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One of the most popular means for removal of organic water pollutants found in small concentrations is by adsorption. An important step in adsorption processes is the regeneration of the adsorbent as it does not only affect the adsorption-desorption cycle but also the expenses of the following process steps. State of the art regeneration of adsorbent resins is done by chemical methods. These require the use of organic solvents or inorganic chemicals and involve a difficult secondary separation step. Therefore, industry seeks for alternative methods to regenerate exhausted adsorbents. One of the discussed regeneration methods is desorption by ultrasound. Ultrasound does not only promote desorption but also enhances the mass transfer of sorption processes. We discuss the arising problems and basic effects when applying ultrasound during sorption processes in order to show the potentials of this desorption process. The focus is laid in particular on the influence of ultrasound frequency and intensity.

The following paper is aimed at finding the effects of ultrasound on adsorption/desorption processes. Experiments concerning the ultrasonic power input indicate that particles absorb ultrasonic energy effectively if they are in resonance with the ultrasound. The ultrasonic energy is dissipated into heat. Hence, desorption processes are promoted. Desorption experiments at different frequencies show that neither particle oscillations nor cavitation effects are responsible for ultrasonically enhanced desorption processes for an adsorption system with surface diffusion as the rate-limiting step. Measured ultrasonic power distributions show that the ultrasonic field inside the adsorber is very inhomogeneous. With the temperature distribution inside the adsorber, the courses of concentration of ultrasonically enhanced desorption experiments can be explained by a hot-water desorption model. Thus, simulations substantiate the experimental results that thermal effects are responsible for ultrasonically enhanced desorption with the applied adsorption system.

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