Effect of 1.7 MHz ultrasound on a gas-vacuolate cyanobacterium and a gas-vacuole negative cyanobacterium

Biological activity and molecular mechanism of inactivation of Microcystis aeruginosa by ultrasound irradiation

Harmful algal blooms (HABs) significantly impact on water quality and ecological balance. Ultrasound irradiation has proven to be an effective method for algal control. Nevertheless, the molecular mechanisms underlying the inactivation of M. aeruginosa by ultrasound are still unknown. In this study, the physiological activity and molecular mechanism of algal cells exposed to different frequencies of ultrasound were studied. The results indicated a pronounced inhibition of algal cell growth by high-frequency, high-dose ultrasound. Moreover, with increasing ultrasound dosage, there was a higher percentage of algal cell membrane ruptures. SEM and TEM observed obvious disruptions in membrane structure and internal matrix. Hydroxyl radicals generated by high-frequency ultrasound inflicted substantial cell membrane damage, while increased antioxidant enzyme activities fortified cells against oxidative stress. Following 2 min of ultrasound irradiation at 740 kHz, significant differential gene expression occurred in various aspects, including energy metabolism, carbohydrate metabolism, and environmental information processing pathways. Moreover, ultrasound irradiation influenced DNA repair and cellular apoptosis, suggesting that the algal cells underwent biological stress to counteract the damage caused by ultrasound. These findings reveal that ultrasound irradiation inactivates algae by destroying their cell structures and metabolic pathways, thereby achieving the purpose of algal suppression.

Advances in the Formation and Control Methods of Undesirable Flavors in Fish

Undesirable flavor formation in fish is a dynamic biological process, decreasing the overall flavor quality of fish products and impeding the sale of fresh fish. This review extensively summarizes chemical compounds contributing to undesirable flavors and their sources or formation. Specifically, hexanal, heptanal, nonanal, 1−octen−3−ol, 1−penten−3−ol, (E,E)−2,4−heptadienal, (E,E)−2,4−decadienal, trimethylamine, dimethyl sulfide, 2−methyl−butanol, etc., are characteristic compounds causing off−odors. These volatile compounds are mainly generated via enzymatic reactions, lipid autoxidation, environmentally derived reactions, and microbial actions. A brief description of progress in existing deodorization methods for controlling undesirable flavors in fish, e.g., proper fermenting, defatting, appropriate use of food additives, and packaging, is also presented. Lastly, we propose a developmental method regarding the multifunctional natural active substances made available during fish processing or packaging, which hold great potential in controlling undesirable flavors in fish due to their safety and efficiency in deodorization.

Study on a novel omnidirectional ultrasonic cavitation removal system for Microcystis aeruginosa

Microcystis aeruginosa, as a typical alga, produces microcystin with strong liver toxicity, seriously endangering the liver health of human and animals. Inhibiting the bloom of the Microcystis aeruginosa in lakes becomes a significant and meaningful work. Ultrasonic cavitation is currently considered to be the most environmentally friendly and effective method for the removal of Microcystis aeruginosa. However, the commercialized ultrasonic algae removal systems require multi-Langevin transducers to achieve omnidirectional ultrasonic irradiation due to the single irradiation direction of the Langevin transducer, resulting in the complex design and high energy consumption. To achieve a low-cost, simple structure, and high-efficiency algae removal system, a novel omnidirectional ultrasonic cavitation removal system for Microcystis aeruginosa is proposed. The proposed system is major composed of a novel omnidirectional ultrasonic transducer, which generates the omnidirectional ultrasonic irradiation by its shaking-head motion coupled by two orthogonal bending vibration modes. Modal simulation, sound field simulation, and cavitation bubble radius simulation are first carried out to optimize the geometric sizes of the proposed transducer and verify the correctness of the omnidirectional ultrasonic irradiation principle. Then the vibration characteristics of the transducer prototype are measured by vibration tests and impedance tests. Finally, the feasibility and effectiveness of the proposed omnidirectional ultrasonic removal system for Microcystis aeruginosa are evaluated through the algae removal experiments. The experimental results exhibit that the algal cells damaged by ultrasonic irradiation from the proposed system do not have the ability to self-repair. In addition, the algal removal rates reached 55.41% and 72.97% after 30 min of ultrasonic treatment when the corresponding ultrasonic densities are 0.014 W/mL and 0.021 W/mL, respectively. The proposed omnidirectional ultrasonic algae removal system significantly simplifies the configuration and reduces energy consumption, presenting the potential promise of algae removal and environmental protection.

