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

Comprehensive strategies for microcystin degradation: A review of the physical, chemical, and biological methods and genetic engineering

Addressing the threat of harmful cyanobacterial blooms (CyanoHABs) and their associated microcystins (MCs) is crucial for global drinking water safety. In this review, we comprehensively analyze and compares the physical, chemical, and biological methods and genetic engineering for MCs degradation in aquatic environments. Physical methods, such as UV treatments and photocatalytic reactions, have a high efficiency in breaking down MCs, with the potential for further enhancement in performance and reduction of hazardous byproducts. Chemical treatments using chlorine dioxide and potassium permanganate can reduce MC levels but require careful dosage management to avoid toxic by-products and protect aquatic ecosystems. Biological methods, including microbial degradation and phytoremediation techniques, show promise for the biodegradation of MCs, offering reduced environmental impact and increased sustainability. Genetic engineering, such as immobilization of microcystinase A (MlrA) in Escherichia coli and its expression in Synechocystis sp., has proven effective in decomposing MCs such as MC-LR. However, challenges related to specific environmental conditions such as temperature variations, pH levels, presence of other contaminants, nutrient availability, oxygen levels, and light exposure, as well as scalability of biological systems, necessitate further exploration. We provide a comprehensive evaluation of MCs degradation techniques, delving into their practicality, assessing the environmental impacts, and scrutinizing their efficiency to offer crucial insights into the multifaceted nature of these methods in various environmental contexts. The integration of various methodologies to enhance degradation efficiency is vital in the field of water safety, underscoring the need for ongoing innovation.

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.

Enhancing the growth of thermophilic Bacillus licheniformis YYC4 by low-intensity fixed-frequency continuous ultrasound

The effect of low-intensity fixed-frequency continuous ultrasound (LIFFCU) on the growth of Bacillus licheniformis YYC4 was investigated. The changes in morphology and activity of the organism, contributing to the growth were also explored. Compared with the control, a significant increase (48.95%) in the biomass of B. licheniformis YYC4 (at the logarithmic metaphase) was observed following the LIFFCU (28 kHz, 1.5 h and 120 W (equivalent to power density of 40 W/L)) treatment. SEM images showed that ultrasonication caused sonoporation, resulting in increased membrane permeability, evidenced by increase in cellular membrane potential, electrical conductivity of the culture, extracellular protein and nucleic acid, and intracellular Ca2+ content. Furthermore, LIFFCU action remarkably increased the extracellular protease activity, volatile components of the culture medium, microbial metabolic activity, and spore germination of the strain. Therefore, LIFFCU could be used to efficiently promote the growth of targeted microorganisms.

Neglected methane production and toxicity risk in low-frequency ultrasound for controlling harmful algal blooms

Algal blooms are regarded as a significant source of CH₄ emissions. Ultrasound has been gradually employed as a fast and efficient algae removal technology in recent years. However, the changes in water environment and potential ecological effects caused by ultrasonic algae removal are not fully clear. Here, a 40-day microcosm study was performed to simulate the collapse of Microcystis aeruginosa blooms after ultrasonic treatment. The results showed that low-frequency ultrasound at 29.4 kHz for 15 min removed 33.49% of M. aeruginosa and contributed to the destruction of cell structure, but it intensified the leakage of intracellular algal organic matter and microcystins. The accelerated collapse of M. aeruginosa blooms after ultrasonication promoted the rapid formation of anaerobic and reductive methanogenesis conditions, and elevated dissolved organic carbon content. Moreover, the release of labile organics, including tyrosine, tryptophan, protein-like compositions, and aromatic proteins, was facilitated by the collapse of M. aeruginosa blooms after ultrasonic treatment, and they supported the growth of anaerobic fermentation bacteria and hydrogenotrophic Methanobacteriales. This was also demonstrated by the increase in methyl-coenzyme M reductase (mcrA) genes in sonicated algae added treatments at the end of incubation. Finally, the CH₄ production in sonicated algae added treatments was 1.43-fold higher than that in non-sonicated algae added treatments. These observations suggested that ultrasound for algal bloom control potentially increased the toxicity of treated water and its greenhouse gas emissions. This study can provide new insights and guidance to evaluate environmental effects of ultrasonic algae removal.

