Release Of Cyanotoxins Research Articles

Enhancement of adsorption of cyanobacteria, Microcystisa aeruginosaby bacterial-based compounds

In the present study, algicidal bacteria cultivated in an aqueous medium were utilized as a surface modification agent to develop an efficient adsorbent for the removal of Microcystis aeruginosa. The modification considerably enhanced M. aeruginosa cell removal efficiency. Moreover, the introduction of bio-compounds ensured specificity in the removal of M. aeruginosa. Additionally, the cyanotoxin release and acute toxicity tests demonstrated that the adsorption process using the developed adsorbent is environmentally safe. Furthermore, the practical feasibility of the adsorptive removal of M. aeruginosa was confirmed through cell removal tests performed using the developed adsorbent in a scaled-up reactor (50 L and 10 tons). In these tests, the effects of the adsorbent application type, water temperature, and initial cell concentration on the M. aeruginosa removal efficiency were evaluated. The results of this study provide novel insights into the valorization strategy of biological algicides repurposed as adsorbents, and provide practical operational data for effective M. aeruginosa removal in scaled-up conditions.

Highly efficient photocatalytic degradation of microcystin-LR with permonosulfate activated by visible-light over Z-scheme ZnO/g-C3N4: Degradation pathways and mechanism

Harmful algal blooms and the release of cyanotoxins pose a significant threat to aquatic life. This study aimed to develop a high efficient way to degrade microcystin-LR (MC-LR), a most common and highly toxic cyanotoxin in cyanobacterial blooms, by constructing a Z-scheme ZnO-g-C3N4 heterojunction for photocatalysis integrated with permonosulfate (PMS) activation process. The formation of the Z-scheme heterojunction facilitated the separation of photogenerated carriers and generated more active species with strong oxidative potential, resulting in more efficient degradation of MC-LR. Under visible light, the ZnO/g-C3N4/PMS photocatalyst successfully removed 97% of MC-LR (500 µg·L−1) within 120 min. In comparison, the ZnO/g-C3N4/PMS (k = 0.074 min−1) system exhibited degradation rate constants of 8.6 and 11.7 times higher than that of g-C3N4/PMS (k = 0.0086 min−1) and ZnO/PMS (k = 0.0063 min−1) systems, respectively. Chemical trapping experiments and EPR tests revealed that the predominant active species were •O2−, SO4•-, and •OH. The degradation route of MC-LR by ZnO/g-C3N4/PMS/Vis process was proposed based on the intermediate products analysis by UPLC-MS, wherein the addition of •OH and the oxidative cleavage by •O2− and SO4•- were the main degradation pathways. This study developed a prospective way to design Z-scheme heterojunction photocatalyst constructing with PMS activation for highly efficient prevention of harmful algal blooms.

Effect of three commercial algaecides on cyanobacteria and microcystin-LR: implications for drinking water treatment using activated carbon.

Toxic cyanobacterial blooms in aquatic ecosystems are associated to both public health and environmental concerns worldwide. Depending on the treatment technologies used, the removal capacity of cyanotoxins by drinking water treatment plants (DWTPs) is not sufficient to reach safe levels in drinking water. Likewise, controlling these blooms with algaecide may impair the efficiency of DWTPs due to the possible lysis of cyanobacterial cells and consequent release of cyanotoxins. We investigated the effects of three commercial algaecides (cationic polymer, copper sulfate, and hydrogen peroxide) on the growth parameters of the cyanobacterium Microcystis aeruginosa and the release of microcystin-LR (MC-LR). The potential interference of each algaecide on the MC-LR removal by adsorption on activated carbon (AC) was also tested through adsorption isotherms and kinetics experiments. Most algaecides significantly decreased the cell density and biovolume of M. aeruginosa, as well as increased the release of MC-LR. Interestingly, the presence of the algaecides in binary mixtures with MC-LR affected the adsorption of the cyanotoxin. Relevant adsorption parameters (e.g., maximum adsorption capacity, adsorption intensity, and affinity between MC-LR and AC) were altered when the algaecides were present, especially in the case of the cationic polymer. Also, the algaecides influenced the kinetics (e.g., by shifting the initial adsorption and the desorption constant), which may directly affect the design and operation of DWTPs. Our study indicated that algaecides can significantly impact the fate and the removal of MC-LR in DWTPs when the adsorption process is employed, with important implications for the management and performance of such facilities.

