Ultrasonic cleaning of nylon microfiltration membranes fouled by Kraft paper mill effluent

An ultrasonic technique was successfully applied to remove fouling and recover the permeate flux of flat sheet microfiltration (MF) membranes. Three kinds of cleaning methods were used, namely: forwardflushing, ultrasonic cleaning and ultrasound with forwardflushing, and their cleaning efficiencies were compared. It was found that ultrasound associated with forwardflushing was a new effective method for the recovery of permeate flux. Scanning electron microscopy (SEM) analysis indicated that this method was able to remove fouling layers from a membrane surface and restore the original structure of the membrane surface. The operating conditions during cleaning were investigated. In general, a high forwardflushing velocity and low cleaning solution (water) temperature, under the same ultrasonic conditions, gave higher cleaning efficiency. Moreover, online ultrasound can reduce membrane fouling and enhance permeate flux. The horn sonicator employed had a frequency of 20 kHz and a power of 375 W. Fouling and cleaning experiments were performed with nylon membranes with 0.2 μm average pore diameter. The membranes were fouled by Kraft paper mill effluent.