Effect of Sonication on Microwave Inactivation Kinetics of Enterococcus faecalis in Dairy Effluent

The aim of this study is to inactivate Enterococcus faecalis ATCC 29212 present in dairy wastewater effluent using microwave (MW) waves and/or ultrasound waves (US). The ultrasonic bath treatment (35 kHz) had no significant effect on the reduction of the survival rate (predominant declumping effect). At 650 W of microwave treatment, the total destruction was completed at 75 s, while at 350 W a 3 log reduction was achieved. The Weibull model was fitted to the survival curves to describe the inactivation kinetics, and the effect of the combined microwave-ultrasound treatments was evaluated. The scaling parameter α that was estimated from the inactivation kinetics for the microwaves combined with the ultrasound waves in pre-treatment was found to be lower than the scaling parameters obtained in post-treatment, which were in turn lower than those estimated for microwaves or ultrasound waves alone. The use of the ultrasound waves in pre-treatment was more effective than in post-treatment; a total reduction was achieved using a combination of US (30 min) followed by MW (650 W) with α = 28.3 s, while 4.0 log was obtained by reversing all processes with α = 34.5 s. The results from the protein assays indicate that the bacterial wall was damaged and that holes were formed from which protein leakage occurred.

Low-frequency ultrasound and nitrogen limitation induced enhancement in biomass production and lipid accumulation of Tetradesmus obliquus FACHB-12

The two-stage cultivation strategy was optimized in this study to simultaneously promote the growth and lipid accumulation of Tetradesmus obliquus. Results showed that the optimal dual-stress conditions were nitrogen concentration at 25 mg N·L^-1 and low-frequency ultrasound at 200 Watt, 1 min, and 8 h interval. The biomass and lipid content of Tetradesmus obliquus were increased by 32.1% and 44.5%, respectively, comparing to the control, and the lipid productivity reached 86.97 mg^-1·L^-1·d^-1 at the end of the cultivation period. The protein and photosynthetic pigment contents of microalgae decreased by 22.4% and 14.0% under dual stress comparing to the control environment. In addition, dual stress cultivation of microalgae presented higher level of antioxidant capacity to balance to oxidation level in microalgal cells. This study provides a new insight for microalgae growth and lipid accumulation with dual stress stimulation.

Design, synthesis, high algicidal potency, and putative mode of action of new 2-cyclopropyl-4-aminopyrimidine hydrazones

Control of cyanobacteria harmful algal blooms remains a global challenge. In the present study, a series of novel 2-cyclopropyl-4-aminopyrimidine hydrazones were designed and synthesized as potential algicides. Compounds 4a, 4b, 4h, 4j, 4k, 4l, and 4m showed potent inhibition against Synechocystis sp. PCC6803 (median effective concentration, EC₅₀ = 1.1 to 1.7 μM) and Microcystis aeruginosa FACHB905 (EC₅₀ = 1.2 to 2.0 μM), more potent than, or comparably with, copper sulfate (PCC6803, EC₅₀ = 1.8 μM; FACHB905, EC₅₀ = 2.2 μM) and prometryne (PCC6803, EC₅₀ = 12.3 μM; FACHB905, EC₅₀ = 7.2 μM). Compound 4k exhibited algicidal activity in an expanded culture system, and was less toxic than copper sulfate to zebrafish. Electron microscope analyses showed that 4k damaged cyanobacterial cells and decreased the number of thylakoid lamellae. Transcriptomic and qPCR analyses suggest that 4k interfered photosynthesis-related pathways. Treatment with 4k significantly decreased the maximum quantum yield of photosystem II and the photosynthetic electron transfer rate, and the resulting reactive oxygen species damaged thylakoid membranes and photosystem I. The results suggest that 4k is a potential lead for further development of effective and safe algicides.

