Microcystin analysis in single filaments of Planktothrix spp. in laboratory cultures and environmental blooms

Single filaments of Planktothrix spp. were isolated from laboratory cultures of P. agardhii (NIES 595) and P. rubescens (SL 03) and from four freshwater lakes in England and Turkey. Filament lengths were measured and microcystins were extracted by freeze-thawing and boiling. Microcystin analysis of the isolated single filaments was performed by ELISA using antibodies raised against microcystin-LR with a minimum detection limit (MDL) of 11 pg filament(-1). In some cases a high percentage of the filaments from the environmental samples and laboratory cultures were below the MDL of the assay. Based on the filaments with detectable microcystin contents, P. agardhii from Bassenthwaite Lake (England) had the lowest mean microcystin concentration (0.7 fg microm(-3)), and the highest microcystin concentration (2.9 fg microm(-3)) was measured in P. rubescens from Iznik Lake (Turkey). We investigated the relationship for filaments with microcystin contents above MDL and their biovolume. Relationships varied widely although P. agardhii from Bassenthwaite showed a better (positive) relationship between filament biovolume and microcystin content than P. rubescens from environmental samples. Under culture conditions, P. rubescens showed a good relationship between filament biovolume and toxin content.     

Treatment of drinking water residuals: comparing sedimentation and dissolved air flotation performance with optimal cation ratios

Spent filter backwash water (SFBW) and clarifier sludge generally comprise the majority of the waste residual volume generated and in relative terms, these can be collectively referred to as combined filter backwash water (CFBW). CFBW is essentially a low-solids wastewater with metal hydroxide flocs that are typically light and slow to settle. This study evaluates the impact of adding calcium and magnesium carbonates to CFBW in terms of assessing the impacts on the sedimentation and DAF separation processes. Representative CFBW samples were collected from two surface water treatment plants (WTP): Lake Major WTP (Dartmouth, Nova Scotia, Canada) and Victoria Park WTP (Truro, Nova Scotia, Canada). Bench-scale results indicated that improvements in the CFBW settled water quality could be achieved through the addition of the divalent cations, thereby adjusting the monovalent to divalent (M:D) ratios of the wastewater. In general, the DAF process required slightly higher M:D ratios than the sedimentation process. The optimum M:D ratios for DAF and sedimentation were determined to be 1:1 and 0.33:1, respectively. It was concluded that the optimisation of the cation balance between monovalent cations (e.g., Na(+), K(+)) and added divalent cations (i.e., Ca(2+), Mg(2+)) aided in the settling mechanism through charge neutralisation-precipitation. The increase in divalent cation concentrations within the waste residual stream promoted destabilisation of the negatively charged colour molecules within the CFBW, thereby causing the colloidal content to become more hydrophobic.     

Dissolved air flotation and me

This paper is mainly a critical review of the literature and an assessment of what we know about dissolved air flotation (DAF). A few remarks are made at the outset about the author's personal journey in DAF research, his start and its progression. DAF has been used for several decades in drinking water treatment as an alternative clarification method to sedimentation. DAF is particularly effective in treating reservoir water supplies; those supplies containing algae, natural color or natural organic matter; and those with low mineral turbidity. It is more efficient than sedimentation in removing turbidity and particles for these type supplies. Furthermore, it is more efficient in removing Giardia cysts and Cryptosporidium oocysts. In the last 20 years, fundamental models were developed that provide a basis for understanding the process, optimizing it, and integrating it into water treatment plants. The theories were tested through laboratory and pilot-plant studies. Consequently, there have been trends in which DAF pretreatment has been optimized resulting in better coagulation and a decrease in the size of flocculation tanks. In addition, the hydraulic loading rates have increased reducing the size of DAF processes. While DAF has been used mainly in conventional type water plants, there is now interest in the technology as a pretreatment step in ultrafiltration membrane plants and in desalination reverse osmosis plants.     

Surface-retained organic matter of Microcystis aeruginosa inhibiting coagulation with polyaluminum chloride in drinking water treatment

Algogenic organic matter produced by the excess growth of cyanobacteria in semi-closed water areas causes coagulation inhibition in drinking water production. In this study, hydrophilic substances of Microcystis aeruginosa, which were mainly composed of lipopolysaccharide (LPS) and RNA, were prepared, and the involvement of these cyanobacterial hydrophilic substances in coagulation inhibition was investigated. As a result, it was found that the negatively charged hydrophilic substances with a molecular weight higher than 10 kDa have a significant role in coagulation inhibition. Further fractionation of cyanobacterial hydrophilic substances revealed that surface-retained organic matter (SOM), including LPS, could exhibit a potent inhibitory effect on the coagulation using polyaluminum chloride (PACl), presumably because of the direct interaction of hydrophilic SOM with cations originated from PACl, which could impede the hydrolysis of the coagulant.     