Monitoring and forecasting cyanobacteria risk for a drinking water plant in Spain

Abstract Cyanobacterial harmful algal blooms are a critical risk for public health since the release of cyanotoxins can reach hazardous levels in drinking water. In this study, a cost-effective monitoring programme has been developed and applied by a Spanish water operator to detect cyanobacteria presence in a drinking water plant reservoir; a total of 65 phytoplankton genera and seven cyanobacterial taxa were identified. Based on these monitoring data, different analysis techniques such as classification trees have been used to identify the potential situations of risk and to forecast cyanobacteria evolution in surface water. As a result, a new operational risk management plan has been developed and applied by the water operator since 2019. The main improvements concern the classification of the situations of risk in six groups (from low to very high, according to chlorophyl-a and cyanobacteria concentrations), the planning of the actions required under each situation (monitoring, management practice and treatment), and the use of the risk forecast to perform some of these actions from 2–3 days in advance. The methodology can be replicated to other case studies to facilitate the management of cyanobacteria risk and comply with the requirements of the revised European Drinking Water Directive adopted in 2020.

Evidence-Based Framework to Manage Cyanobacteria and Cyanotoxins in Water and Sludge from Drinking Water Treatment Plants.

Freshwater bodies and, consequently, drinking water treatment plants (DWTPs) sources are increasingly facing toxic cyanobacterial blooms. Even though conventional treatment processes including coagulation, flocculation, sedimentation, and filtration can control cyanobacteria and cell-bound cyanotoxins, these processes may encounter challenges such as inefficient removal of dissolved metabolites and cyanobacterial cell breakthrough. Furthermore, conventional treatment processes may lead to the accumulation of cyanobacteria cells and cyanotoxins in sludge. Pre-oxidation can enhance coagulation efficiency as it provides the first barrier against cyanobacteria and cyanotoxins and it decreases cell accumulation in DWTP sludge. This critical review aims to: (i) evaluate the state of the science of cyanobacteria and cyanotoxin management throughout DWTPs, as well as their associated sludge, and (ii) develop a decision framework to manage cyanobacteria and cyanotoxins in DWTPs and sludge. The review identified that lab-cultured-based pre-oxidation studies may not represent the real bloom pre-oxidation efficacy. Moreover, the application of a common exposure unit CT (residual concentration × contact time) provides a proper understanding of cyanobacteria pre-oxidation efficiency. Recently, reported challenges on cyanobacterial survival and growth in sludge alongside the cell lysis and cyanotoxin release raised health and technical concerns with regards to sludge storage and sludge supernatant recycling to the head of DWTPs. According to the review, oxidation has not been identified as a feasible option to handle cyanobacterial-laden sludge due to low cell and cyanotoxin removal efficacy. Based on the reviewed literature, a decision framework is proposed to manage cyanobacteria and cyanotoxins and their associated sludge in DWTPs.

Mitigation of Cyanobacterial Harmful Algal Blooms (cHABs) and Cyanotoxins by Electrochemical Oxidation: From a Bench-Scale Study to Field Application

Cyanobacterial harmful algal blooms (cHABs) and the concurrent release of cyanotoxins have become an emerging threat to aquatic life and drinking water safety. It is challenging for conventional water treatment infrastructures to mitigate cHAB events that occur frequently and irregularly. This study developed an emergency-responsive electrochemical oxidation and filtration (EOF) process that enables the pump-and-treat of phytoplankton plumes and cyanotoxins. Fundamental studies indicate that the EOF process generated locally concentrated free chlorine (>16 times higher than the bulk chlorine concentration) at the porous Ti4O7 filter anode surface. Lab tests showed that cyanobacteria and the cyanotoxin microcystin-LR were inactivated and destroyed by free chlorine when passing through the porous anode. Additionally, the concentration of disinfection byproducts generated by EOF was five times less than chlorination to achieve the same level of treatment. A boat-mount full-scale EOF system was developed and deployed in Lake Neatahwanta impacted by cHAB. The system can effectively remove >50% of phytoplankton and >80% of the ambient cyanotoxins at a treatment capacity of 110 m3/day and energy consumption of 1.1 kWh/m3. Instant improvement of effluent water clarity was achieved.

