In situ algal bloom control by the integration of ultrasonic radiation and jet circulation to flushing

Interactions between tannins allelochemicals and extracellular polymeric substance (EPS) of Microcystis aeruginosa

The protective mechanism of extracellular polymeric substance (EPS) secreted by a harmful cyanobacteria against tannins allelochemicals was explored in this study. The binding properties of soluble EPS (SEPS) and bound EPS (BEPS) of Microcystis aeruginosa to tannic acid (TA) were investigated via fluorescence spectroscopy. The results suggested that TA interacted with the proteins in SEPS and BEPS mainly with binding constants of 5.26 and 7.93 L/mol, respectively; TA interacted with the humic acids in SEPS and BEPS mainly with binding constants of 5.12 and 5.24 L/mol, respectively. Thermodynamic experiments confirmed that the binding was mainly controlled by the hydrophobic force. Combined with Fourier transform infrared spectroscopy, it was found that the amine, carbonyl, carboxyl, and hydroxyl groups in EPS were the main functional groups contributing to the interaction of TA with EPS. The existence of EPS reduced the toxicity of TA to algal cells, with the 96 h inhibition rate of 40 mg L^-1 TA on algal cells decreasing by 48.95%. The results of this study may improve our understanding of the protective mechanism of cyanobacteria against tannins allelochemicals.

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.

Simultaneous removal of colonial Microcystis and microcystins by protozoa grazing coupled with ultrasound treatment

Removal of harmful cyanobacteria is an extremely urgent task in global lake management and protection. Conventional measures are insufficient for simultaneously removing cyanobacteria and hazardous cyanotoxin, efficient and environmental-friendly measures are therefore particularly needed. Herbivorous protozoa have great potentials in controlling algae, however, large-sized colonial Microcystis is inedible for protozoa, which is a central problem to be solved. Therefore, in present study, a measure of protozoa grazing assisted by ultrasound was investigated in laboratory scale for eliminating harmful colonial Microcystis. The results showed that with ultrasound power and time increasing, the proportion of unicellular Microcystis increased significantly. With Ochromonas addition, approximately 80% of colonial Microcystis and microcystin was removed on day 4 under ultrasound power of 100 W for 15 min, while Ochromonas only reduced Microcystis by less than 20% without assistance of ultrasound. Moreover, when directly exposed to low-intensity ultrasound, Ochromonas showed strong resistance to ultrasound and were not inhibited in grazing Microcystis. Overall, ultrasound increases edible food for protozoa via collapsing Microcystis colonies and assists Ochromonas to remove Microcystis, thus intermittently collapsing colonial Microcystis using low-intensity ultrasound can significantly improve the removal efficiency of Microcystis by protozoa grazing, which provided a new insight in controlling harmful colonial Microcystis.

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.

Questiomycins, Algicidal Compounds Produced by the Marine Bacterium Alteromonas sp. D and Their Production Cue

Questiomycin A (1) along with three new compounds, questiomycins C–E (2–4), were isolated from culture of Alteromonas sp. D, an algicidal marine bacterium, guided by algal lethality assay using the raphidophyte, Chattonella antiqua, one of the causative organisms of harmful algal bloom. The structures of 1–4 were assigned on the basis of their spectrometric and spectroscopic data. Compounds 1 to 4 exhibited algicidal activity against C. antiqua with LC₅₀ values ranging from 0.18 to 6.37 μM. Co-cultivation experiment revealed that 1 was produced only when the microalgae and the bacterium are in close contact, suggesting that some interactions between them trigger the biosynthesis of questiomycins. These results suggested that the algicidal bacteria such as Alteromonas sp. D can control microalgae chemically in marine ecosystem.