Cellular proteins of Microcystis aeruginosa inhibiting coagulation with polyaluminum chloride

Cyanobacterial growth in semi-closed water areas such as reservoirs brings about a coagulation inhibition in a drinking water treatment system, but the inhibitory substances and mechanisms involved have yet to be elucidated. In this study, proteins having a high affinity with polyaluminum chloride (PACl) were isolated from organic substances produced by Microcystis aeruginosa with the affinity chromatography technique. Both extracellular organic matter (EOM) and cellular organic matter (COM) disturbed the flocculation of suspended kaolin with PACl, but it was likely that nonproteinous substances in EOM cause the reduction of coagulation effciency. In contrast, proteins in COM were obtained as possible inhibitory substances for the coagulation with PACl. These proteins could consume PACl in the coagulation process due to the formation of chelate complexes between these inhibitory proteins and the coagulant. The consumption of PACl by cyanobacterial proteins could be one of the important causes of the increase in coagulant demand.     

Importance of flow stratification and bubble aggregation in the separation zone of a dissolved air flotation tank

The importance of horizontal flow patterns and bubble aggregation on the ability of dissolved air flotation (DAF) systems to improve bubble removal during drinking water treatment were explored using computational fluid dynamics (CFD) modeling. Both analytical and CFD analyses demonstrated benefits to horizontal flow. Two dimensional CFD modeling of a DAF system showed that increasing the amount of air in the system improved the bubble removal and generated a beneficial stratified horizontal flow pattern. Loading rates beyond a critical level disrupted the horizontal flow pattern, leading to significantly lower bubble removal. The results also demonstrated that including the effects of bubble aggregation in CFD modeling of DAF systems is an essential component toward achieving realistic modeling results.     

Coagulation of peptides and proteins produced by Microcystis aeruginosa: Interaction mechanisms and the effect of Fe-peptide/protein complexes formation

This paper focuses on elucidation of the mechanisms involved in the coagulation of peptides and proteins contained in cellular organic matter (COM) of cyanobacterium Microcystis aeruginosa by ferric coagulant. Furthermore, coagulation inhibition due to the formation of Fe-peptide/protein surface complexes was evaluated. The results of coagulation testing imply that removability of peptides and proteins is highly dependent on pH value which determines charge characteristics of coagulation system compounds and therefore the mechanisms of interactions between them. The highest peptide/protein removal was obtained in the pH range of 4-6 owing to charge neutralization of peptide/protein negative surface by positively charged hydrolysis products of ferric coagulant. At low COM/Fe ratio (COM/Fe <0.33), adsorption of peptides/proteins onto ferric oxide-hydroxide particles, described as electrostatic patch model, enables the coagulation at pH 6-8. On the contrary, steric stabilization reduces coagulation at pH 6-8 if the ratio COM/Fe is high (COM/Fe >0.33). Coagulation of peptides and proteins is disturbed at pH 6-7 as a consequence of Fe-peptide/protein complexes formation. The maximum ability of peptides/proteins to form soluble complexes with Fe was found just at pH 6, when peptides/proteins bind 1.38 mmol Fe per 1 g of peptide/protein DOC. Complex forming peptides and proteins of relative molecular weights of 1, 2.8, 6, 8, 8.5, 10 and 52 kDa were isolated by affinity chromatography.     

The role of nitrobenzene on the yield of trihalomethane formation potential in aqueous solutions with Microcystis aeruginosa

Algae are one of the most important disinfection by-product (DBP) precursors in aquatic environments. The contents of DBP precursors in algae are influenced by not only environmental factors but also some xenobiotics. Trihalomethane formation potential (THMFP) in both the separate and interactive pollution of Microcystis aeruginosa and Nitrobenzene (NB) was investigated in batch experiment to discover the effects of xenobiotics on the yield of DBP precursors in the algal solution. The results show that in the separate NB solution, NB did not react with Cl₂ to form trihalomethane (THM), whereas in the algae solution, THMFP had a significant positive linear correlation with M. aeruginosa density in both solution and extracellular organic matter (EOM). The correlation coefficients were 0.9845 (p = 3.567 × 10⁻⁴) and 0.9854 (p = 1.406 × 10⁻⁴), respectively. According to regression results, about 77.9% of the total THMFP came from the algal cells, while the rest came from EOM. When the interactive pollution of M. aeruginosa and NB occurred, the growth of algae was inhibited by NB. The density of M. aeruginosa in a high concentration NB solution (280 μg/L) was only 71.1% of that in the solution without NB after 5 days of incubation. However, THMFP in the mixture (algae and NB) and the EOM did not change significantly, and the productivity of THMFP by the algae (THMFP/10⁸cells) increased with the increase in NB concentration. There was a significant linear correlation between THMFP/10⁸cell and NB concentration (r = 0.9117, p < 0.01), which shows the contribution of the algae to THM formation was enhanced by NB. This result might be caused by the increased protein productivity and the biodegradation of NB by M. aeruginosa.     

