An investigation of mechanisms for the enhanced coagulation removal of Microcystis aeruginosa by low-frequency ultrasound under different ultrasound energy densities

• Published in: Ultrasonics sonochemistry Vol. 69; p. 105278
• Main Authors: Huang, Yang-Rui, Li, Lei, Wei, Xin-Min, Li, Huai-Zheng, Zeng, Juan-Yan, Kuang, Rui
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.12.2020
• Subjects: Algal organic matter; Biofouling; Chemical Precipitation; Coagulation; Energy density; Low-frequency ultrasound; Mechanisms; Microcystis; Ultrasonics; Water Purification - methods; Energy density; Mechanisms; Algal organic matter; Low-frequency ultrasound; Coagulation
• ISSN: 1350-4177; 1873-2828
• DOI: 10.1016/j.ultsonch.2020.105278

[Display omitted] •Coagulation removal is improved by a short amount of ultrasound (29.4 kHz, 0.6–2.22 J/mL)•Ultrasound (29.4 kHz) with an energy density higher than 0.6 J/mL reduces cell activity.•Ultrasound (29.4 kHz) with an energy density higher than 1.11 J/mL causes cell aggregation.•Ultrasound (29.4 kHz) with a very high energy (≥18 J/mL) density may impair water quality. There is a lack of studies elaborating the differences in mechanisms of low-frequency ultrasound-enhanced coagulation for algae removal among different ultrasound energy densities, which are essential to optimizing the economy of the ultrasound technology for practical application. The performance and mechanisms of low-frequency ultrasound (29.4 kHz, horn type, maximum output amplitude = 10 μm) -coagulation process in removing a typical species of cyanobacteria, Microcystis aeruginosa, at different ultrasound energy densities were studied based on a set of comprehensive characterization approaches. The turbidity removal ratio of coagulation (with polymeric aluminum salt coagulant at a dosage of 4 mg Al/L) was considerably increased from 44.1% to 59.7%, 67.0%, and 74.9% with 30 s of ultrasonic pretreatment at energy densities of 0.6, 1.11, and 2.22 J/mL, respectively, indicating that low-frequency ultrasound-coagulation is a potential alternative to effectively control unexpected blooms of M. aeruginosa. However, the energy density of ultrasound should be deliberately considered because a high energy density (≥18 J/mL) results in a significant release of algal organic matter, which may threaten water quality security. The specific mechanisms for the enhanced coagulation removal by low-frequency ultrasonic pretreatment under different energy densities can be summarized as the reduction of cell activity (energy density ≥ 0.6 J/mL), the slight release of negatively charged algal organic matter from cells (energy density ≥ 1.11 J/mL), and the aggregation of M. aeruginosa cells (energy density ≥ 1.11 J/mL). This study provides new insights for the ongoing study of ultrasonic pretreatment for the removal of algae via coagulation.