Removal of Microcystis aeruginosa by ultrasound: Inactivation mechanism and release of algal organic matter

The efficacy of ultrasonic irradiation for removal of Microcystis aeruginosa and release of algal organic matter (AOM) was investigated under different ultrasound conditions, including ultrasonic frequency, power density, and time. Laboratory results suggested that the ultrasonic efficiency and the release of AOM were influenced by frequency, power density, and time. The mechanism of AOM algae removal by ultrasound was systematically explored. The inactivation of algae resulted from mechanical and chemical effects caused by ultrasound. Mechanical destruction and free-radical oxidation considerably affected the structure and physiological function of algal cells. The SEM and TEM images indicated that ultrasound could damage the cell membrane, wall, and organelle. Flow cell cytometry results showed decreases in the size, internal granularity, integrity, and activity of algal cells, revealing that ultrasound exerted severe damage to the structure and function of algal cells. The activity of the antioxidant system of algal cells was then studied by investigating changes in MDA, SOD, and CAT concentration after ultrasound to confirm the inactivation of the cells. The release of AOM was explored by determining changes in water quality indices (UV254, DOC, and SUVA) at 10 min and 48 h after ultrasound. This study provides information about the safety of ultrasound usage on algae removal and references for ultrasonic parameters to be selected to ensure effective and safe algae removal.

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.

Microorganisms-based methods for harmful algal blooms control: A review

Harmful algal blooms (HABs) are a worldwide problem with numerous negative effects on water systems, which have prompted researchers to study applicable measures to inhibit and control them. This review summarized the current microorganisms-based methods or technologies aimed at controlling HABs. Based on their characteristics, these methods can be divided into two categories: methods based on single-species microorganisms and methods based on microbial aggregates, and four types: methods for rapid decrease of algal cells density (e.g., alga-bacterium and alga-fungus bioflocculation), inhibition of harmful algal growth, lysis of harmful algae (e.g. algicidal bacteria, fungi, and actinomycete), and methods based on microbial aggregates (periphytons and biofilms). An integrative process of "flocculation-lysis-degradation-nutrients regulation" is proposed to control HABs. This review not only offers a systematic understanding of HABs control technologies based on microorganisms but also elicits a re-thinking of HABs control based on microbial aggregates.

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.

The effect of hydrodynamic cavitation on Microcystis aeruginosa: Physical and chemical factors

The various effects of hydrodynamic cavitation (HC) on algal growth inhibition were investigated. The gas-vacuolate species Microcystis aeruginosa responded differently to the gas-vacuole-negative alga Chlorella sp. When M. aeruginosa was subjected to HC, both its cell density and photosynthetic activity were subsequently reduced by nearly 90% after three days culture. However, the cell density of Chlorella sp. was reduced by only 63%, and its final photosynthetic activity was unaffected. Electron microscopy confirmed that HC had a minimal impact on algal cells that lack gas vacuoles. Shear stress during recirculation only modestly inhibited the growth of M. aeruginosa. The relative malondialdehyde (MDA) content, a quantitative indicator of lipid peroxidation, increased significantly during HC treatment, indicating the production of free radicals. Accordingly, the addition of H2O2 to the HC process promoted the production of free radicals, which also improved algal reduction. A comparison of the outcomes and energy efficiency of HC and ultrasonic cavitation indicated that HC gives the best performance: under 10 min cavitation treatment, the algal removal rate of HC could reach 88% while that of sonication was only 39%.

Removal of Microcystis aeruginosa using hydrodynamic cavitation: performance and mechanisms

Algal blooms are a seasonal problem in eutrophic water bodies, and novel approaches to algal removal are required. The effect of hydrodynamic cavitation (HC) on the removal of Microcystis aeruginosa was investigated using a laboratory scale device. Samples treated by HC were subsequently grown under illuminated culture conditions. The results demonstrated that a short treatment with HC could effectively settle naturally growing M. aeruginosa without breaking cells. Algal cell density and chlorophyll-a of a sample treated for 10 min were significantly decreased by 88% andv 94%, respectively, after 3 days culture. Various HC operating parameters were investigated, showing that inhibition of M. aeruginosa growth mainly depended on treatment time and pump pressure. Electron microscopy confirmed that sedimentation of algae was attributable to the disruption of intracellular gas vesicles. Damage to the photosynthetic apparatus also contributed to the inhibition of algal growth. Free radicals produced by the cavitation process could be as an indirect indicator of the intensity of HC treatment, although they inflicted minimal damage on the algae. In conclusion, we suggest that HC represents a potentially highly effective and sustainable approach to the removal of algae from water systems.

