Zhengqiu Fan

Isolation and algae-lysing characteristics of the algicidal bacterium B5

Water blooms have become a worldwide environmental problem. Recently, algicidal bacteria have attracted wide attention as possible agents for inhibiting algal water blooms. In this study, one strain of algicidal bacterium B5 was isolated from activated sludge. On the basis of analysis of its physiological characteristics and 16S rDNA gene sequence, it was identified as Bacillus fusiformis. Its algaelysing characteristics on Microcystis aeruginosa, Chlorella and Scenedesmus were tested. The results showed that: (1) the algicidal bacterium B5 is a Gram-negative bacterium. The 16S rDNA nucleotide sequence homology of strain B5 with 2 strains of B. fusiformis reached 99.86%, so B5 was identified as B. fusiformis; (2) the algal-lysing effects of the algicidal bacterium B5 on M. aeruginosa, Chlorella and Scenedesmus were pronounced. The initial bacterial and algal cell densities strongly influence the removal rates of chlorophyll-a. The greater the initial bacterial cell density, the faster the degradation of chlorophyll-a. The greater the initial algal cell density, the slower the degradation of chlorophyll-a. When the bacterial cell density was 3.6 x 10(7) cells/ml, nearly 90% of chlorophyll-a was removed. When the chlorophyll-a concentration was less than 550 microg/L, about 70% was removed; (3) the strain B5 lysed algae by secreting metabolites and these metabolites could bear heat treatment.

The Algicidal Characteristics of One Algae-Lysing FDT5 Bacterium on Microcystis aeruginosa

One strain of algicidal bacterium which can inhibit Harmful algal blooms (HABs), FDT5, was isolated from activated sludge and found to have good algicidal effects on Microcystis aeruginosa. It was revealed that: The FDT5 was a Gram-negative bacterium and identified as Ochrobactrum sp.; The greater the initial bacterial cell density, the faster the degradation of chlorophyll a.; The algicidal efficiency was evaluated at the most favorable conditions which were a temperature of 30–35°C, a pH of 7.6 and complete darkness; The FDT5 strain lysed Microcystis aeruginosa not directly but by secreting metabolites which could withstand high temperatures and pressure.

Kinetic and mechanistic study of microcystin-LR degradation by nitrous acid under ultraviolet irradiation

Degradation of microcystin-LR (MC-LR) in the presence of nitrous acid (HNO(2)) under irradiation of 365nm ultraviolet (UV) was studied for the first time. The influence of initial conditions including pH value, NaNO(2) concentration, MC-LR concentration and UV intensity were studied. MC-LR was degraded in the presence of HNO(2); enhanced degradation of MC-LR was observed with 365nm UV irradiation, caused by the generation of hydroxyl radicals through the photolysis of HNO(2). The degradation processes of MC-LR could well fit the pseudo-first-order kinetics. Mass spectrometry was applied for identification of the byproducts and the analysis of degradation mechanisms. Major degradation pathways were proposed according to the results of LC-MS analysis. The degradation of MC-LR was initiated via three major pathways: attack of hydroxyl radicals on the conjugated carbon double bonds of Adda, attack of hydroxyl radicals on the benzene ring of Adda, and attack of nitrosonium ion on the benzene ring of Adda.

A SIMPLE, FAST, SOLVENT-FREE METHOD FOR THE DETERMINATION OF VOLATILE COMPOUNDS IN MAGNOLIA GRANDIFLORA LINN

Magnolia grandiflora Linn belonging to the Magnoliaceae family has been used to treat hypertension for many years in China. Based on microwave-assisted extraction (MAE) and headspace solid-phase microextraction (HS-SPME) followed by gas chromatography-mass spectrometry (GC-MS), the volatile compounds of Magnolia grandiflora L. were determined. Results indicated that the optimum conditions of the determination of the volatile compounds in Magnolia grandiflora L. were achieved with fiber coating of carboxen/polidimethylsiloxane, microwave power of 700 W and irradiation time of 4 min. Under the optimal conditions, for the first time, 48 volatile compounds were separated and identified from the fresh leaves of Magnolia grandiflora L. The highest content component of 48 compounds was γ-elemene (15.67%). Relative standard deviation (RSD) values less than 11% shows that the present method has good precision. The experimental results demonstrate that MAE-HS-SPME followed by GC-MS is a simple, time-saving solvent-free method, and it is a potential analytic tool for the determination of the volatile compounds in plant materials.

