In this study, the efficiency of ultrasonic disruption of Chaetoceros gracilis, Chaetoceros calcitrans, and Nannochloropsis sp. was investigated by applying ultrasonic waves of 0.02, 0.4, 1.0, 2.2, 3.3, and 4.3 MHz to algal suspensions. The results showed that reduction in the number of algae was frequency dependent and that the highest efficiency was achieved at 2.2, 3.3, and 4.3 MHz for C. gracilis, C. calcitrans, and Nannochloropsis sp., respectively. A review of the literature suggested that cavitation, rather than direct effects of ultrasonication, are required for ultrasonic algae disruption, and that chemical effects are likely not the main mechanism for algal cell disruption. The mechanical resonance frequencies estimated by a shell model, taking into account elastic properties, demonstrated that suitable disruption frequencies for each alga were associated with the cell's mechanical properties. Taken together, we consider here that physical effects of ultrasonication were responsible for algae disruption. HighlightsThe disruption of algae is frequency dependent and algae specific.The resonance frequencies of algae are calculated using elastic modulus measures.Cavitation bubbles are necessary for the algae disruption process.Chemical effects are not the main mechanism for algal cell disruption.Suitable disruption frequencies are associated with the cell's mechanical properties.

In this work the effect of ultrasonic waves on suspensions of Chlamydomonas concordia and Dunaliella salina have been investigated at frequencies of 20, 585, 864 and 1146 kHz and at different acoustic powers. Results showed that the reduction in algal numbers was dependent on both frequency and acoustic power. The order of efficiency of the ultrasonic disruption of C. concordia at different frequencies was 20 < 580 < 864 < 1146 kHz, and for D. salina was 20< 580 ≅ 864 ⩽ 1146 kHz. It is clear that high-frequency sonication is more effective than conventional low-frequency sonication for the disruption of cells for both species. Results showed that suitable disruption frequencies for each algae were associated with the mechanical properties of the cell. The frequency dependence of the efficiency of algae disruption on the mechanical resonances of both the algae cell is discussed in terms of bubble oscillation in an ultrasonic field.

The sonoelectrochemical degradation of phenol in aqueous solutions with stainless steel electrodes and high-frequency ultrasound (850kHz) was investigated. A 60% synergetic effect was obtained in the combined reaction system. High concentration of electrolyte (sodium sulfate) and a high electrical voltage are favorable conditions for the degradation of phenol. A nearly complete degradation of phenol was achieved with 4.26g/L Na(2)SO(4) and 30V electrical voltages at 25°C in 1h. The degradation of phenol follows pseudo-first order kinetics. Considering costs and application, the energy efficiency of the reaction system with different reaction conditions was evaluated.

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