A critical review on operation and performance of source water control strategies for cyanobacterial blooms: Part I-chemical control methods

Cyanobacterial blooms produce nuisance metabolites (e.g., cyanotoxins and T&O compounds) thereby posing water quality management issues for aquatic sources used for potable water production, aquaculture, and recreation. A variety of in-lake/reservoir control measures are implemented to reduce the abundance of nuisance cyanobacteria biomass or decrease the amount of available phosphorous (P). This paper critically reviews the chemical control strategies implemented for in-lake/reservoir management of cyanobacterial blooms, i.e., algaecides and nutrient sequestering coagulants/flocculants, by highlighting (i) their mode of action, (ii) cases of successful and unsuccessful treatment, (iii) and factors influencing performance (e.g., water quality, process control techniques, source water characteristics, etc.). Algaecides generally result in immediate improvements in water quality and offer selective cyanobacterial control when peroxide-based alagecides are used. However, they have a range of limitations: causing cell lysis and release of cyanotoxins, posing negative impacts on aquatic plants and animals, leaving behind environmentally relevant treatment residuals (e.g., Cu in water and sediments), and offering only short-term bloom control characterized by cyanobacterial rebound. Coagulants/flocculants (alum, iron, calcium, and lanthanum bentonite) offer long-term internal nutrient control when external nutrient loading is controlled. Treatment performance is often influenced by background water quality conditions, and source water characteristics (e.g., surface area, depth, mixing regimes, and residence time). The reviewed case studies highlight that external nutrient load reduction is the most fundamental aspect of cyanobacterial control. None of the reviewed control strategies provide a comprehensive solution to cyanobacterial blooms.

Self-floating photocatalytic hydrogel for efficient removal of Microcystis aeruginosa and degradation of microcystins-LR

Cyanobacterial harmful algal blooms (CyanoHABs) and the release of cyanotoxins have posed adverse impacts to aquatic system and human health. In this study, a novel self-floating Ag/AgCl@LaFeO3 (ALFO) photocatalytic hydrogel was prepared via freeze-thaw method for removal of Microcystis aeruginosa (M. aeruginosa). The ALFO hydrogel performed an excellent photocatalytic activity with a 99.4% removal efficiency of chlorophyll a within 4 h. It can still remove above 95% chlorophyll a after six consecutive recycles. Besides it has also shown excellent mechanical strength and elasticity, which can ensure its use in practical applications. The mechanisms of M. aeruginosa inactivation are attributed to •O2− and •OH generated by the ALFO hydrogel under visible light radiation. In addition, •O2− and •OH can further oxidative degrade and even mineralize the leaked algae organic matter, avoiding the recurrence of CyanoHABs. What's more, the ALFO hydrogel owns good photocatalytic degradation performance for microcystins-LR (MC-LR) with a 97% removal efficiency within 90 min. A possible photocatalytic degradation pathway of MC-LR was proposed through the identification of the intermediate products during the photocatalytic reaction, which confirmed the reduction of MC-LR toxicity. This work develops recyclable a self-floating ALFO hydrogel to simultaneously inactivate M. aeruginosa and degrade MC-LR, providing a prospective method for governing and controlling CyanoHABs in practical application.