Oxidative stress of Microcystis aeruginosa induced by algicidal bacterium Stenotrophomonas sp. KT48

Cyanobacterial harmful algal blooms are a worldwide problem with substantial adverse effects on the aquatic environment as well as human health. Among the multiple physicochemical and biotic approaches, algicidal bacterium is one of the most promising and eco-friendly ways to control bloom expansion. In this study, Stenotrophomonas sp. KT48 isolated from the pond where cyanobacterial blooms occurred exhibited a strong inhibitory effect on Microcystis aeruginosa. However, the algicidal performance and mechanisms of Stenotrophomonas sp. remain under-documented. To explore the algicidal performance and physiological response againt M. aeruginosa, further works were implemented here. Our results indicated that the algicidal rate of strain KT48 cultured in 1/8 LB medium supplemented with 0.3% starch or glucose was about 30% higher than that in 1/8 LB medium. Strain KT48 culture, cell-free filtrate, and cells re-suspended were inoculated into the M. aeruginosa culture, and the Chl-a content was determined. Those results indicated that the algicidal activity of cells re-suspended was far higher than that of cell-free filtrate and culture. Thus, strain KT48 exhibited algicidal activity mainly through direct attacking M. aeruginosa rather than excretion of algicides. Furthermore, strain KT48 led to an increase in cellular reactive oxygen species (ROS) and caused lipid peroxidation as supported by the increase in malondialdehyde (MDA) levels. The ROS and MDA levels in algal cells treated with strain KT48 cells re-suspended were about 3.23-fold and 2.80-fold higher than those of untreated algal cells on day 11. And a further inhibition to the antioxidant system is suggested by a sharp decrease in the superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities. In addition, we also observed that the morphology of most algal cells changed from integrity to break. This study not only indicated strain KT48 with strong algicidal activity, but also explored the underlying algicidal mechanisms to provide a source of bacterial agent for the biocontrol of cyanobacterial blooms. KEY POINTS: • Strain KT48 exhibited strong algicidal activity mainly through direct attacking M. aeruginosa. • The addition of glucose could enhance the algicidal rate of strain KT48 by about 30%. • Strain KT48 led to an increase in cellular reactive oxygen species (ROS) level that causes membrane damage as supported by the increase in malondialdehyde (MDA) levels.

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.

Disentangling the drivers of phytoplankton community composition in a heavily sediment-laden transcontinental river

Phytoplankton play a crucial role in energy flow and carbon cycling in aquatic ecosystems; however, exploring the driving factors influencing phytoplankton, especially in heavily sediment-laden rivers, is challenging. We analyzed 704 samples from 44 sampling sites along the Yellow River to investigate the biogeographic, environmental, and anthropogenic impacts on the phytoplankton community composition. Using cluster analysis, we identified three different phytoplankton community compositions in Regions Ⅰ, Ⅱ, and Ⅲ, which were consistent with the three primary changes in the water-surface slope across the three regions. The sampling results showed that the Bacillariophyta primarily consisted of Navicula, Cyclotella, Synedra, Fragilaria, Gyrosigma, Diatoma, and Asterionella. In addition, representation by Chlorophyta was dominated by Chlamydomonas, Pandorina, Closteriopsis, and Closterium, while Phormidium was the dominant Cyanophyta genus. The variation partitioning results indicated that spatial factors (geographic distance) were the most important determinants of phytoplankton community succession. Additionally, our results highlighted that the influence of spatial and climatic factors on the succession of the phytoplankton community structure was much greater than that of the water quality. Compared to that in the free-flowing river, the phytoplankton biomass in the impoundment was much higher, and the phytoplankton community was dominated by Dinophyta, Chlorophyta, and Cyanophyta, primarily because of anthropogenic impacts. Based on the composition and biomass of phytoplankton communities in different regions, the phytoplankton community composition in the Yellow River was found to be primarily influenced by the erosion of the watershed and the inflow of tributaries rather than by limited in situ algae growth.

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.