A critical review on operation and performance of source water control strategies for cyanobacterial blooms: Part II-mechanical and biological control methods

This review summarizes current knowledge on mechanical (artificial mixing, hypolimnetic aeration, dredging, and sonication) and biological (biomanipulation, macrophytes, and straws) methods for the management of cyanobacterial blooms in drinking water sources. Emphasis has been given to (i) the mechanism of cyanobacterial control, (ii) successful and unsuccessful case studies, and (iii) factors influencing successful implementation. Most mechanical and biological control strategies offer long-term control. However, their application can be cost-prohibitive and treatment efficacy is influenced by source water geometry and continual nutrient inputs from external sources. When artificial mixing and hypolimnetic oxygenation units are optimized based on source water characteristics, observed water quality benefits included increased dissolved oxygen contents, reduced internal loading of nutrients, and lower concentrations of reduced ions . Treatment efficacy during oxygenation and aeration was derailed by excessive sedimentation of organic matter and sediment characteristics such as low Fe/P ratios. Dredging is beneficial for contaminated sediment removal, but it is too costly to be a practical bloom control strategy for most systems. Sonication control methods have contradictory findings requiring further research to evaluate the efficacy and applicability for field-scale control of cyanobacteria. Biological control methods such as biomanipulation offer long-term treatment benefits; however, investigations on the mechanisms of field-scale cyanobacterial control are still limited, particularly with the use of macrophytes and straws. Each control method has site-specific strengths, limitations, and ecological impacts. Reduction of external nutrient inputs should still be a significant focus of restoration efforts as treatment benefits from mechanical and biological control were commonly offset by continued nutrient inputs.

Improved Cyanobacteria Removal from Harmful Algae Blooms by Two-Cycle, Low-Frequency, Low-Density, and Short-Duration Ultrasonic Radiation

Harmful algae blooms (HAB) in eutrophic lakes and rivers have become serious water quality problems that are difficult to eliminate using common methods. Previous research has demonstrated that powerful ultrasound can somewhat control cyanobacteria in HABs; however, effective and energy-efficient settings for ultrasonic parameters have not yet been rigorously determined. The results of this study showed that the effect of cyanobacteria removal was enhanced with ultrasonic frequencies, densities, and radiation durations of 20–90 kHz, 0.0005–0.1 W/mL and 0.5–10 min, respectively. Our analyses further demonstrated that the effective distance of ultrasound decreased with increasing frequency, and that damaged algae cells were able to repair themselves at low ultrasonic densities. To address the high energy consumption and small effective distance of conventional ultrasonic radiation treatments, we proposed a new cyanobacteria removal method based on two applications of low-frequency, low-density and short-duration ultrasonic radiation. We defined the energy effectiveness factors of ultrasonic radiation for algae removal as the algae removal rate divided by ultrasonic dosage. This method yielded an 87.6% cyanobacteria removal and the highest energy effectiveness factor, suggesting that two cycles of treatment provide a low-energy method for enhancing existing algae-removing technologies used in large bodies of water.

Microbial gas vesicles as nanotechnology tools: exploiting intracellular organelles for translational utility in biotechnology, medicine and the environment

A range of bacteria and archaea produce gas vesicles as a means to facilitate flotation. These gas vesicles have been purified from a number of species and their applications in biotechnology and medicine are reviewed here. Halobacterium sp. NRC-1 gas vesicles have been engineered to display antigens from eukaryotic, bacterial and viral pathogens. The ability of these recombinant nanoparticles to generate an immune response has been quantified both in vitro and in vivo. These gas vesicles, along with those purified from Anabaena flos-aquae and Bacillus megaterium, have been developed as an acoustic reporter system. This system utilizes the ability of gas vesicles to retain gas within a stable, rigid structure to produce contrast upon exposure to ultrasound. The susceptibility of gas vesicles to collapse when exposed to excess pressure has also been proposed as a biocontrol mechanism to disperse cyanobacterial blooms, providing an environmental function for these structures.

Ultrasonic Technology Applied against Mosquito Larvae

The effective management of mosquito vectors is a timely challenge for medical and veterinary entomology. In this study, we evaluated the acoustic Larvasonic device to control young instars of the mosquito Aedes aegypti in diverse freshwater environments. Under laboratory conditions, we investigated the effect of exposure time and distance from the transducer on the mortality of larvae and pupae of Ae. aegypti. Furthermore, we evaluated the effectiveness of the ultrasound window of the electromagnetic spectrum under different field conditions. Results showed that first and second instar larvae were more sensitive to the frequency range of 18–30 kHz of the Larvasonic device. Ultrasonic waves applied for 180 s at a frequency from 18 to 30 kHz caused 100% larval mortality at a distance of 60 cm from the transducer. No mortality was observed in the non-target copepod Megacyclops formosanus. The exposure to the soundwaves produced by the acoustic larvicidal device over different distances effectively damaged Ae. aegypti through destruction of the larval dorsal tracheal trunk, thorax and abdomen. Overall, results indicated that the Larvasonic device tested can provide an alternative tool to reduce young instar populations of Ae. aegypti, without any effects on non-target aquatic invertebrates like copepods. It turned out to be a useful device for mosquito biocontrol. This technology has a relevant potential to fight the spread of mosquito-borne diseases.

