Acoustic Methods for Fouling Characterization

The method was also applied to an inside/out tubular membrane [8] during UF of 0.08 g bovine serum albumine (BSA) solution. The tubular membrane used was a polyethersulfone (PES) membrane with a M WCO = 40 kDa, and with inside and outside diameters of 14 mm and 21 mm, respectively. It was possible to detect and distinguish the acoustic response signal from the various interfaces. The 

The monitoring of membrane fouling with acoustic waves is one of the few non-invasive methods potentially applicable to commercial-scale modules. Nonetheless, amplitude measurements can only provide qualitative characterization (relative amplitude variations) of the cake formation process because of the lack of knowledge about the propagation mode of an acoustic wave in a deformable deposit. 

Most of the studies about the use of acoustic waves for fouling characterization gave qualitative information about the cake layer (relative amplitude variations) and concerned flat-sheet membranes. The originality of the method presented here [9] is to give the possibility of extracting qualitative information by using another characterization method in parallel. 

The acoustic method can be applied on various materials which do not need to be transparent. There is a no constraint for the filtration module expected that the filtration surface has to be larger than the acoustic sensor (generally a circle, diameter 4-10 mm). 

A step in the development of the acoustic technique for the monitoring of membrane processes is to choose a frequency adapted to the membrane material. Therefore, several frequencies have to be tested (usually in the range 1-10 MHz). The adapted frequency must result in a workable signal, with large amplitude and well separated waves. Some frequencies can be cut by the membrane material, that is to say totally absorbed. Usually, each material has its own adapted frequency. 

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