Recent advances in ultrasonic treatment: Challenges and field applications for controlling harmful algal blooms (HABs)

Abstract

Algal blooms are a naturally occurring phenomenon which can occur in both freshwater and saltwater. However, due to excess nutrient loading in water bodies (e.g. agricultural runoff and industrial activities), harmful algal blooms (HABs) have become an increasing issue globally, and can even cause health effects in humans due to the release of cyanotoxins. Among currently available treatment methods, sonication has received increasing attention for algal control because of its low impact on ecosystems and the environment. The effects of ultrasound on algal cells are well understood and operating parameter such as frequency, intensity, and duration of exposure has been well studied. However, most studies have been limited to laboratory data interpretation due to complicated environmental conditions in the field. Only a few field and pilot tests in small reservoirs were reported and the applicability of ultrasound for HABs prevention and control is still under question. There is a lack of information on the upscaling of ultrasonication devices for HAB control on larger water bodies, considering field influencing factors such as rainfall, light intensity/duration, temperature, water flow, nutrients loading, and turbidity. In this review article, we address the challenges and field considerations of ultrasonic applications for controlling algal blooms. An extensive literature survey, from the fundamentals of ultrasound techniques to recent ultrasound laboratory and field studies, has been thoroughly conducted and summarized to identify future technical expectations for field applications. Case studies investigating spatial distribution of frequency and pressure during sonication are highlighted with future implications.

Algal Morphological Identification in Watersheds for Drinking Water Supply Using Neural Architecture Search for Convolutional Neural Network

“…causes clogging of filtration systems in drinking water utilities [3,[8][9][10]. Various physical, chemical, and biological methods (e.g., algaecides, nano-materials such as TiO 2 , barley straw, and ultrasonication) [11][12][13][14] and the reduction of nutrients in water bodies by utilizing a wetland or a natural predator of algae, such as Daphnia, [15] have proven effective for the control of algal blooms. While the control and mitigation of algal blooms in freshwater systems is important for safe drinking water supply, proper monitoring of the occurrence and physiological status of the algal bloom is imperative for developing effective water resource management strategies [16].…”

200 kHz Sonication of Mixed-Algae Suspension from a Eutrophic Lake: The Effect on the Caution vs. Outbreak Bloom Alert Levels

“…In contrast, stating the attenuation of power intensity in large volumes of water, inconsistent effects in some field trials and the effect of high ultrasound intensity on non-target organisms, such as Daphnia magna, some researchers highly doubt the effectiveness of sonication in field applications, such as whole lake settings [39,56]. However, in their recent literature review, Park et al [29] argue that ultrasonication is still an attractive technique in many aspects compared to other technologies for algal control, especially compared to the use of algaecides. The energy requirement can be managed using floating devices and the sun, and unlike chemical treatment techniques, ultrasound is a clean technology that does not produce any byproducts [14].…”

“…The energy requirement can be managed using floating devices and the sun, and unlike chemical treatment techniques, ultrasound is a clean technology that does not produce any byproducts [14]. Several approaches are proposed to scale up sonication, such as the deployment of multiple floating ultrasonic devices to supply sufficient ultrasound intensity, restricting treatment target areas to locations close to water intake towers, as the removal of algae from a large reservoir entirely may not be realistic considering the cost, conducting several field/pilot studies considering water flow, targeted algae species and other natural water body related operation factors, and combining sonication with remote sensing technologies to measure the algal concentration and optimize the application time [29]. The successful field application by Schneider et al [16] is encouraging to emphasize more systematic studies in the future, to achieve consistent outcomes in a large-scale application.…”

Inhibitory Effects of Cu2O/SiO2 on the Growth of Microcystis aeruginosa and Its Mechanism

“…Treatment schemes for controlling HABs have focused on the physical, chemical, and biological methods [4][5][6]. Most of those methods show promise, but hard to achieve safe and efficient applications in natural water bodies.…”