Study on ultrasonic treatment for degradation of Microcystins (MCs)

In recent years, The ecological environment of rivers and lakes have been seriously polluted, and the eutrophication of water bodies has become increasingly prominent, which not only seriously affects the living environment of surrounding residents, but also poses a major threat to the ecological security of water environment. The growth of algae is characterized by short cycle, rapid reproduction and great harmfulness. Conventional algal removal technology is expensive, easy to produce secondary pollution, and difficult to effectively inhibit algae outbreaks, therefore, a new environmental protection technology, ultrasonic algae removal technology, has been put forward. Under the background of ecological environment pollution, in this paper, the effect of ultrasonic technology on degradation of Microcystins (MCs) under different conditions and is investigated. Results show that Microcystins removal rate reaches 81% when Microcystin solution with a concentration of 12.43 mu/L is treated by ultrasound (1200 W) for 5 min; the removal rate of Microcystin reaches 99% after 15 min of ultrasound treatment (1200 W), and almost all of them are removed; no matter wastewater containing Microcystis is treated by ultrasound alone or ultrasound-coagulation method, the levels of Microcystins in the water do not increase. The results also prove that ultrasound can directly destroy the wall and kill algae, inhibit the growth activity of un-killed algae and degrade Microcystins. In addition, the technical principle and application prospect of ultrasonic algae removal instrument in ecological environment are introduced. The paper provided certain direction and theoretical support for the subsequent improvement of ultrasonic algae removal technology.

Effects of ultrasound on Microcystis aeruginosa cell destruction and release of intracellular organic matter

Harmful algal blooms negatively impact ecosystems and threaten drinking water sources. One potential method to effectively counteract algal blooms is ultrasonication. However, ultrasonication can easily lead to the release of intracellular organic matter (IOM). The purpose of this study was to investigate the relationship between the destruction of algal cells and IOM release at different ultrasound frequencies. Microcystis aeruginosa cells were ultrasonicated at 20 kHz with an intensity of 0.038 W/mL, 740 kHz with an intensity of 0.113 W/mL, and 1120 kHz with an intensity of 0.108 W/mL. The IOM release was detected by fluorescence spectroscopy in addition to the more commonly used haemocytometry and optical density. After ultrasonication for 15 min, the removal rate of algal cells reached 10.5% at 20 kHz, 9.46% at 740 kHz, and 35.4% at 1120 kHz. The 20 kHz and 740 kHz ultrasound caused local damage to algal cells and then disrupted them, whereas the 1120 kHz ultrasound directly disrupted most algal cells. The extracellular organic matter (EOM), which was increased by ultrasonication, mainly consisted of protein-like compounds, chlorophyll, and a small amount of humic-like substances. Gas vacuoles had been destructed before the cells were broken, as indicated by the decrease of cell size and the wrinkles on the cell surface. Moreover, the removal of algae cells while upholding integrity is more conducive to the safety of the water environment.

Enhanced coagulation by high-frequency ultrasound in Microcystis aeruginosa-laden water: Strategies and mechanisms

Ultrasonic treatment has attracted much attention because of its physical and chemical effects that are distinct from those of chemical agents. In particularly, high-frequency ultrasound is known as an effective method because the theoretical resonance frequency of the gas vesicles in Microcystis aeruginosa is in the high frequency range (>100 kHz), which causes gas vesicles collapse and changes the settleability of the algal cells. In this work, the effects of the ultrasonic frequency, acoustic power density and duration on enhancing coagulation to remove turbidity in algae-laden water were studied. In order to explain the mechanism, the morphology of algae cells, the changes in extracellular organic substances, the zeta potential and the formation of hydroxyl radicals were analyzed systematically. Finally, Zeta potentials and flocs morphology after adding PAC were investigated to verify the mechanism. The results showed that the frequency exhibited fewer effects than power and duration on coagulation. SEM images showed that there were more severe cellular damages at 430 and 740 kHz than other frequencies. Sonication could cause the collapse of gas vesicle inside the cell, which was due to the instantaneous high pressure generated by the ultrasonic cavitation instead of the resonance. Furthermore, sonication would result in an increase in proteins in extracellular organic matter (EOM) with continuous ultrasonic irradiation, indicating that a small amount of proteins could promote coagulation and that the accumulation of proteins would inhibit coagulation. Free radical content testing showed that the production of excessive free radicals was often accompanied by a deterioration of the coagulation. The proper mechanical effects were the main mechanism of ultrasonic enhanced coagulation. Thus, it was recommended that the appropriate ultrasonic condition was the one that resulted in a small amount of protein leakage and little generation of free radicals, which occurred at 740 kHz and 0.02 W/mL in approximately 5 min, and would significantly enhance the turbidity removal rate in algae-containing water from approximately 80-90%.