Combination of uniform design with artificial neural network coupling genetic algorithm: an effective way to obtain high yield of biomass and algicidal compound of a novel HABs control actinomycete

Controlling harmful algae blooms (HABs) using microbial algicides is cheap, efficient and environmental-friendly. However, obtaining high yield of algicidal microbes to meet the need of field test is still a big challenge since qualitative and quantitative analysis of algicidal compounds is difficult. In this study, we developed a protocol to increase the yield of both biomass and algicidal compound present in a novel algicidal actinomycete Streptomyces alboflavus RPS, which kills Phaeocystis globosa. To overcome the problem in algicidal compound quantification, we chose algicidal ratio as the index and used artificial neural network to fit the data, which was appropriate for this nonlinear situation. In this protocol, we firstly determined five main influencing factors through single factor experiments and generated the multifactorial experimental groups with a U₁₅(15⁵) uniform-design-table. Then, we used the traditional quadratic polynomial stepwise regression model and an accurate, fully optimized BP-neural network to simulate the fermentation. Optimized with genetic algorithm and verified using experiments, we successfully increased the algicidal ratio of the fermentation broth by 16.90% and the dry mycelial weight by 69.27%. These results suggested that this newly developed approach is a viable and easy way to optimize the fermentation conditions for algicidal microorganisms.

Evaluation of thermal, ultrasonic and alkali pretreatments on mixed-microalgal biomass to enhance anaerobic methane production

Anaerobic digestion was regarded as one of the ways to recover energy from mixed-microalgae biomass in this study. After applying thermal-, ultrasonic-, and alkali-pretreatments to raw microalgae biomass to promote the digestion efficiency, a biochemical methane potential was investigated to evaluate the effectiveness of the pre-treatments for the purpose. As the pretreatment intensity increased, the solubilization of the mixed microalgae increased. However, the increased solubilization was not followed proportionally by the increased methane production. The highest methane productivity was achieved by the thermal-pretreatment at 120 °C (405 mL CH4/g-VS), which was 1.2 times higher than that of the non-pretreatment condition (336 mL CH4/g-VS). The net energy analysis revealed that only the pretreatment adjusted to pH 9 yielded a slightly higher energy gains (12.8 kJ/g-VS) than that of non-pretreatment condition (11.9 kJ/g-VS). These findings recommend direct supply of microalgae biomass for anaerobic digestion.

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 efficiency of a constructed wetland combined with ultrasound and UV devices for wastewater reuse in agriculture

This study evaluates the treatment efficiency of a chemical-free water treatment for treating the secondary effluent of a municipal wastewater treatment plant with the aim of reusing the water for agriculture. Urban wastewater was treated by three units run in series: a full-scale horizontal sub-surface flow constructed wetland, a small pond with an ultrasound (US) system and a UV device. The treatment efficiency was evaluated in terms of the Italian wastewater limits for irrigation reuse, water quality improvement (removal percentage) and algae bloom control. The tolerable infection risk, associated with the use of wastewaters for irrigating crops, was also assessed by applying the microbial risk analyses proposed in the WHO guidelines for wastewater reuse. The constructed wetland was efficient in reducing physical-chemical and microbiological concentrations, and its efficiency was very steady over the investigation period. The UV system significantly improved water quality (p<0.05) in terms of pathogen concentration with a further average decrease from 0.35 to 1.23 log units, depending on the microbiological parameter. The US device was able to prevent algae bloom on a free water surface and maintain Chlorophyll-a concentration stable and low 2 months after activation.

