy Type I lead zirconate titanate transducer embedded opposite a membrane surface. The transducer, only 4.1 mm in thickness, required minimal modification of the existing flat-sheet filtration cell. Hydrogen peroxide and chemiluminescence measurements indicated that the thin transducer system was capable of inducing cavitation, and that the extent of cavitation increased with increasing applied power. For all powers tested, chemiluminescence measurements indicated that the surface of the membrane in the cross-flow system was within the zone of cavitation. Membranes were then fouled by 0.53 μm sulfate polystyrene latex particles. Membrane cleaning results showed that the thin transducer system increased the permeate flux of the membrane, with flux increasing with increasing applied power to the transducer. Both pulsed and continuous operation of the transducer improved flux (with continuous operation resulting in slightly greater improvement), although it may be beneficial to operate the system in pulsed mode to reduce energy consumption. At the highest powers, some damage to the membrane was observed. At lower applied powers, however, no damage to the membrane was found.