The link between pharmaceuticals and cyanobacteria: a review regarding ecotoxicological, ecological, and sanitary aspects

Cyanobacteria are important for ecosystem functioning, but eutrophication may affect the surrounding biome by losing ecosystem services and/or through affecting the cyanotoxins production that threatens ecological and human health. Pollution is an environmental issue that affects aquatic ecosystems worldwide, and the knowledge of the role of synthetic chemicals such as pharmaceuticals is still scarce. Therefore, studies coupling these two relevant issues are essential to better understand the ecological risks and the potential threats to public health. Thus, an overview of ecotoxicological tests performed in the literature exposing cyanobacteria to pharmaceuticals and the possible consequences regarding ecological and sanitary aspects was conducted. Moreover, a risk assessment was performed to enable a better understanding of pharmaceuticals affecting cyanobacteria ecology. Most of the studies found in the literature tested isolated pharmaceuticals in laboratory conditions, while others assessed mixture effects on in situ conditions. The endpoints most assessed were growth, photosynthesis, and antioxidant enzyme activity. The studies also point out that cyanobacteria may present resistance or sensitivity depending on the concentrations and the therapeutic class, which may cause a change in the ecosystem dynamics and/or sanitary implications due to cyanotoxin production. The risk assessment highlighted that antibiotics are among the most relevant substances due to the chemical diversity and higher levels found in the environment than other therapeutic classes. This review highlighted gaps regarding cyanotoxin release into aquatic environments due to the occurrence of pharmaceuticals and the need for more realistic experiments to better understand the potential consequences for human and environmental health.

Potential Impacts on Treated Water Quality of Recycling Dewatered Sludge Supernatant during Harmful Cyanobacterial Blooms.

Cyanobacterial blooms and the associated release of cyanotoxins pose problems for many conventional water treatment plants due to their limited removal by typical unit operations. In this study, a conventional water treatment process consisting of coagulation, flocculation, sedimentation, filtration, and sludge dewatering was assessed in lab-scale experiments to measure the removal of microcystin-LR and Microcystis aeruginosa cells using liquid chromatography with mass spectrometer (LC-MS) and a hemacytometer, respectively. The overall goal was to determine the effect of recycling cyanotoxin-laden dewatered sludge supernatant on treated water quality. The lab-scale experimental system was able to maintain the effluent water quality below relevant the United States Environmental Protection Agency (US EPA) and World Health Organisation (WHO) standards for every parameter analyzed at influent concentrations of M. aeruginosa above 106 cells/mL. However, substantial increases of 0.171 NTU (Nephelometric Turbidity Unit), 7 × 104 cells/L, and 0.26 µg/L in turbidity, cyanobacteria cell counts, and microcystin-LR concentration were observed at the time of dewatered supernatant injection. Microcystin-LR concentrations of 1.55 µg/L and 0.25 µg/L were still observed in the dewatering process over 24 and 48 h, respectively, after the initial addition of M. aeruginosa cells, suggesting the possibility that a single cyanobacterial bloom may affect the filtered water quality long after the bloom has dissipated when sludge supernatant recycling is practiced.

Toxicity of chlorinated algal-impacted waters: Formation of disinfection byproducts vs. reduction of cyanotoxins

Seasonal algal blooms in surface waters can impact water quality through an input of algal organic matter (AOM) to the pool of dissolved organic matter as well as the release of cyanotoxins. The formation and speciation of disinfection byproducts (DBPs) during chlorination of algal-impacted waters, collected from growth of Microcystis aeruginosa were studied. Second-order rate constants for the reactions of microcystins (MCs) with chlorine and bromine were determined. Finally, the toxicity of chlorinated algal-impacted waters was evaluated by Chinese hamster ovary (CHO) cytotoxicity and genotoxicity assays. Under practical water treatment conditions, algal-impacted waters produced less regulated trihalomethanes (THMs) and haloacetic acids (HAAs), haloacetonitriles (HANs), and total organic halogen (TOX) than natural organic matter (NOM). For example, the weight ratios of DBP formation from AOM to NOM (median levels) were approximately 1:5, 1:3, 1:2 and 1:3 for THMs, HAAs, HANs, and TOX, respectively. Increasing initial bromide level significantly enhanced THM and HAN concentrations, and therefore unknown TOX decreased. The second-order rate constant for the reactions of MC-LR (the most common MC species) with chlorine was 60 M−1 s−1 at pH 7.5 and 21 °C, and the rate constants for MC congeners follow the order: MC-WR > MC-LW > MC-YR > MC-LY > MC-LR ≈ MC-RR. The reaction rate constant of bromine with MC-LR is two orders of magnitude higher than that of chlorine. Unchlorinated algal-impacted waters were toxic owning to the presence of MCs, and chlorination enhanced their cytotoxicity and genotoxicity due to the formation of toxic halogenated DBPs. However, the toxicity of treated waters depended on the evolution of cyanotoxins and formation of DBPs (particularly unknown or emerging DBPs).