Variation of efficiencies and limits of ultrasonication for practical algal bloom control in fields

Algal blooms are an increasing issue in managing water resources for drinking water production and recreational activities in many countries. Among various techniques, ultrasonication is known as a cost-effective method for control of harmful algal blooms (HABs) in relatively large area of water bodies. Most of engineering parameters for operating ultrasonication have been empirically determined based on laboratory scale tests, however, field or pilot tests in real environments are still rare. For field application, duration of ultrasonication is often on a monthly basis which is impractical for stream where there is flow and thus retention time is short. More realistic experimental approaches are required for practical applications of ultrasound. In this study, relatively low frequencies (36-175 kHz) of ultrasonication with low power intensity, less than 650 W, were tested for algal control in various pilot (100-750 L) and field (4 m³) tests in a short duration (<20 min). Generally, rapid decline of sound pressure (Pa) of ultrasonication was observed with distance (80% decrease even with 0.5 m difference). In a pilot test (100 L), the highest algae reduction was achieved at 36 kHz with 0.003 W mL^-1 of power density within 10 min duration, but there was a noticeable increase in microcystin due to damaged algal cells by the low frequency of ultrasound. In a short-term operation without flow, distance from the ultrasound system was an important parameter for effective algae reduction, while longer exposure time ensured sufficient algae reduction. In a circulation pond (4 m³) with flow, 108 kHz-450 W showed the greatest efficiency in algal control and approximately 50-90% algal cells reduction was observed at 36-175 kHz with less than 650 W power and 60 min duration.

Inhibition of the photosynthetic activity of Synedra sp. by sonication: Performance and mechanism

The impacts of sonication on the photosynthetic activity of Synedra sp. (diatom) and its mechanism were investigated for the first time. Three photosynthetic parameters, i.e., effective quantum yield (Φ_e), initial slope of rapid light curves (α) and maximum relative electron transport rate (rETR_max) were employed to evaluate its photosynthetic activity during sonication for the first time. The results showed that 600 kHz is the optimal frequency for the inhibition of the photosynthetic activity and biomass as the ultrasonic frequencies varied from 100 to 800 kHz. When the photosynthetic activity was inhibited to be not detected by sonication, Φ_e, α and rETR_max gradually recovered from 0 to 36.4%, 35.2% and 48.3% of that in the blank group, respectively, after 12-day cultivation (no sonication). However, the biomass was still suppressed to 9.2% of that in the blank after the same cultivation. A single time sonication treatment achieved better inhibition efficiency than the multiple times modes when their total sonication time was equal. The inhibition mechanism for the photosynthetic activity of Synedra sp. by sonication can be concluded as follows: at the early stage, the thylakoids membrane expansion and oscillation can lead to the structure damage of thylakoids; subsequently, OH oxidation is responsible for the chlorophyll-a degradation.

Effects of Low-Frequency Ultrasound on Microcystis aeruginosa from Cell Inactivation to Disruption

Ultrasound can be used to induce cell resonance and cavitation to inhibit cyanobacterial growth, but it can also lead to increase in dissolved nutrients because of cell disruption. This study investigated the process from cell inactivation to disruption of Microcystis aeruginosa. Algal cells were sonicated (at 35 kHz) under various intensities and durations. Results showed that chlorophyll a content and F_v/F_m values decreased slightly within the first 5 min. Superoxide dismutase activity was stimulated and its peak value appeared at the fifth minute. After 20 min, considerable number of ruptured cells were observed and the concentrations of dissolved nitrogen and phosphorus increased rapidly. Finally, ammonia and nitrate merely composed a small portion of dissolved nitrogen. This study demonstrated that excessive ultrasound treatment can significantly rupture algal cells and lead to the release of cellular inclusions, which may cause ecological issues or public health problems. Based on our findings, ultrasonic intensity controlled at 0.035 W/mL and applied for a duration of 20 min delivers the optimal result in effectively inhibiting physiological activities of Microcystis aeruginosa without marked cell disruption. This will ultimately help to achieve algal control, while conserving energy and preserving the environment and human health.

Comparison of Four Quantitative Techniques for Monitoring Microalgae Disruption by Low-Frequency Ultrasound and Acoustic Energy Efficiency

Ultrasound has been regarded as an environmental friendly technology to utilize microalgae biomass and control algal blooms. In this study, four quantitative techniques, including cell counting, optical density of algal suspension, pigments release, and protein release, were performed on three species of microalgae ( M. aeruginosa, C. pyrenoidosa, and C. reinhardtii) to develop effective techniques for rapid monitoring of cell disruption and to optimize the acoustic energy efficiency. Results showed optical density of algal suspensions was not an optimal indicator to monitor cell disruption, although it is a common technique for determining cell concentration in microbial cultures. Instead, an accurate and reliable technique was to determine the release of intracellular pigments (absorbance peaks of supernatant) for indicating cell rupture. The protein released during sonication could also be a useful indicator if it is the component of interest. A fitted power functional model showed a strong relationship between cell disruption and energy consumption ( R² > 0.87). This model could provide an effective approach to directly compare the energy efficiency of ultrasound in different systems or with varying microalgae species. This study provides valuable information for microalgae utilization and the treatment of algal blooms by ultrasound, so as to achieve energy conservation and environmental safety.

