Ultrasound as a means of detaching biofilms

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Abstract
It is well known that ultrasonic baths are suitable for cleaning surfaces. In order to investigate the mechanisms of the cleaning effect a simple experimental arrangement with an adjustable ultrasonic transducer was developed. Reverse osmosis membrane samples colonised with a monolayer of fast adhering bacteria were exposed to defined ultrasound. A threshold for detachment was defined if more than 95% of the bacteria were removed. Detachment rate was found to depend on (i) the sound intensity (threshold 2 Watt), (ii) the time of exposure (60 s) and (iii) the distance between transducer and membrane (4 cm). The shear forces in the acoustic boundary layer are considered to be responsible for the detachment of the bacteria. The first results reveal that the application of ultrasonic waves provides a tool both for cleaning biofouled surfaces and for investigating the adhesion forces of microorganisms to surfaces.