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.     

UV-induced photochemical heterogeneity of dissolved and attached organic matter associated with cyanobacterial blooms in a eutrophic freshwater lake

Cyanobacterial blooms represent a significant ecological and human health problem worldwide. In aquatic environments, cyanobacterial blooms are actually surrounded by dissolved organic matter (DOM) and attached organic matter (AOM) that bind with algal cells. In this study, DOM and AOM fractionated from blooming cyanobacteria in a eutrophic freshwater lake (Lake Taihu, China) were irradiated with a polychromatic UV lamp, and the photochemical heterogeneity was investigated using fluorescence excitation–emission matrix (EEM)-parallel factor (PARAFAC) analysis and synchronous fluorescence (SF)-two dimensional correlation spectroscopy (2DCOS). It was shown that a 6-day UV irradiation caused more pronounced mineralization for DOM than AOM (59.7% vs. 41.9%). The EEM-PARAFAC analysis identified one tyrosine-, one humic-, and two tryptophan-like components in both DOM and AOM, and high component photodegradation rates were observed for DOM versus AOM (k > 0.554 vs. <0.519). Moreover, SF-2DCOS found that the photodegradation of organic matters followed the sequence of tyrosine-like > humic-like > tryptophan-like substances. Humic-like substances promoted the indirect photochemical reactions, and were responsible for the higher photochemical rate for DOM. The lower photodegradation of AOM benefited the integrality of cells in cyanobacterial blooms against the negative impact of UV irradiation. Therefore, the photochemical behavior of organic matter was related to the adaptation of enhanced-duration cyanobacterial blooms in aquatic environments.     

Analysis of dissolved microcystins in surface water samples from Kovada Lake, Turkey

Dissolved (extracellular) microcystin (MC) concentrations were determined at 3 sampling stations on Lake Kovada, Turkey. The dominant species of cyanobacteria found in August and September of 2006 were Microcystis aeruginosa, Synechococcus sp., Phormidium limosum, Phormidium formosa and Planktothrix limnetica. MC concentrations in water were measured by ELISA and MC variants were examined by HPLC-PDA. Quantitative analysis by HPLC indicated that five MC variants (MC-LR, -RR, -LA, -LW, -LF) were identified in water samples from Kovada Lake. The maximum concentration of dissolved MC-LW was 98.9 µg l^− 1 in October. MC-LR was only detected in May at a concentration of 0.5 µg l^− 1. The cross reactivity of the antibody (MC10E7) to variants such as MC-LA MC-LW & MC-LF was low. Hence the results determined by ELISA were lower than those determined by HPLC in September and October samples due to differences in the specificity of the antibody to MC variants. Total extraceullar MCs was quantified by ELISA and ranged from 0.73 to 48.5 µg MC-LR equivalents l^− 1, which in some cases exceeded the WHO provisional Guideline Value for MC-LR in drinking water. This study confirms that the lakes of Turkey should be monitored for toxic cyanobacteria and for MCs to avoid or reduce the potential exposure of people to these health hazards.     

Bio-reaction of nitrobenzene with Microcystis aeruginosa: characteristics, kinetics and application

The bio-reaction of nitrobenzene (NB) with Microcystis aeruginosa was investigated at different initial algal densities and NB concentrations by performing static experiments. The results showed that the elimination of NB was enhanced by the bio-reaction, and the reaction rate varied as a function of the reaction time. Moreover, the reaction rate was significantly affected by the algal density and NB concentration. A kinetic analysis showed that the elimination of NB in a solution without algae appeared to be pseudo-first-order with respect to the NB concentration, whereas a first-order model was too oversimplified to describe the elimination of NB in a solution with algae. Assuming that different algal cells have the same effect on the bio-reaction under the same conditions, the bio-reaction can be described as dC_NB = −k₀C_A^mA_NBⁿdt (where k₀ is the reaction rate constant, C_A is the algae density and C_NB is the concentration of NB). When the growth of algae was not considered, the value of k₀, m and n were 8.170 × 10⁻⁴, 0.5887 and 1.692, respectively. Alternatively, when algae were in the exponential growth phase, the value of k₀, m and n were 1.6871 × 10⁻⁵, 0.7248 and 2.5407, respectively, according to a nonlinear fitting analysis. The kinetic model was also used to elucidate the effect of nutritional limitation on the bio-reaction.     

