(410c) Studies On Ultrasonic Backwashing of Monolith, Multi-Channel Ceramic Module to Minimize Ultrafiltration Fouling

Ultrafiltration fouling is a major issue in many industries, including water treatment, dairy, food, biochemical and pharmaceutical, which results in permeate flux decline, resulting in larger membrane areas and increased liquid pressure drop. Ultrasonic techniques have been used with some success in reducing concentration polarization and membrane fouling, though practical applications have been limited by the fact that the ultrasonic energy intensity needed to achieve significant permeate flux enhancement results in faster membrane deterioration, especially with polymeric membranes. With tubular stainless steel and ceramic membranes, which are more robust to physical deterioration, applying ultrasonic energy directly on the membrane surface is practically difficult due to the rounded shape of the tube, rapid attenuation of the ultrasonic energy with distance from the transducer and within the tortuous membrane pores, and possible degradation of the fluid material due to temperature increases, especially in food and dairy applications.

In this paper, the application of ultrasonic energy to inhibit concentration polarization and surface fouling will be reviewed and discussed. Bench-scale results will be presented on studies, conducted with several solute systems, including polyethylene glycol, casein, dextran, polyethylene imine and actual commercial laundry water, using a multi-channel ceramic membrane, wherein the separating membrane is on the outside surface of the monolith, with multiple internal channels for the permeate, and ultrasonic energy is applied to the permeate side, causing rapid, reproducible, high frequency back-washes of the membrane surface. This constant, dynamic perturbations of permeate pressure, resulting in short-pulse duration backwashes of the membrane, prevents the formation of concentration gradients on the feed side and keeps the convective diffusion of small particles into the membrane pores, thereby maintaining high permeate flux, even with high feed solute concentrations. Results of the experimental study and a mathematical model, which provides a systematic approach for selecting the ultrasonic frequency and amplitude, will be presented in this paper.