Cyanotoxins: characteristics, production and degradation routes in drinking water treatment with reference to the situation in Serbia

Cyanobacteria are members of phytoplankton of the surface freshwaters. The accelerated eutrophication of freshwaters, especially reservoirs for drinking water, by human activity has increased the occurrence and intensity of cyanobacterial blooms. They are of concern due to their ability to produce taste and odors compounds, a wide range of toxins, which have a hepatotoxic, neurotoxic, cytotoxic and dermatotoxic behavior, being dangerous to animal and human health. Therefore, the removal of cyanobacteria, without cell lysis, and releasing of intracellular metabolites, would significantly reduce the concentration of these metabolites in the finished drinking water, as a specific aim of the water treatment processes. This review summarizes the existing data on characteristics of the cyanotoxins, their productions in environment and effective treatment processes to remove these toxins from drinking water.

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.

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.

Effects of an algicidal bacterium Pseudomonas mendocina on the growth and antioxidant system of Aphanizomenon flos-aquae

Evident effect of an algicidal bacterium Pseudomonas mendocina on the growth and antioxidant system of Aphanizomenon flos-aquae was detected in this experiment. Seven parameters including the chlorophyll a contents, Fv/Fm values, reactive oxygen species (ROS), malonaldehyde (MDA), catalase (CAT), peroxide dismutase (POD), and superoxide dismutase (SOD) were tested in the cyanobacterium A. flos-aquae cells after inoculation with the algicidal bacterium Pseudomonas mendocina DC10. It was shown from the experiment that the growth of the treated cyanobacterium A. flos-aquae was significantly restrained, which was expressed as great reductions in the chlorophyll a contents and Fv/Fm values. At the same time, the treated cyanobacterial cells exhibited an obvious increase in the production of ROS and MDA compared with the control. CAT and POD activities in the treated group kept at high level, however, they both reduced significantly on day 6. SOD activities in the treated A. flos-aquae showed obvious declines after inoculation, and great augmentations on day 3 and 4, thereafter, they kept in a declining tendency. The results showed the oxidative stresses induced by the bacterium could be a killing agent of the cyanobacterium A. flos-aquae cells.

Ultrasound-enhanced coagulation for Microcystis aeruginosa removal

Source water eutrophication has caused serious problems in drinking water supplies, with enhanced coagulation widely used to remove the resulting algae. This paper investigates the use of sonication to improve the removal by coagulation of Microcystis aeruginosa, a common species of toxic algae. The results show that sonication significantly enhances the reduction of algae cells, solution UV254, and chlorophyll a without increasing the concentration of aqueous microcystins. The main mechanism involved the destruction during ultrasonic irradiation of gas vacuoles inside algae cells that acted as 'nuclei' for acoustic cavitation and collapse during the "bubble crush" period, resulting in the settlement of cyanobacteria. Coagulation efficiency depended strongly on the coagulant dose and sonication conditions. When the coagulant dose was 0.5mg/l, 5s of ultrasonic irradiation increased algae removal efficiency from 35% to 67%. As further sonication enhanced the coagulation efficiency only slightly due to better mixing, optimal sonication time was 5s. The most effective sonication intensity was 47.2W/cm2, and the highest removal ratio of M. aeruginosa was 93.5% by the sonication-coagulation method. Experiments with reservoir water showed that this method could be successfully applied to natural water containing multiple species of algae.

Ultrasonic damages on cyanobacterial photosynthesis

Excessive cyanobacterial growth in eutrophic water sources has been a serious environmental problem, and both sight preservation and drinking water production demand control of cyanobacterial growth in water. Ultrasonic treatment was reported to effectively inhibit cyanobacterial growth through vesicle collapsing and cell fracturing, but little was known about the change of cyanobacterial photosynthesis during sonication. This paper examined the ultrasonic inhibition of Microcystis aeruginosa cell growth and extracellular microcystins release, and the instant ultrasonic decreases of antenna complexes like cyanobacterial chlorophyll a and phycocyanins (PC), and the oxygen evolution rate. The results showed that sonication effectively damaged antenna complexes, slowed down the photo-activity, which significantly inhibited the cell growth and microcystins formation and release.