铜绿微囊藻衰亡过程中产甲烷动态及关键影响因子

为探究铜绿微囊藻水华自然衰亡和水华堆积区藻快速衰亡对CH_4释放的影响,构建了室内模拟实验,研究了铜绿微囊藻自然衰亡和快速衰亡过程中水环境因子和CH_4、CO_2气体释放通量的变化。结果表明:高密度铜绿微囊藻衰亡中水环境因子和产气的变化遵循相似的时间模式,且衰亡对CH_4和CO_2的产生有显著的促进作用。自然衰亡和快速衰亡的CH_4累积释放量分别为对照组的22.80倍37.72倍,CO_2累积释放量分别为对照组的5.36倍和4.03倍。自然衰亡与快速衰亡的总碳(C)释放量差异不大,但快速衰亡释放的气体组分中CH_4的占比是自然衰亡的1.86倍。相关性分析表明,溶解性有机碳(DOC)是铜绿微囊藻衰亡中影响CH_4和CO_2释放的主导因子,且DOC中的芳香蛋白类物质和溶解性微生物代谢产物是CH_4和CO_2产生的主要底物来源。     

Coagulation of humic substances and dissolved organic matter with a ferric salt: an electron energy loss spectroscopy investigation

Transmission electron microscopy (TEM) coupled with electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDXS) was used to investigate the coagulation of natural organic matter with a ferric salt. Jar-test experiments were first conducted with a reconstituted water containing either synthetic or natural extracts of humic substances, and then with a raw water from Moselle River (France). The characterization of the freeze-dried coagulated sediment by EELS in the 250-450 eV range, showed that Fe-coagulant species predominantly associate with the carboxylic groups of organic matter, and that this interaction is accompanied by a release of previously complexed calcium ions. The variation of Fe/C elemental ratio with iron concentration provides insightful information into the coagulation mechanism of humic substances. At acid pH, Fe/C remains close to 3 over the whole range of iron concentrations investigated, while a much lower atomic ratio is expected from the value of optimal coagulant dosage. This suggests that a charge neutralization/complexation mechanism is responsible for the removal of humic colloids, the aggregates being formed with both iron-coagulated and proton-neutralized organic compounds. At pH 8, the decrease in Fe/C around optimal coagulant concentration is interpreted as a bridging of stretched humic macromolecules by Fe-hydrolyzed species. Aggregation would then result from a competition between reconformation of humic chains around coagulant species and collision of destabilized humic material. EELS also enabled a fingerpriting of natural organic substances contained in the iron-coagulated surface water, N/C elemental analyses revealing that humic colloids are removed prior to proteinic compounds.     

A comparison of the role of two blue-green algae in THM and HAA formation

The contribution of two blue-green algae species, Anabaena flos-aquae and Microcystis aeruginosa, to the formation of trihalomethanes (THMs) and haloacetic acids (HAAs) was investigated. The experiments examined the formation potential of these disinfection by-products (DBPs) from both algae cells and extracellular organic matter (EOM) during four algal growth phases. Algal cells and EOM of Anabaena and Microcystis exhibited a high potential for DBP formation. Yields of total THMs (TTHM) and total HAAs (THAA) were closely related to the growth phase. Reactivity of EOM from Anabaena was slightly higher than corresponding cells, while the opposite result was found for Microcystis. Specific DBP yields (yield/unit C) of Anabaena were in the range of 2-11 μmol/mmol C for TTHM and 2-17 μmol/mmol C for THAA, while those of Microcystis were slightly higher. With regard to the distributions of individual THM and HAA compounds, differences were observed between the algae species and also between cells and EOM. The presence of bromide shifted the dominant compounds from HAAs to THMs.     

Immediate and long-term impacts of UV-C irradiation on photosynthetic capacity, survival and microcystin-LR release risk of Microcystis aeruginosa