Ultrasonic selectivity on depressing photosynthesis of cyanobacteria and green algae probed by chlorophyll-a fluorescence transient

Ultrasound can inhibit cyanobacterial growth through rupturing cells, but this pathway frequently has the risk to release intercellular toxin (e.g., microcystin). Depressing photosynthesis without cell disruption may provide a new strategy to control cyanobacterial blooms using ultrasound, especially Microcystis blooms. In this work, Microcystis aeruginosa (toxic cyanobacteria) and Chlorella pyrenoidosa (typical green algae) were chosen as model microalgae to verify this hypothesis. Results showed that ultrasound has the ability to inhibit cyanobacterial photosynthesis significantly and selectively. Specifically, sonication damaged Q_A, a tightly bound one-electron acceptor, and blocked electron flow at Q_B, a two-electron acceptor, in the photosystem II (PSII) of M. aeruginosa when it was exposed for 60 s (35 kHz, 0.043 W/cm³). Moreover, 44.8% of the reaction centers (RCs) in the PSII of M. aeruginosa were transferred into inactive ones (RC^sis), and the cell concentration decreased by 32.5% after sonication for 300 s. By contrast, only 7.9% of RC^si occurred in C. pyrenoidosa, and cell concentration and chlorophyll-a content reduced by 18.7% and 9.3%, respectively. Differences in both species (i.e., cell structures) might be responsible for the varying levels to sonication. This research suggests that cyanobacteria, especially Microcystis, could be controlled by ultrasound via damaging their PSIIs.

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

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.

Long alkyl-chain imidazolium ionic liquids: Antibiofilm activity against phototrophic biofilms

Biofilm formation is problematic and hence undesirable in medical and industrial settings. In addition to bacteria, phototrophic organisms are an integral component of biofilms that develop on surfaces immersed in natural waters. 1-Alkyl-3-methyl imidazolium ionic liquids (IL) with varying alkyl chain length were evaluated for their influence on the formation of monospecies (Navicula sp.) and multispecies biofilms under phototrophic conditions. An IL with a long alkyl side chain, 1-hexadecyl-3-methylimidaazolium chloride ([C₁₆(MIM)][Cl]) retarded growth, adhesion and biofilm formation of Navicula sp. at concentrations as low as 5μM. Interestingly, [C₁₆(MIM)][Cl] was very effective in preventing multispecies phototrophic biofilms on fibre reinforced plastic surfaces immersed in natural waters (fresh and seawater). SYTOX^® Green staining and chlorophyll leakage assay confirmed that the biocidal activity of the IL was exerted through cell membrane disruption. The data show that [C₁₆(MIM)][Cl] is a potent inhibitor of phototrophic biofilms at micromolar concentrations and a promising agent for biofilm control in re-circulating cooling water systems. This is the first report that ionic liquids inhibit biofilm formation by phototrophic organisms which are important members of biofilms in streams and cooling towers.

A review on acoustic methods of algal growth control by ultrasonication through existing and novel emerging technologies

The uncontrolled proliferation of algae and algal blooms due to excessive nutrient loading in natural and industrial water bodies is a major issue for water quality maintenance. It reduces usability of the water, imposes hazardous effects of algal toxins released from algal blooms, and creates nuisance in the operation of several industrial water units. Among several existing water treatment methods to diminish the post-algae growth effects, ultrasonication has emerged as an environmentally safe technology that does not involve any use of algaecide. The interaction of several parameters, including climatic and environmental conditions with algae growth rate, have been reviewed in this article. The effects of different acoustic operating conditions for inhibition of algae growth have also been discussed. Concern about high energy consumption led other technologies to be integrated with ultrasonication. It has enhanced the process efficiency and reduced the energy consumption as reported in some long-term field investigations and patent proposals. Several issues that require further research for making this technology widely applicable or to install an effective system design have been highlighted in this article.

Beneficial changes in biomass and lipid of microalgae Anabaena variabilis facing the ultrasonic stress environment

This study investigated the beneficial effects of ultrasonic treatment on the biomass, lipid and protein of the microalgae Anabaena variabilis. The microalgae after 11days cultivation (initial algae) were treated at the powers of 200, 350 and 500W for 10min and then cultured continuously for 3days (day 12-14). The power of 200W induced the highest lipid content 37.8% on day 12. The subsequent experiments tested the ultrasonic treatment times of 5, 10, 20 and 40min at 200W in the initial algae. The significantly improved lipid content 46.9% and productivity 54.2mg/L/d were obtained almost 1.46 and 1.86times more than that of the control algae respectively after 1day of continuous cultivation at 5min. The proper ultrasonic treatment showed the feasibility and high efficiency in promoting lipid accumulation without negatively influencing the biomass, fatty acid profiles and protein content.