Insights into diatom microalgal farming for treatment of wastewater and pretreatment of algal cells by ultrasonication for value creation

Wastewater management and its treatment have revolutionized the industry sector into many innovative techniques. However, the cost of recycling via chemical treatment has major issues especially in economically poor sectors. On the offset, one of the most viable and economical techniques to clean wastewater is by growing microalgae in it. Since wastewater is rich in nitrates, phosphates and other trace elements, the environment is suitable for the growth of microalgae. On the other side, the cost of harvesting microalgae for its secondary metabolites is burgeoning. While simultaneously growing of microalgae in photobioreactors requires regular feeding of the nutrients and maintenance which increases the cost of operation and hence cost of its end products. The growth of microalgae in waste waters makes the process not only economical but they also manufacture more amounts of value added products. However, harvesting of these values added products is still a cumbersome task. On the offset, it has been observed that pretreating the microalgal biomass with ultrasonication allows easy oozing of the secondary metabolites like oil, proteins, carbohydrates and methane at much lower cost than that required for their extraction. Among microalgae diatoms are more robust and have immense crude oil and are rich in various value added products. However, due to their thick silica walls they do not ooze the metabolites until the mechanical force on their walls reaches certain threshold energy. In this review recycling of wastewater using microalgae and its pretreatment via ultrasonication with special reference to diatoms is critically discussed. Perspectives on circular bioeconomy and knowledge gaps for employing microalgae to recycle wastewater have been comprehensively narrated.

Characterization of Intracellular Structure Changes of Microcystis under Sonication Treatment by Polarized Light Scattering

Cyanobacterial bloom is one of the most urgent global environmental issues, which eventually could threaten human health and safety. Sonication treatment (ST) is a potential effective method to control cyanobacteria blooms in the field. Currently, the bottleneck of extensive application of ST is the difficulty to estimate the ST effect on the cyanobacterial cells and then determine suitable ST times in the field. In this study, cyanobacterial Microcystis samples sonicated at different times were first measured by a spectrophotometer to calculate the removal efficiency of Microcystis cells. Additionally, they were observed by TEM to reveal the intracellular structure changes of the cells. Then the samples were measured by an experimental setup based on polarized light scattering to measure the polarization parameters. Experimental results indicated that the polarization parameters can effectively characterize the intracellular structural changes of Microcystis cells with different ST times, which is quite consistent with the results for removal efficiency and TEM images. Further, the optimal ST time can be inferred by the polarization parameters. These results demonstrate that polarized light scattering can be a potentially powerful tool to explore suitable times for sonication treatment of cyanobacteria blooms.

A Streptomyces globisporus strain kills Microcystis aeruginosa via cell-to-cell contact

Cyanobacterial harmful algal blooms (CyanoHABs) bring economic loss, damage aquatic ecosystems, and produce cyanobacterial toxins that threaten human health. Algicidal bacteria as pathogens can expediate the decline of CyanoHABs. In this study, a Streptomyces globisporus strain (designated G9), isolated from soil near a eutrophic pond, showed high algicidal activity against Microcystis aeruginosa. Experimental results show that G9 preyed on Microcystis through cell-to-cell contact: (1) the hyphae of G9 killed cyanobacterial cells by twining around them, while cells beyond the reach of G9 hyphae were in normal shapes; (2) No algicides were detectable in the supernatant of G9 cultures or G9-Microcystis cocultures. The algicidal ratio of G9 to M. aeruginosa reached 96.7% after 6 days. G9 selectively killed the tested cyanobacterial strains, while it had only minor impacts on the growth of tested Chlorophyceae. Differential gene expression studies show that G9 affected the expression of key genes of M. aeruginosa involved in photosynthesis, microcystin synthesis and cellular emergency responses. Further, the microcystin-LR content decreased gradually with G9 treatment. As the first reported Streptomyces sp. with algicidal (predation) activity requiring cell-to-cell contact with target prey, G9 is a good candidate for the exploration of additional cyanobacteria-bacteria interactions and the development of novel strategies to control CyanoHABs.