In this study, the immediate and long-term impacts of shortwave ultraviolet (UV-C) irradiation on photosynthetic capacity, survival, and recovery of Microcystis aeruginosa were investigated. The risk of microcystin-LR (MC-LR) release during irradiation was also estimated. The cell density was determined by a flow cytometry, and typical chlorophyll fluorescence parameters, including the effective quantum yield, photosynthetic efficiency and maximal electron transport rate, were measured by a pulse amplitude modulated (PAM) fluorometer. Under various UV-C dosages (140-4200 mJ cm⁻²), photosynthetic capacities were reduced, to different degrees, accompanied by slight cytoclasis and complete degradation of extracellular MC-LR immediately after irradiation. In a 6-d cultivation following UV-C irradiation, cell density and extracellular MC-LR in the samples treated by 140 mJ cm⁻² UV-C irradiation increased from 4.0 × 10⁶ cells mL⁻¹ and 8 μg L⁻¹ to 5.1 × 10⁶ cells mL⁻¹ and 20 μg L⁻¹, respectively. Significant M. aeruginosa cytoclasis (cell density from 4.0 × 10⁶ to 1.0 × 10⁶ cells mL⁻¹) and MC-LR release (2-25 μg L⁻¹) occurred when the UV-C dosage reached 350 mJ cm⁻². Cell cytoclasis and MC-LR release were enhanced in the cultivated samples under higher UV-C dosages. Results revealed that photosynthetic parameters were useful tools to predict the recovery profiles of M. aeruginosa cells, and the MC-LR release risk should be considered after UV-C inactivation.     

Copper sulphate and DCMU-herbicide treatments increase asymmetry between sister cells in the toxic cyanobacteria Microcystis aeruginosa: implications for detecting environmental stress

Works correlating fluctuating asymmetry with environmental stress or genetic damages have been largely reported in multicellular organisms but not in single-celled ones. We hypothesize that asymmetry analysis could also be applied to single-celled organisms, because the asymmetry between two sister cells originated from a cellular division event (same genotype in similar environment) must tend to zero in the absence of environmental or genetic perturbations. Laboratory experiments with copper sulphate and DCMU-herbicide treatments as well as experiments in a water reservoir after treatment with copper sulphate algaecide show that environmental stress increases asymmetry between sister cells of Microcystis aeruginosa (Cyanobacteria). Even low Cu(2+) or DCMU doses, which were unable to reduce growth rate, considerably enlarge asymmetry with respect to untreated controls. Asymmetry between sister cells of cyanobacteria seems to be a reliable indicator of environmental perturbation. Analysis of asymmetry in single-celled organisms could become as important as fluctuating asymmetry of multicellular organisms is today.     

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.     

Occurrence of copper resistant mutants in the toxic cyanobacteria Microcystis aeruginosa: characterisation and future implications in the use of copper sulphate as algaecide

Freshwater toxic cyanobacteria are an increasing problem to human and animal health. Control of cyanobacteria in water supply reservoirs involves the use of algaecides, such as copper sulphate, usually in a repetitive way. Repercussions of recurrent algaecide treatments on cyanobacteria population dynamics remain still unknown. We studied the adaptation of cyanobacteria to lethal doses of copper sulphate by using Microcystis aeruginosa as an experimental model. A fluctuation analysis demonstrated that copper-resistant cells arise by spontaneous mutations that occur randomly prior to exposition to copper sulphate. The rate of spontaneous mutation from copper sensitivity to resistance was 1.76×10⁻⁶ mutants per cell division. Resistant mutants exhibited a diminished fitness in the absence of copper sulphate, but only these variants were able to grow at Cu²⁺ concentrations higher than 5.8 μM. In addition, copper-resistant cells were significantly smaller than wild-type ones. Warnings on the long-term consequences of repetitive algaecide treatments in water supplies are suggested.     

Effect of Pseudokirchneriella subcapitata (Chlorophyceae) exudates on metal toxicity and colloid aggregation

The effects of Pseudokirchneriella subcapitata exudates on the acute toxicity of metals (Cd, Cu, Pb and Zn) were studied using (1h) algal photosynthesis inhibition tests. The metal concentrations tested were 30, 60, 120, 250 and 500microgL(-1) for Cd and Zn; and 500, 1000, 2000, 3000, 4000microgL(-1) for Cu and Pb. It was established that P. subcapitata exudates markedly decreased metal toxicity. This effect was ascribed to: (i) the presence of organic ligands that bind metals and reduce the concentration of free ionic metal, and/or (ii) interaction of exudates with the cell surface with a subsequent decrease in metal uptake. The effects of the exudates on colloid aggregation were also examined using two different types of single particle counters (SPC). Exudates facilitated the colloid removal, likely via acceleration of aggregation (bridging). The results clearly demonstrate that algal exudates play an important role in the biogeochemical cycling of metals in natural surface water: (1) by reducing free metal concentrations and toxicity to living organisms and (2) by favoring colloid aggregation leading to the removal of colloid-bound metals (colloidal pumping). Such results highlight one potential application of the algae in the remediation of metal-contaminated waters. The results also suggest that current algal toxicity testing protocols, in particular long-term and static tests, may underestimate metal toxicity because of the presence of algal exudates.