Toxic cyanobacteria and drinking water: Impacts, detection, and treatment

Blooms of toxic cyanobacteria in water supply systems are a global issue affecting water supplies on every major continent except Antarctica. The occurrence of toxic cyanobacteria in freshwater is increasing in both frequency and distribution. The protection of water supplies has therefore become increasingly more challenging. To reduce the risk from toxic cyanobacterial blooms in drinking water, a multi-barrier approach is needed, consisting of prevention, source control, treatment optimization, and monitoring. In this paper, current research on some of the critical elements of this multi-barrier approach are reviewed and synthesized, with an emphasis on the effectiveness of water treatment technologies for removing cyanobacteria and related toxic compounds. This paper synthesizes and updates a number of previous review articles on various aspects of this multi-barrier approach in order to provide a holistic resource for researchers, water managers and engineers, as well as water treatment plant operators.

Modeling bubble dynamics and radical kinetics in ultrasound induced microalgal cell disruption

Microalgal cell disruption induced by acoustic cavitation was simulated through solving the bubble dynamics in an acoustical field and their radial kinetics (chemical kinetics of radical species) occurring in the bubble during its oscillation, as well as calculating the bubble wall pressure at the collapse point. Modeling results indicated that increasing ultrasonic intensity led to a substantial increase in the number of bubbles formed during acoustic cavitation, however, the pressure generated when the bubbles collapsed decreased. Therefore, cumulative collapse pressure (CCP) of bubbles was used to quantify acoustic disruption of a freshwater alga, Scenedesmus dimorphus, and a marine alga, Nannochloropsis oculata and compare with experimental results. The strong correlations between CCP and the intracellular lipid fluorescence density, chlorophyll-a fluorescence density, and cell particle/debris concentration were found, which suggests that the developed models could accurately predict acoustic cell disruption, and can be utilized in the scale up and optimization of the process.

Microalgal cell disruption in a high-power ultrasonic flow system

A 2-kW continuous ultrasonic flow system (UFS) was found effective in the disruption of two microalgal strains: Scenedesmus dimorphus and Nannochloropsis oculata. Compared to the control, cell debris concentration of UFS treatments increased up to 202% for S. dimorphus and 112% for N. oculata. Similarly, Nile red stained lipid fluorescence density (NRSLD) increased up to 59.5% and 56.3% for S. dimorphus and N. oculata, respectively. It was also found that increasing ultrasound intensity improved cell disruption efficiency indicated by up to 54% increase in NRSLFD of the two strains. Increasing sonication-processing time to 3-min resulted in 33.0% increase for S. dimorphus and 45.7% increase for N. oculata in NRSLFD compared to the control. Cell recirculation was found beneficial to cell disruption, however, higher initial cell concentration significantly reduced cell disruption efficiency, indicated by 98.2% decrease in NRSLFD per cell when initial cell concentration increased from 4.25 × 10(6) to 1.7 × 10(7)cells ml(-1).

Beating the blues: is there any music in fighting cyanobacteria with ultrasound?

The hypothesis that cyanobacteria can be controlled by commercially available ultrasound transducers was tested in laboratory experiments with cultures of the cyanobacteria Anabaena sp., Cylindrospermopsis raciborskii and Microcystis aeruginosa and the green alga Scenedesmus obliquus that were grown in the absence or presence of ultrasound (mix of 20, 28 and 44 kHz). The Scenedesmus experiment also included a treatment with the zooplankton grazer Daphnia magna. Chlorophyll-a and biovolume-based growth of Anabaena was significantly lower in ultrasound exposed cultures than in controls. Particle based growth rates were higher in ultrasound treatments. Filaments were significantly shorter in ultrasound exposed cultures reflecting filament breakage. Photosystem II efficiency was not affected by ultrasound. In Cylindrospermopsis chlorophyll-a based growth rates and photosystem II efficiencies were similar in controls and ultrasound treatments, but biovolume-based growth was significantly lower in ultrasound exposed cultures compared to controls. Despite biovolume growth rates of the filamentous cyanobacteria were reduced in ultrasound treatments compared to controls, growth remained positive implying still a population increase. In Microcystis and Scenedesmus growth rates were similar in controls and ultrasound treatments. Hence, no effect of ultrasound on these phytoplankton species was found. Ultrasound should not be viewed "environmental friendly" as it killed all Daphnia within 15 min, releasing Scenedesmus from grazing control in the cultures. Based on our experiments and critical literature review, we conclude that there is no music in controlling cyanobacteria in situ with the commercially available ultrasound transducers we have tested.

Cyanotoxin management and human health risk mitigation in recreational waters

The occurrence and severity of harmful cyanobacterial or blue-green algal blooms (HABs) have increased in recent decades, posing a serious threat of illness to humans. In some countries, water contaminated with cyanotoxins that is used for drinking or haemodialysis has posed a particularly serious risk. However, it is now recognized that recreational exposure to natural toxins by skin contact, accidental swallowing of water or inhalation can also cause a wide range of acute or chronic illnesses. In this review, we focus on the importance of cyanotoxin management in recreational waters. The symptoms related with HAB poisonings, the recommended safety concentrations limit for cyanobacteria and cyanotoxins in such waters, as well as early health hazard indicators of their presence and their monitoring are all discussed. We also present in this review an overview of the methods developed in recent decades for eliminating cyanobacteria and the toxic compounds that they produce.