Comparison of Different Anode Materials to Remove Microcystis aeruginosa Cells Using Electro-Coagulation–Flotation Process at Low Current Inputs

Cyanobacterial blooms are a threat to the drinking water supply owing to their potential toxicity. Microcystins which are the most widespread cyanotoxins, are mainly produced by Microcystis spp. In this study, we cultured Microcystis aeruginosa cells in BG-11 medium at 25 °C to investigate the efficiency of the electro-coagulation–flotation process to remove them. Different anode materials (Fe, Al, Cu, and Zn) along with a graphite cathode were compared separately in the 10–100 mA current range in a 0.025 M Na2SO4 electrolyte. Turbidity, optical density at 684 nm (OD684), OD730, Chl-a concentration, and DOC concentration were analyzed to clarify the mechanism by which M. aeruginosa cells are removed. The Al anode indicated the highest removal efficiencies in terms of turbidity (90%), OD684 and OD730 (98%), and Chl-a concentration (96%) within 30 min at 4.0 mA/cm2 current density and the lowest average electrode consumption of 0.120 ± 0.023 g/L. The energy consumption of the Al electrode was 0.80 Wh/L. From these results, we found that Al was the best among the anode materials evaluated to remove M. aeruginosa cells. However, further studies are required to optimize the Al anode in terms of pH, treatment time, electrode distance, and electrolyte concentration to enhance the removal of M. aeruginosa cells.

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

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.

Inactivation of harmful Anabaena flos-aquae by ultrasound irradiation: Cell disruption mechanism and enhanced coagulation

Harmful algal blooms pose a potential threat to the safety of drinking water sources. Ultrasound is an effective method for algae removal. However, this method can lead to the release of algal organic matter and the effects and toxic mechanisms of ultrasound on Anabaena are still poorly understood. The destruction mechanism of Anabaena flos-aquae cells under different ultrasonic conditions, the safety of intracellular organic matter (IOM) release to water and the enhanced coagulation efficiency of ultrasound were studied. Results showed that high-frequency ultrasound was effective in breaking down algae cells. After 10 min ultrasonication at 20 kHz, 5 min at 740 kHz and 1 min at 1120 kHz, the algae cells were inactivated and algae growth was halted. Ultrasound radiation can lead to the release of IOM, primarily chlorophyll a and phycocyanin, followed by some tryptophan and humic substances, polysaccharides, and proteins. The sonicated ribosomes were considerably reduced, and the antioxidant system of cells was also damaged to some extent. The coagulation effect of algae cells was substantially improved after ultrasonication. Thus, the safety of algae cell removal could be improved by controlling the changes in physiological structure and IOM release of algae cells by adjusting the ultrasound parameters.

Response of Scenedesmus sp. to microwave treatment: Enhancement of lipid, exopolysaccharide and biomass production

The present study focuses on the use of microwave irradiation to improve the production of lipid, exopolysaccharide and biomass in the microalgae Scenedesmus sp. Microwave treatment conditions such as microwave power, duty cycle % and time was optimized to increase the biomass and lipid content of Scenedesmus sp. Microwave power 100 W, duty cycle 40 %, and 2 min treatment time led to a substantial improvement in the biomass and lipid content. Due to the simultaneous improvement in both the biomass and lipid content, the total lipid production was improved from 0.76 (microwave untreated) to 1.42 g/L (microwave treated) (12 days grown cells). In addition, with biomass and lipid content, microwave treatment also enhanced the production of Exopolysaccharides (EPS) up to 2.3-folds. Furthermore, biodiesel properties were improved to some extent after the microwave treatment. Microwave irradiation is a promising physical treatment method for microalgae to improve total lipid production.

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.

Application progress of enhanced coagulation in water treatment

Water industries worldwide consider coagulation/flocculation to be one of the major treatment methods for improving the overall efficiency and cost effectiveness of water and wastewater treatment. Enhancing the coagulation process is currently a popular research topic. In this review article, the latest developments in enhanced coagulation are summarized. In addition, the mechanisms of enhanced coagulation and the effect of process parameters on processing efficiency are discussed from the perspective of ballast-enhanced coagulation, preoxidation, ultrasound, and composite coagulants. Finally, improvements and new directions for enhanced coagulation are proposed.

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.