Ultrasonic frequency effects on the removal of Microcystis aeruginosa

Algae bloom in source water causes high chemical consumption and deteriorates water quality in waterworks. This paper studied the ultrasonic removal of Microcystis aeruginosa. The results showed that algae cells could be effectively removed by sonication and gas vesicle collapse was the main mechanism. The ultrasonic algae removal followed the first order reaction with a rate constant of 0.023 min(-1) (80 W, 80 kHz). Higher ultrasound frequency benefited algae removal; the algae removal rate constant was 0.114 min(-1) at 1320 kHz and 0.0224 min(-1) at 20 kHz (80 W). Higher ultrasound power also accelerated algae removal; the algae removal rate constant was 0.023 min(-1) at 80 W and 0.007 min(-1) at 32 W (80 kHz). However, high ultrasound power and long irradiation caused microcystins to increase. 80 W, 80 kHz sonication for 5 min increased the extracellular microcystins concentration from 0.87 microg/L to 3.11 microg/L. Sound frequency had little impact on the microcystins release. The chlorophyll a concentration initially decreased and then stabilized after 5 min of sonication.

Removal of algae by sonication-coagulation

Algae bloom in source water has caused serious problems in drinking water supplies, and conventional methods for its treatment have achieved only limited success. This paper reports a new technology, ultrasound assisted coagulation, for effective removal of algae cells from the source water in water treatment works. The results showed that ultrasonic pretreatment significantly enhanced the removal efficiency of algae cells. Ultrasonic irradiation for 5 s increased the algae removal efficiency by more than 20% when the coagulant dose was 0.4-0.8 mg/L. To achieve the same algae removal ratio of 90%, sonication for 5 s reduced the coagulant dose by 2/3. The optimal sonication parameters were determined as follows: sonication time of 1 s, ultrasonic power of 48 W, and solution pH of 8-9. The sound frequency had little impact on the algal removal efficiency. Ultrasonic pretreatment also significantly reduced the sample turbidity.

Ultrasonically induced degradation and detoxification of microcystin-LR (cyanobacterial toxin)

Cyanobacterial toxins (CBTs), produced by glue-green algae, are one of the most common naturally occurring toxins found in potable waters. The microcystin family of CBTs present in drinking water sources poses a considerable threat to human health. In this study, we have demonstrated that ultrasonic irradiation at 640 kHz leads to rapid degradation of microcystin-LR (MC-LR). Degradation of MC-LR present in the crude cyanobacterial extracts containing cell constituents has been studied with ultrasound under a variety of conditions. The degradation of MC-LR was demonstrated over a concentration range from 0.03 to 3.0 microM. Hydroxyl radical scavenger experiments indicate that hydroxyl radical is responsible for a significant fraction of the observed degradation, but other processes (hydrolysis/ pyrolysis) are also important. Analysis of the protein phosphatase inhibition activity of the reaction products indicates that the products from ultrasonic degradation of MC-LR do not exhibit any measurable biological activity. The results demonstrate that ultrasonic irradiation maybe an effective and practical method for the detoxification of microcystins from drinking water.

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

Ultrasonic signals propagated through medium were directly applied to unicellular cyanobacterium cell surfaces to investigate the biological effects induced by ultrasound. The gas-vacuolate cyanobacterium Microcystis aeruginosa and the gas-vacuole negative cyanobacterium Synechococcus PCC 7942 responded differently to ultrasound. When M. aeruginosa was irradiated by 1.7 MHz ultrasound at 0.6 W cm(-2) every day, it showed a decrease of nearly 65% in biomass increment, and this group's generation time increased twice as much as the control. While Synechococcus culture irradiated every day still grew as fast as the control, and its final biomass was as much as the control. The value of the electric conductivity change (Deltasigma) sharply increased in Microcystis suspension during the exposure process, which revealed more ultrasonic cavitation yield in liquid related to the gas-vacuolate cyanobacteria. The relative malondialdehyde (MDA) content, a quantitative indicator of lipid peroxidation, increased by 65% in Microcystis cells and 9% in Synechoccus cells after ultrasonic irradiation. Moreover, the membrane permeability, quantified by measuring the relative amount of electrolyte leaking out of cells, increased to more than 60% in the Microcystis cells. The results indicated that Microcystis cells were susceptible to ultrasonic stress. According to Rayleigh-Plesset's bubble activation theory, 1.7 MHz ultrasound approached the eigenfrequency of gas-vacuolate cells. The present investigation suggested the importance of the cavitational effect relative to intracellular gas-vacuoles in the loss of cell viability. In summary, 1.7 MHz ultrasonic irradiation was effective in preventing water-bloom forming cyanobacteria from growing rapidly due to changes in the functioning and integrity of cellular and subcellular structures.