Quantification of the ultrasound induced sedimentation of Microcystis aeruginosa

It has been known for more than 40 years that vacuolate organisms can be induced to sediment with ultrasound. However, robust indicators are still needed to compare the efficacy of different treatments. A repeatable index is proposed that makes it possible to quantify the ultrasonic induced sedimentation. The procedure is used to monitor the long term sedimentation of Microcystis aeruginosa after sonication. Results reveal that the sedimentation process continues after gas vesicles have fully recovered, although at a slower rate.

The influence of ultrasound frequency and power, on the algal species Microcystis aeruginosa, Aphanizomenon flos-aquae, Scenedesmus subspicatus and Melosira sp

We report on the effectiveness of sonication on controlling the growth of four problematic algal species which are morphologically different and from three algal divisions. Two cyanobacterial species Microcystis aeruginosa (unicellular) and Aphanizomenon flos-aquae (filamentous), one green alga Scenedesmus subspicatus (colonial) and lastly a diatom species Melosira sp. (filamentous) were subjected to ultrasound of selected low to high frequencies ranging from 20 to 1144 kHz. Microcystis aeruginosa and Scenedesmus subspicatus highest cell removal rates were 16 +/- 2% and 20 +/- 3% when treated with the same ultrasound frequency of 862 kHz but differing energy levels of 133 and 67 kWh m(-3), respectively. Aphanizomenon flos-aquae best removal rate was 99 +/- 1% after 862 kHz and 133 kWh m(-3) of energy, with Melosira sp. achieving its highest cell removal at 83% subsequent to ultrasound of 20 kHz and 19 kWh m(-3). Microcystis aeruginosa and Scenedesmus subspicatus are considered non-susceptible species to ultrasound treatment from a water treatment perspective due to their low cell removal rates; however, photosynthetic activity reduction of 65% for Microcystis aeruginosa does indicate the possible utilization of ultrasound to control bloom growth, rather than bloom elimination. Conversely, Aphanizomenon flos-aquae and Melosira sp. are deemed species highly susceptible to ultrasound. Morphological differences in shape (filamentous/non-filamentous) and cell wall structure (silica/peptidoglycan), and presence of gas vacuoles are probable reasons for these differing levels of susceptibility to ultrasound.

Removal of blue-green algae using the hybrid method of hydrodynamic cavitation and ozonation

A suspension of Microcystis aeruginosa (30 μg L(-1)chlorophyll a) was circulated in a hydrodynamic cavitation device and ozone was introduced at the suction side of the pump. The removal of algae over 10 min using hydrodynamic cavitation alone and ozone alone is less than 15% and 35%, respectively. The destruction of algae rises significantly from 24% in the absence of the orifice to 91% with the optimized orifice on 5 min of processing using hydrodynamic cavitation along with ozone (HC/O(3)) and the utilization of ozone increases from 32% to 61%. Interestingly, the suction process is more effective than the extrusion method (positive pressure) and the optimal bulk temperature for algal elimination was found to be 20 °C. Increasing the input concentration of ozone is favorable for the removal of algae but leads to a greater loss of ozone and a decrease in the utilization of ozone. Under the optimal conditions, the algal cells and chlorophyll a are completely destroyed in 10 min by use of the hybrid method.

A review of the use of sonication to control cyanobacterial blooms

The development of cyanobacterial blooms in water bodies imparts undesirable characteristics to the water such as odours, tastes and the potential presence of toxins. Several chemical and physical methods have been used to control the blooms, but have limitations in terms of pollution and application on a large scale. A more recent approach has been the use of sonication in the control of cyanobacteria (also referred to as blue-green algae). This paper reviews current advancements in research on using sonication to control cyanobacteria, particularly Microcystis aeruginosa, as it is a prevalent and a major bloom-forming toxic species. The impact of sonication on the structure and function of M. aeruginosa is discussed, including the influence of sonication parameters such as power intensity, frequency and exposure time. Alternate strategies of cyanobacterial control in combination with sonication are also reviewed.

