Cleaning Efficiency of Ultrasound in Various Polymeric Membrane Modules

Attentions to use of ultrasound for cleaning of polymeric membranes are less thanone decade. In this experiment, the cleaning efficiencies of various frequencies of ultrasound in different membrane modules and the barrier effect of structural design and membrane module during cleaning process using ultrasound were evaluated. Three membranes, hollow fiber without module, flat sheet membrane including stainless steel and acrylic module and spiral wound with polyethylene modules applied during forward flushing cleaning process by ultra pure distilled water for 30 minutes after fouling by skimmed milk 1% using ultrasonic irradiation of 28, 45 and 100 kHz frequencies in constant intensity of 300W. The permeate flux and hydrodynamic resistance of new,fouled and cleaned membranes during sonication using various frequencies of ultrasound were determined separately. In this manner the cleaning efficiency of each treated membranes were calculated The data statistically analyzed using ANOVA table. The results showed that the most cleaning effects obtained in all tested membranes by various frequencies of ultrasound at first 5 minutes of cleaning process. The highest amounts of cleaning effect achieved in hollow fiber membrane using all tested frequencies especially in 28 kHz. The maximum cleaning efficiency achieved more than 95 percent for the first 5 minutes and may be due to lack of barrier such as holder or membrane support in the design of this membrane module. However, we observed the cleaning efficiency of 92 percent after 30 minutes in flat sheet membrane module using ultrasoundin28 kHz and the amounts of cleaning efficiencies in same conditions were lower than hollow fiber module. The other tested frequencies were not significant cleaning effects and stainless steel and acrylic holders in design of membrane module prevented to reach of sonic power to surfaces and pores of flat sheet membrane. The minimum ultrasound cleaning efficiency achieved in spiral wound membrane modules only 21 percent after 30 minutes ultrasonication using 28 kHz during forward flushing and it seems that only outside of membrane surfaces are affected. This is may be due to special design of membrane module and barrier effects of configuration and membrane holders.