Amentoflavone, a novel cyanobacterial killing agent from Selaginella tamariscina

Harmful cyanobacterial bloom (HCB) by Microcystis aeruginosa is increasingly becoming a serious concern to the environment and human health alike. Currently, many physical, chemical, and biological controls are underway to eliminate HCB, but natural chemicals are rarely used. To find a control agent with low environmental toxicity and high potential for practical use, 60 plant extracts were screened. Only Selaginella tamariscina extract killed all four Microcystis aeruginosa strains, but not the other tested bacteria. Chloroform fraction of S. tamariscina extract (CSE) showed the highest killing activity. The effects of CSE on M. aeruginosa were monitored using differential interference contrast microscopy and flow-cytometry analysis, scanning electron microscopy, and transmission electron microscopy. The images showed that CSE-treated cells were abnormally altered, with damaged cell membranes, peptidoglycan layers, and cytoplasm. Quadrupole time-of-flight liquid chromatography-mass spectrometry was used to identify amentoflavone as a major active compound. Pure amentoflavone, even at low concentrations showed a powerful killing effect on M. aeruginosa, but not on other non-cyanobacteria. Overall, in this study, we have highlighted the potentials of S. tamariscina extracts and amentoflavone as selective HCB control agents.

Effects of cavitation on different microorganisms: The current understanding of the mechanisms taking place behind the phenomenon. A review and proposals for further research

A sudden decrease in pressure triggers the formation of vapour and gas bubbles inside a liquid medium (also called cavitation). This leads to many (key) engineering problems: material loss, noise, and vibration of hydraulic machinery. On the other hand, cavitation is a potentially useful phenomenon: the extreme conditions are increasingly used for a wide variety of applications such as surface cleaning, enhanced chemistry, and wastewater treatment (bacteria eradication and virus inactivation). Despite this significant progress, a large gap persists between the understanding of the mechanisms that contribute to the effects of cavitation and its application. Although engineers are already commercializing devices that employ cavitation, we are still not able to answer the fundamental question: What precisely are the mechanisms how bubbles can clean, disinfect, kill bacteria and enhance chemical activity? The present paper is a thorough review of the recent (from 2005 onward) work done in the fields of cavitation-assisted microorganism's destruction and aims to serve as a foundation to build on in the next years.

Silica-quaternary ammonium "Fixed-Quat" nanofilm coated fiberglass mesh for water disinfection and harmful algal blooms control

Intensification of pollution loading worldwide has promoted an escalation of different types of disease-causing microorganisms, such as harmful algal blooms (HABs), instigating detrimental impacts on the quality of receiving surface waters. Formation of unwanted disinfection by-products (DBPs) resulting from conventional disinfection technologies reveals the need for the development of new sustainable alternatives. Quaternary Ammonium Compounds (QACs) are cationic surfactants widely known for their effective biocidal properties at the ppm level. In this study, a novel silica-based antimicrobial nanofilm was developed using a composite of silica-modified QAC (Fixed-Quat) and applied to a fiberglass mesh as an active surface via sol-gel technique. The synthesized Fixed-Quat nanocoating was found to be effective against E. coli with an inactivation rate of 1.3 × 10^-3 log reduction/cm min. The Fixed-Quat coated fiberglass mesh also demonstrated successful control of Microcystis aeruginosa with more than 99% inactivation after 10 hr of exposure. The developed antimicrobial mesh was also evaluated with wild-type microalgal species collected in a water body experiencing HABs, obtaining a 97% removal efficiency. Overall, the silica-functionalized Fixed-Quat nanocoating showed promising antimicrobial properties for water disinfection and HABs control, while decreasing concerns related to DBPs formation and the possible release of toxic nanomaterials into the 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.

An algicidal Streptomyces amritsarensis strain against Microcystis aeruginosa strongly inhibits microcystin synthesis simultaneously

Microcystis aeruginosa and hepatotoxic microcystins produced by it have posed a severe threat to aquatic ecological security and human health. In this study a Streptomyces amritsarensis HG-16, showing high algicidal activity against M. aeruginosa and strong inhibitory effect on microcystin synthesis, was obtained by screening some anti-Fusarium sp. microbial strains isolated before in our laboratory. HG-16 bound cyanobacterial cells by mycelia to form flocs and killed M. aeruginosa by secreting active substances, which were proteinase K resistant and stable in the temperature range of 35-75 °C and pH range of 3-11. HG-16 removed M. aeruginosa of 10⁵ and 10⁶ cell mL^-1 cell densities in similar rate and was active against all the tested harmful unicellular and filamentous cyanobacteria. Results of differential gene expression analysis indicated that HG-16 affected the photosynthesis system and microcystin synthesis of M. aeruginosa. Accordingly, the algicidal activity of HG-16 was light-dependent, and microcystin synthesis of M. aeruginosa decreased by 91.2% with HG-16 treatment. Thus, it is promising to utilize HG-16 to mitigate harmful cyanobacterial blooms, inhibit microcystin synthesis and control plant disease caused by Fusarium.spp. through irrigating farmland with eutrophic water applied HG-16.