Evaluation of the mechanisms of the effect of ultrasound on Microcystis aeruginosa at different ultrasonic frequencies

Blooms of cyanobacteria are now considered to be a common environmental issue. They are hazardous to both domestic and wild animals and humans. Current treatments are unable to effectively control such blooms as they become tolerant to biocides and it is difficult to degrade cyanobacterial toxins in water. Alternative methods for control are currently under investigation. One potential effective method is ultrasonic irradiation. Ultrasound inactivates algal and cyanobacteria cells through cavitation by generating extreme conditions, resulting in a number of physical, mechanical and chemical effects. The aim of this study was to investigate the effect of ultrasound at different frequencies on Microcystis aeruginosa. Flow cytometry was used to measure cyanobacterial metabolic cell viability in addition to the more commonly used haemocytometry, optical density and fluorimetry. Results indicate low frequency 20 kHz ultrasound with high intensity (0.0403 W cm(-3)) is effective for the inactivation of cyanobacterial cells. Higher frequencies of 580 kHz (0.0041 W cm(-3)) also resulted in an inactivation effect, but 1146 kHz (0.0018 W cm(-3)) showed a declumping effect as evidenced by flow cytometry. Ultrasonic treatment over time under different sonication conditions demonstrates the following: 1. Acoustic cavitation via mechanical effects can induce sufficient shear forces to directly rupture cyanobacteria cells. 2. At higher ultrasonic frequencies the mechanical energy of cavitation is less but a larger proportion of free radicals are produced from the ultrasonic degradation of water, which chemically attacks and weakens the cyanobacteria cell walls. 3. At higher frequencies free radicals also damage chlorophyll a leading to a loss in photosynthetic cell viability. 4. At low powers ultrasonic energy results in declumping of cyanobacteria.

Impact of sonication at 20 kHz on Microcystis aeruginosa, Anabaena circinalis and Chlorella sp

Blooms of toxic cyanobacteria such as Microcystis aeruginosa periodically occur within wastewater treatment lagoons in the warmer months, and may consequently cause contamination of downstream water and outages of the supply of recycled wastewater. Lab-scale sonication (20 kHz) was conducted on suspensions of M. aeruginosa isolated from a wastewater treatment lagoon, and two other algal strains, Anabaena circinalis and Chlorella sp., to investigate cell reduction, growth inhibition, release of microcystin and sonication efficiency in controlling the growth of the M. aeruginosa. For M. aeruginosa, for all sonication intensities and exposure times trialled, sonication led to an immediate reduction in the population, the highest reduction rate occurring within the initial 5 min. Sonication for 5 min at 0.32 W/mL, or for a longer exposure time (>10 min) at a lower power intensity (0.043 W/mL), led to an immediate increase in microcystin level in the treated suspensions. However, prolonged exposure (>10 min) to sonication at higher power intensities reduced the microcystin concentration significantly. Under the same sonication conditions, the order of decreasing growth inhibition of the three algal species was: A. circinalis > M. aeruginosa > Chlorella sp., demonstrating sonication has the potential to selectively remove/deactivate harmful cyanobacteria from the algal communities in wastewater treatment lagoons.

Optimization of Chlorella pyrenoidosa Removal by Low Frequency Ultrasonic Irradiation Using Response Surface Design

The control parameters of the removal of Chlorella pyrenoidosa, which was irradiated by low frequency ultrasonic, is optimized by using single factor experiments and response surface methodology (RSM). First of all, the approximate ranges of the ultrasonic frequency, the ultrasonic power and the irradiation time were estimated with single factor experiments for the further experiments. And then the optimized values of the three control parameters were determined, which were analyzed by using central composite design (CCD) and RSM. The results showed that the removal rate of chlorophyll-a could reach to 64.1% after the irradiation for 6.34min by using ultrasonic of 77.7 kHz and 250W. Ultrasonic technology can remove Chlorella pyrenoidosa cells in water quickly and effectively, so as to achieve the purpose of water purification.

Ultrasound effects on the antioxidative defense systems of Porphyridium cruentum

Ultrasound is a special physical stimulus that has a variety of biological effects. This study provides a first systemic investigation on the ultrasound-induced oxidation and protection actions of the antioxidant defense system in Porphyridium cruentum. The hydroxyl radical and superoxide anion radical scavenging ability of the cells and the electrolyte leakage of the cell membrane were examined. The change of glutathione and carotenoids produced with/without ultrasonic processing were measured; the enzyme activities of superoxide dismutase, catalase, and membrane bound ATPases (Na(+)/K(+)-ATPase, Ca(2+)/Mg(2+)-ATPase) were evaluated for either ultrasound-treated or untreated P. cruentum. The hydroxyl radical and superoxide anion radical scavenging ability of ultrasound-treated P. cruentum increase 49.8 and 76.0%, respectively, of which the electrolyte leakage and malonyldialdehyde accumulation are also found increased 48.6 and 48.0%, respectively, indicating a state of oxidative stress. A significant enhancement of the activities of superoxide dismutase by 53.5%, catalase, membrane bound ATPases (Na(+)/K(+)-ATPase, Ca(2+)/Mg(2+)-ATPase increased by 67.7 and 69.3%, respectively), and the increment of glutathione and carotenoids production are also observed. These results suggested that oxidative stress manifested by elevated reactive oxygen species levels and malonyldialdehyde contents might be resulted from the biophysical responses of P. cruentum to the physical stimuli, and most likely the enhanced antioxidation ability of the algal cells stimuli by ultrasonic comes from the enhancement of enzymatic and nonenzymatic preventive substances as observed in this work.