AWWA WQTC69380

The objective of this study was to reproduce a comprehensive catalogue of the effect that ultrasound has across all problematic blooming algal species. A range of algal species were tested including cyanobacteria species Microcystis aeruginosa and Aphanziomenon flos-aquae, a green alga Scenedesmus subspicatus and a wild type diatom Melosira sp. The experiments were performed using laboratory scale ultrasonic equipment covering frequencies between 20 kHz and 1.15 MHz, and power ranges of 200-420Watts. Key results have demonstrated a relationship between energy input per unit volume and cell removal efficiency. For instance Microcystis aeruginosa needed 100kWh/m³ at a frequency of 20-30 KHz to remove 60% of cells, after which no bloom recovery can occur. Aphanziomenon fq. required lower energy only 20-30kWh/m³ but a higher frequency of 1144kHz for 100% cell removal. Coupling the removal data and Chlorophyll fluorescence and TEM imaging has enabled the impact of ultrasound and algal physiology to be established. When the energy input increases beyond 278kWh/M³ critical cell rupture is reached producing removal rates of 60% for Microcystis aeruginosa below this energy level limited removal is observed which is thought to be due to the inability of cell rupture to occur. The paper concludes by comparing ultrasound to other algal removal technologies to establish under which situation it becomes the most appropriate technology selection. Includes 21 references, figures.