Evaluation of power ultrasonic effects on algae cells at a small pilot scale

Abstract

It has been recognized for several years that power ultrasound can effectively inactivate algae cells at a laboratory scale. However, although ultrasonic inactivation shows great potential, there are few reports of its use when applied on a large scale. In this study, we have investigated the uses of two types of ultrasonic equipment at a small and medium laboratory scale for the control of algae blooms which are commercially available in similar configurations for industrial scale operation. The following equipment was tested using cultured algae suspension: (a) Dual Frequency Reactor (DFR) operating on 1 L in batch mode and 3.5 L in recirculating mode with two resonating plates at different frequencies of 16 and 20 kHz (Advanced Sonic Processing Systems, USA); (b) Sonolator operating in a flow mode treating 5 L using hydrodynamic cavitation (Sonic Corporation, Stanford, CA, USA). The most effective inactivation was obtained using the DFR in batch mode at 60% power setting for 10 min which resulted in a reduction of 60% of the original concentration (measured using optical density OD). In a recirculating loop mode, the treatment of 3.5 L algae suspension with a DFR for 15 min resulted in a reduction of 46% (OD). Ultrasonic treatment of 5 L suspension in a recirculating loop using the Sonolator over 5 h resulted in a reduction of 30% (OD). This study is the first to explore the use of two commercially available ultrasonic systems (DFR and Sonolator) both capable of direct scale-up to industrial levels for the control of algae. It demonstrates that sonication in a recirculating process has the potential to be effective in the treatment of algal cells on a large scale.