Adsorption Strategy for Removal of Harmful Cyanobacterial Species Microcystis aeruginosa Using Chitosan Fiber

Microcystis aeruginosa is one of the predominant species responsible for cyanobacterial-harmful algal blooms (Cyano-HABs) in water bodies. Cyano-HABs pose a growing number of serious threats to the environment and public health. Therefore, the demand for developing safe and eco-friendly solutions to control Cyano-HABs is increasing. In the present study, the adsorptive strategy using chitosan was applied to remove M. aeruginosa cells from aqueous phases. Using a simple immobilization process, chitosan could be fabricated as a fiber sorbent (chitosan fiber, CF). By application of CF, almost 89% of cyanobacterial cells were eliminated, as compared to those in the control group. Field emission scanning electron microscopy proved that the M. aeruginosa cells were mainly attached to the surface of the sorbent, which was correlated well with the measurement of the surface area of the fiber. We tested the hypothesis that massive applications of the fabricated CF to control Cyano-HABs might cause environmental damage. However, the manufactured CF displayed negligible toxicity. Moreover, we observed that the release of cyanotoxins and microcystins (MCs), during the removal process using CF, could be efficiently prevented by a firm attachment of the M. aeruginosa cells without cell lysis. Our results suggest the possibility of controlling Cyano-HABs using a fabricated CF as a non-toxic and eco-friendly agent for scaled-up applications.

The Impacts of Potassium Permanganate and Powdered Activated Carbon on Cyanotoxin Release.

Bench-scale trials were performed to: (1) Expose Microcystis aeruginosa cells to potassium permanganate doses of 1, 3 and 5 mg/L, at contact times of 15, 30 and 90 minutes, pH levels of 7 and 9, and turbidities of 0.1, 5 and 20 NTU; (2) Compare the impacts of oxidation alone and oxidation plus powdered activated carbon for the final 60 minutes of contact time and (3) evaluate the impact of these treatment conditions on extracellular microcystins, extra- plus intracellular (combined) microcystins, cell membrane integrity and chlorophyll-a concentrations. Toxin releases from the cells were observed at both pH levels. The greatest toxin releases were observed at the lowest KMnO4 doses. The toxin releases were accompanied by relatively stable total cell counts, increases in membrane compromised cells and decreases in chlorophyll-a. The application of 10 mg/L PAC resulted in extracellular toxin concentrations that were markedly lower than those observed in oxidant-only situations.

Bacteria as biological control agents of freshwater cyanobacteria: is it feasible beyond the laboratory?

Biological control of cyanobacteria is a well-researched area with a central focus on laboratory-scale studies. Numerous reports have been made on algicidal isolates, with bacteria as a major component of the antagonists. The research in this review draws a brief summary of what is currently known in the area of freshwater cyanobacteria being inhibited by bacterial isolates. Proteobacteria, Bacteroidetes and Firmicutes are among the most commonly reported phyla of bacteria associated with or employed in this research area. However, there are limited reports of upscaling these control measures beyond the laboratory scale. Lytic control agents are the most commonly reported in the literature with subsequent cyanotoxin release. From a water quality perspective, this is not feasible. Based on the available literature, temperature, pH and nutrient changes have been explored in this short review as possible contributors to less optimal bacterial performance. Moreover, the investigation into optimising some of these parameters may lead to increased bacterial performance and, therefore, viability for upscaling this biological control. Through the compilation of current research, this review offers insight to live predator-prey cell interactions between cyanobacteria and algicidal bacteria.