An environmentally friendly approach for mitigating cyanobacterial bloom and their toxins in hypereutrophic ponds: Potentiality of a newly developed granular hydrogen peroxide-based compound

Cyanobacterial blooms and their associated toxins are growing issues for many aquatic resources, and pose a major threat to human health and ecological welfare. To control cyanobacterial blooms and their toxins, the efficacy of a newly developed granular compound (sodium carbonate peroxyhydrate 'SCP', trade name 'PAK® 27' algaecide) containing hydrogen peroxide (H₂O₂) as the active ingredient was investigated. First, the dose efficacy of the SCP that corresponded to 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 5.0 and 8.0 mg/L H₂O₂ was tested for 10 days in small-scale tanks installed in 0.1-acre experimental hypereutrophic ponds dominated by blooms of the toxic cyanobacterium Planktothrix sp. SCP ranging from 2.5-4.0 mg/L H₂O₂ selectively killed Planktothrix sp. without major impacts on either eukaryotic phytoplankton (e.g., diatom Synedra sp., green algae Spirogyra sp. and Cladophora sp.) or zooplankton (e.g., rotifers Brachionus sp. and cladocerans Daphnia sp.). Based on these results, SCP at 2.5 mg/L and 4.0 mg/L H₂O₂ were homogeneously introduced into entire water volume of the experimental ponds in parallel with untreated control ponds. The dynamics of cyanobacterium Planktothrix sp., microcystins (commonly occurring cyanotoxins), eukaryotic phytoplankton, zooplankton, and water quality parameters were measured daily for 10 days and followed by a weekly sampling for 6 weeks. Temporal analysis indicated that Planktothrix sp. blooms collapsed remarkably in both 2.5 mg/L and 4.0 mg/L H₂O₂ treatments. Both treatments also were accompanied by an overall reduction in the total microcystin concentration. At 2.5 mg/L H₂O₂, the growth of eukaryotic phytoplankton (Synedra and Cladophora sp.) increased, but these populations along with zooplankton (Brachionus and Daphnia sp.) were suppressed at 4.0 mg/L H₂O₂. The longevity of 2.5 and 4.0 mg/L H₂O₂ treatment effects were up to 5 weeks. In addition, the added granular algaecide degraded within a few days, thereby leaving no long-term traces of H₂O₂ in the environment.

Formation of inorganic nitrogenous byproducts in aqueous solution under ultrasound irradiation

The effects of ultrasonic frequency, power intensity, temperature and sparged gas on the generation of nitrogenous by-products NO₂^- and NO₃^- have been investigated, and the new kinetics model of NO₂^- and NO₃^- generation was also explored. The results show that the highest primary generation rate of NO₂^- and NO₃^- by direct sonolysis in the cavitation bubbles (represented by k₁' and k₂', respectively) was obtained at 600 kHz and 200 kHz, respectively, in the applied ultrasonic frequency range of 200 to 800 kHz. The primary generation rate of NO₂^- (represented by k₁') increased with the increasing ultrasonic intensity while the primary generation rate of NO₃^- (represented by k₂') decreased. The lower temperature is beneficial to the primary generation of both NO₂^- and NO₃^- in the cavitation bubbles. The optimal overall yields of both NO₂^- and NO₃^- were obtained at the N₂/O₂ volume (in the sparged gas) ratio of 3:1 which is near to the ratio of N₂/O₂ in air. The dissolved O₂ is the dominant oxygen element source for both NO and NO₂, compared with water vapor. Ultrasonic irradiation can significant enhance the recovery rates of dissolved N₂ and O₂ and thus keep the N₂ fixation reaction going even without aeration.

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.