Cyanobacterial bloom control by ultrasonic irradiation at 20 kHz and 1.7 MHz

Ultrasonic irradiations at high frequency of 1.7 MHz and low frequency of 20 kHz were tested to prevent cyanobacteria Spirulina platensis from bloom. The inhibition effectiveness at 1.7 MHz was much greater than that at 20 kHz. The cyanobacteria biomass was reduced by 63% after 5 min ultrasonic irradiation at 1.7 MHz, whereas three days were needed for the tested cyanobacteria to recover its original density. However, longer exposure time did not significantly enhance the inhibition. It was observed after ultrasonic irradiation that the gas vesicles in cells collapsed, which may result in cyanobacterial precipitation and photosynthetic inhibition. The concentration of chlorophyll a (Chla) was reduced and its biosynthesis was delayed in a 4-day continuous culture. The fluorescence spectra at 77K of phycobilisome (PBS) and absorption spectra of intact cells in vivo showed that light energy transfer in PBS was inhibited and phycocyanin (PC) was damaged much more acutely compared with Chla. These results indicated that 5 min ultrasonic irradiation at 1.7 MHz every third day might be an effective and economic operation mode for practical application.

Growth inhibition of Cyanobacteria by ultrasonic radiation: laboratory and enclosure studies

The growth of Microcystis aeruginosa UTEX 2388 was repressed by ultrasonic radiation and resulted in an increased chlorophyll a content and cell size, suggesting the inhibition of cell division. However, growth was recovered immediately after the interruption of ultrasonication. In addition to the disruption of gas vesicles, other mechanisms of growth inhibition were also investigated. Although free radicals were produced by ultrasonication and hydrogen peroxide, the resulting lipid peroxidation in the cells was not comparable, indicating minimal damage by the free radicals. Ultrasonic radiation late in the day was found to be most effective in reducing the growth rate of M. aeruginosa, and this timing also corresponded to the phase of daily cell division. In an enclosure experiment, ultrasonic radiation reduced the pH, DO, total nitrogen, and total phosphorus, whereas it increased the water temperature, conductivity, and orthophosphate concentration. The algal cell density and chlorophyll a concentration drastically decreased after 3 d of ultrasonication, plus the cyanobacterial proportion was selectively reduced as compared to other algal species. Accordingly, ultrasonic radiation would appear to have considerable potential as an effective control method for cyanobacterial blooms.

A novel cyanobacteriolytic bacterium, Bacillus cereus, isolated from a Eutrophic Lake

Isolation and screening of cyanobacteriolytic bacteria were carried out. Fifteen strains of cyano-bacteriolytic bacteria were isolated by the double layer method using the cyanobacterium, Microcystis, as a sole nutrient. The isolate, N-14, showing the highest cyanobacteriolytic activity was identified as Bacillus cereus based on the 16S rRNA sequence. Components among the extracellular products in the culture supernatant of B. cereus were responsible for the cyanobacteriolytic activity. Lytic assay tests of culture supernatants indicated that the major substances for lytic activity could be non-proteinaceous, and hydrophilic, heat stable, and with a molecular weight of less than 2 kDa. The highest lytic activity was obtained under alkaline conditions, indicating an advantage for the practical application of water bloom control in eutrophic lakes where the pH is usually in the alkaline region. The lytic substance of B. cereus N-14 were compared with enterotoxins and an emetic toxin produced by a pathogenic strain of B. cereus, and also with a known algicide produced by Bacillus brevis, gramicidin. From these results, the lytic substance seemed to be a novel algicide.