Recycled desalination membranes as a support material for biofilm development: A new approach for microcystin removal during water treatment

Increased harmful cyanobacterial blooms and drought are some negative impacts of global warming. To deal with cyanotoxin release during water treatment, and to manage the massive quantities of end-of-life membrane waste generated by desalination processes, we propose an innovative biological system developed from recycled reverse osmosis (RO) membranes to remove microcystins (MC). Our system, named the Recycled-Membrane Biofilm Reactor (R-MBfR), effectively removes microcystins, while reducing the pollution impact of RO membrane waste by prolonging their life span at the same time. This multidisciplinary work showed that the inherent flaw of RO membranes, i.e., fouling, can be considered an advantageous characteristic for biofilm attachment. Factors such as roughness, hydrophilic surfaces, and the role of calcium in cell-cell and cell-surface interactions, encouraged bacterial growth on discarded membranes. Biofilm development was stimulated by using a laboratory-scale membrane module simulator cell. The R-MBfR proved versatile and was capable of degrading 2 mg·L−1 of MC in 24 h. The economic feasibility of the scaling-up of the hypothetical R-MBfR was also validated. Therefore, this membrane recycling could be a future green cost-effective alternative technology for MC removal.

The efficiency of combined coagulant and ballast to remove harmful cyanobacterial blooms in a tropical shallow system

We tested the hypothesis that a combination of coagulant and ballast could be efficient for removal of positively buoyant harmful cyanobacteria in shallow tropical waterbodies, and will not promote the release of cyanotoxins. This laboratory study examined the efficacy of coagulants [polyaluminium chloride (PAC) and chitosan (made of shrimp shells)] alone, and combined with ballast (lanthanum modified bentonite, red soil or gravel) to remove the natural populations of cyanobacteria collected from a shallow eutrophic urban reservoir with alternating blooms of Cylindrospermopsis and Microcystis. PAC combined with ballast was effective in settling blooms dominated by Microcystis or Cylindrospermopsis. Contrary to our expectation, chitosan combined with ballast was only effective in settling Cylindrospermopsis-dominated blooms at low pH, whereas at pH≥8 no effective flocculation and settling could be evoked. Chitosan also had a detrimental effect on Cylindrospermopsis causing the release of saxitoxins. In contrast, no detrimental effect on Microcystis was observed and all coagulant-ballast treatments were effective in not only settling the Microcystis dominated bloom, but also lowering dissolved microcystin concentrations. Our data show that the best procedure for biomass reduction also depends on the dominant species.

Spatiotemporal Dynamics of Microcystin Variants and Relationships with Environmental Parameters in Lake Taihu, China.

Excessive anthropogenically-caused nutrient loading from both external and internal sources has promoted the growth of cyanobacteria in Lake Taihu from 2005 to 2014, suggesting increased production and release of cyanotoxins. In order to explain the spatial distribution and temporal variation of microcystins (MCs), the intracellular concentrations of MCs (MC-LR, -RR and -YR, L, R and Y are abbreviations of leucine, arginine and tyrosine) were monitored monthly from July 2013 to June 2014. Three MC variants are present simultaneously in Lake Taihu; the MC-LR and -RR variants were dominant (accounting for 40% and 39% of the total), followed by MC-YR (21%). However, MC-YR accounted for a higher proportion in colder months, especially in March. The highest concentrations of intracellular MCs were found in July and October when cyanobacteria cell density also reached the maximum. The average concentrations of MC-LR, -RR and -YR in July were 4.69, 4.23 and 2.01 μg/L, respectively. In terms of the entire lake, toxin concentrations in northern parts were significantly higher than the eastern part in summer, when MC concentrations were several times higher than the guideline value by WHO throughout much of Lake Taihu. Results from correlation and redundancy analysis (RDA) showed that total MCs, including all variants, were strongly and positively correlated with cyanobacteria cell density, water temperature, total phosphorus (TP) and pH, whereas each variant had different correlation coefficients with each of the considered environmental variables. MC-RR showed a stronger relationship with temperature, in contrast to MC-YR and -LR. Dissolved inorganic carbon (DIC) showed a negative relationship with each variant, suggesting that rising DIC concentrations may inhibit cyanobacterial growth and thereby reduce MC production in the future.