Buoyancy Limitation of Filamentous Cyanobacteria under Prolonged Pressure due to the Gas Vesicles Collapse

Freshwater cyanobacterium Pseudanabaena galeata were cultured in chambers under artificially generated pressures, which correspond to the hydrostatic pressures at deep water. Variations occurred in gas vesicles volume, and buoyancy state of cells under those conditions were analyzed at different time intervals (5 min, 1 day, and 5 days). Variations in gas vesicles morphology of cells were observed by transmission electron microscopy images. Settling velocity (Vs) of cells which governs the buoyancy was observed with the aid of a modified optical microscope. Moreover, effects of the prolonged pressure on cell ballast composition (protein and polysaccharides) were examined. Elevated pressure conditions reduced the cell ballast and caused a complete disappearance of gas vesicles in Pseudanabaena galeata cells. Hence cyanobacteria cells were not able to float within the study period. Observations and findings of the study indicate the potential application of hydrostatic pressure, which naturally occurred in hypolimnion of lakes, to inhibit the re-suspension of cyanobacteria cells.

A Bacillus sp. strain with antagonistic activity against Fusarium graminearum kills Microcystis aeruginosa selectively

Cyanobacterial harmful algal blooms (CyanoHABs) cause severe environmental problems, economic losses and threaten human health seriously. In the present study, a Bacillus sp. strain, designated as AF-1, with strong antagonistic activity against plant pathogenic fungus Fusarium graminearum was isolated from purple soil. Bacillus sp. AF-1 selectively killed Microcystis aeruginosa at low cell density (1.6×10³cfu/mL), and showed the strongest bactericidal activity against M. aeruginosa NIES-843 (A_e=93%, t=6d). The algicidal substances originated from strain AF-1 were stable in the temperature range of 35-100°C, and pH range of 3-11. Cell-free filtrate of AF-1 culture caused excessive accumulation of intracellular reactive oxygen species (ROS), cell death and the efflux of intracellular components of M. aeruginosa NIES-843 cells. The expression of genes recA, psbA1, psbD1, rbcL and mcyB, involved in DNA repair, photosynthesis and microcystin synthesis of NIES 843, were significantly influenced by the cell-free filtrate of AF-1 culture. Bacillus sp. AF-1 has the potential to be developed as a bifunctional biocontrol agent to control CyanoHABs and F. graminearum caused plant disease.

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.

Physiological responses of Microcystis aeruginosa against the algicidal bacterium Pseudomonas aeruginosa

Proliferation of cyanobacteria in aquatic ecosystems has caused water security problems throughout the world. Our preliminary study has showed that Pseudomonas aeruginosa can inhibit the growth of cyanobacterium, Microcystis aeruginosa. In order to explore the inhibitory mechanism of P. aeruginosa on the cell growth and synthesis of intracellular substances of M. aeruginosa, concentrations of Chlorophyll-a, intracellular protein, carbohydrate, enzyme activities and ion metabolism of M. aeruginosa, were investigated. The results indicated that 83.84% algicidal efficiency of P. aeruginosa was achieved after treatment for 7 days. The strain inhibited the reproduction of M. aeruginosa by impeding the synthesis of intracellular protein and carbohydrate of cyanobacterium, and only a very small part of intracellular protein and carbohydrate was detected after exposure to P. aeruginosa for 5 days. P. aeruginosa caused the alteration of intracellular antioxidant enzyme activity of M. aeruginosa, such as catalase, peroxidase. The accumulation of malondialdehyde aggravated membrane injury after treatment for 3 days. P. aeruginosa also affected the ion metabolism of cyanobacteria. The release of Na(+) and Cl(-) was significantly enhanced while the uptake of K(+), Ca(2+), Mg(2+), NO3(-) and SO4(2)(-) decreased. Surface morphology and intracellular structure of cyanobacteria and bacterial cells changed dramatically over time as evidenced by electron microscope (SEM) and transmission electron microscope (TEM) analysis. These results revealed that the algicidal activity of P. aeruginosa was primarily due to the fermentation liquid of P. aeruginosa that impeded the synthesis of intracellular protein and carbohydrate, and damaged the cell membrane through membrane lipid peroxidation.

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.