Factors influencing the ultrasound-enhanced cleaning process of an ultrafiltration ceramic cembrane fouled by reactive dye particles

摘要

Membrane processes such as Ultrafiltration (UF), Nanofiltration (NF) and Reverse Osmosis (RO) are widely employed in the treatment of textile wastewater because of the versatility of this technology [1]. Unfortunately, one of the critical issues in the development of membrane processes is the decline in system performance due to membrane fouling, which limits the economic efficiency of the process. Membrane fouling is generally characterized as a reduction of permeate flux through the membrane as a consequence of several mechanisms [2]. This phenomenon imposes the need for the frequent cleaning of the membrane. Therefore, an improvement of the cleaning procedure may have significant influence on the overall process efficiency. The use of chemical agents like acid, alkali, surfactants, enzymes or hypochlorite is a common membrane cleaning procedure. However, these methods may be unsafe and expensive. In addition to chemical treatments, there are several other methods to reduce membrane fouling based on physical operations: hydrodynamic forward or reverse flushing, permeate back pressure, ultrasonication, cleaning under magnetic or electrical fields, among others [3]. Of particular interest to the present work is the use of ultrasound in order to reduce membrane fouling and to improve the membrane cleaning efficiency. Ultrasound (US) is a sound wave traveling through a medium at a frequency above 18 kHz. When ultrasound is irradiated through a liquid medium, an alternating rarefaction and compression of the medium occurs. During the rarefaction stage, the formation and growth of micro bubbles may take place. The compression cycle makes bubbles collapse, releasing sufficient energy to overcome the interaction between the foulant and membrane and to remove the foulant from the surface of the membrane [4].