Mitigating harmful cyanobacterial blooms in a human- and climatically-impacted world.

Bloom-forming harmful cyanobacteria (CyanoHABs) are harmful from environmental, ecological and human health perspectives by outcompeting beneficial phytoplankton, creating low oxygen conditions (hypoxia, anoxia), and by producing cyanotoxins. Cyanobacterial genera exhibit optimal growth rates and bloom potentials at relatively high water temperatures; hence, global warming plays a key role in their expansion and persistence. CyanoHABs are regulated by synergistic effects of nutrient (nitrogen:N and phosphorus:P) supplies, light, temperature, vertical stratification, water residence times, and biotic interactions. In most instances, nutrient control strategies should focus on reducing both N and P inputs. Strategies based on physical, chemical (nutrient) and biological manipulations can be effective in reducing CyanoHABs; however, these strategies are largely confined to relatively small systems, and some are prone to ecological and environmental drawbacks, including enhancing release of cyanotoxins, disruption of planktonic and benthic communities and fisheries habitat. All strategies should consider and be adaptive to climatic variability and change in order to be effective for long-term control of CyanoHABs. Rising temperatures and greater hydrologic variability will increase growth rates and alter critical nutrient thresholds for CyanoHAB development; thus, nutrient reductions for bloom control may need to be more aggressively pursued in response to climatic changes globally.

Effects of hydrogen peroxide and ultrasound on biomass reduction and toxin release in the cyanobacterium, Microcystis aeruginosa.

Cyanobacterial blooms are expected to increase, and the toxins they produce threaten human health and impair ecosystem services. The reduction of the nutrient load of surface waters is the preferred way to prevent these blooms; however, this is not always feasible. Quick curative measures are therefore preferred in some cases. Two of these proposed measures, peroxide and ultrasound, were tested for their efficiency in reducing cyanobacterial biomass and potential release of cyanotoxins. Hereto, laboratory assays with a microcystin (MC)-producing cyanobacterium (Microcystis aeruginosa) were conducted. Peroxide effectively reduced M. aeruginosa biomass when dosed at 4 or 8 mg L−1, but not at 1 and 2 mg L−1. Peroxide dosed at 4 or 8 mg L−1 lowered total MC concentrations by 23%, yet led to a significant release of MCs into the water. Dissolved MC concentrations were nine-times (4 mg L−1) and 12-times (8 mg L−1 H2O2) higher than in the control. Cell lysis moreover increased the proportion of the dissolved hydrophobic variants, MC-LW and MC-LF (where L = Leucine, W = tryptophan, F = phenylalanine). Ultrasound treatment with commercial transducers sold for clearing ponds and lakes only caused minimal growth inhibition and some release of MCs into the water. Commercial ultrasound transducers are therefore ineffective at controlling cyanobacteria.

Anti-algal activity of palladium oxide-modified nitrogen-doped titanium oxide photocatalyst on Anabaena sp. PCC 7120 and its photocatalytic degradation on Microcystin LR under visible light illumination

Blue algae blooms could cause the indiscriminate killing of fish/invertebrates in water and the destruction of the local ecological equilibrium. The release of cyanotoxins by blue algae cells could kill livestock and cause various health problems to human beings. The highly effective photocatalytic disinfection of Anabaena sp. PCC 7120 as a representative blue algae specie under visible light illumination was demonstrated on a visible-light-activated palladium oxide-modified nitrogen-doped titanium oxide (TiON/PdO) nanoparticle photocatalyst. The large release of substances in blue algae cells, such as chlorophyll a and various ions, and severe damages on their cell wall/membrane clearly demonstrated the photocatalytic disinfection on blue algae by TiON/PdO nanoparticles under visible light illumination was an irreversible process. TiON/PdO nanoparticles also demonstrated a highly efficient photocatalytic degradation of a typical cyanotoxin, Microcystin LR, under visible light illumination. Thus, the photocatalytic treatment by TiON/PdO nanoparticles could effectively disinfect blue algae and degrade cyanotoxins under visible light illumination at the same time, which makes it attractive as an environmentally friendly and cost-effective alternative to current blue algae treatment practices.