A Novel Photocatalytic Material for Removing Microcystin-LR under Visible Light Irradiation: Degradation Characteristics and Mechanisms

Background and Purpose Microcystin-LR (MC-LR), a common toxic species in contaminated aquatic systems, persists for long periods because of its cyclic structure. Ag3PO4 is an environment-friendly photocatalyst with relatively good degradation capacity for hazardous organic pollutants. This study aimed to investigate the degradation capacity of Ag3PO4 for MC-LR under visible light. Methods An Ag3PO4 photocatalyst was synthesized by the ion-exchange method and characterized by X-ray diffraction, field-emission scanning electron microscope, and UV-Vis spectrophotometer. MC-LR was quantified in each sample through high-performance liquid chromatograph. The degradation efficiency of MC-LR was affected by initial pH, initial Ag3PO4 concentration, initial MC-LR concentration, and recycle experiments. The degradation intermediates of MC-LR were examined by liquid chromatography-mass spectrometry (LC/MS). Results The degradation process can be well fitted with the pseudo-first-order kinetic model. The maximum MC-LR degradation rate of 99.98% can be obtained within 5 h under the following optimum conditions: pH of 5.01, Ag3PO4 concentration of 26.67 g/L, and MC-LR concentration of 9.06 mg/L. Nine intermediates were detected and analyzed by LC/MS. Three main degradation pathways were proposed based on the molecular weight of the intermediates and the reaction mechanism: (1) hydroxylation on the aromatic ring of Adda, (2) hydroxylation on the diene bonds of Adda, and (3) internal interactions on the cyclic structure of MC-LR. Conclusion Ag3PO4 is a highly efficient catalyst for MC-LR degradation in aqueous solutions.

Photodegradation of microcystin-LR catalyzed by metal phthalocyanines immobilized on TiO2-SiO2 under visible-light irradiation

Microcystins (MCs) are a group of monocyclic heptapeptide toxins produced by species of cyanobacteria. Since MCs exhibit acute and chronic effects on humans and wildlife by damaging the liver, they are of increasing concern worldwide. In this study, we investigated the ability of the phthalocyanine compound (ZnPc-TiO2-SiO2) to degrade microcystin-LR (MC-LR) in the presence of visible light. X-ray diffraction (XRD) and UV-Visible diffuse reflectance spectra (UV-Vis DRS) were utilized to characterize the crystalline phase and the absorption behavior of this catalyst. According to the results, XRD spectra of ZnPc-TiO2-SiO2 powders taken in the 2θ configuration exhibited the peaks characteristic of the anatase phase. UV-Vis DRS showed that the absorption band wavelength shifted to the visible range when ZnPc was supported on the surface of TiO2-SiO2. Subsequently, several parameters including catalyst dose, MC-LR concentrations and pH were investigated. The MC-LR was quantified in each sample through high-performance liquid chromatography (HPLC). The maximum MC-LR degradation rate of 80.2% can be obtained within 300 minutes under the following conditions: catalyst dose of 7.50 g/L, initial MC-LR concentration of 17.35 mg/L, pH 6.76 and the first cycling run of the photocatalytic reaction. Moreover, the degradation process fitted well with the pseudo-first-order kinetic model.

Mechanism and Reaction Pathways for Microcystin-LR Degradation through UV/H2O2 Treatment.

Microcystin-LR (MCLR) is the most common cyanotoxin in contaminated aquatic systems. MCLR inhibits protein phosphatases 1 and 2A, leading to liver damage and tumor formation. MCLR is relatively stable owing to its cyclic structures. The combined UV/H2O2 technology can degrade MCLR efficiently. The second-order rate constant of the reaction between MCLR and hydroxyl radical (·OH) is 2.79(±0.23)×1010 M−1 s−1 based on the competition kinetics model using nitrobenzene as reference compound. The probable degradation pathway was analyzed through liquid chromatography mass spectrometry. Results suggested that the major destruction pathways of MCLR were initiated by ·OH attack on the benzene ring and diene of the Adda side chain. The corresponding aldehyde or ketone peptide residues were formed through further oxidation. Another minor destruction pathway involved ·OH attack on the methoxy group of the Adda side chain, followed by complete removal of the methoxy group. The combined UV/H2O2 system is a promising technology for MCLR removal in contaminated aquatic systems.

Comprehensive risk assessment and source apportionment of heavy metal contamination in the surface sediment of the Yangtze River Anqing section, China

The Yangzi River has been seriously affected by intensive anthropogenic activities in recent years. In this study, the levels and distribution, risk assessment, and source apportionment of heavy metals in sediments were investigated in the Yangtze River (Anqing section). The heavy metal concentration and chemical characteristics (Cu/Pb/Zn/Cd/Cr/As/Hg) of 16 samples over four sections were measured using Atomic Fluorescence Spectrometry and Graphite Furnace Atomic Absorption Spectrometry. The metal concentration in the study area showed variance in different sampling sites. The mean heavy metal content was also higher than the background value. Vertical analysis of metal concentration showed the decreasing order from surface sediment. The analysis of Hakanson’s potential risk assessment indicated that the total potential ecological risk of these elements amounted to a considerable pollution level in the study area. The result of geo-accumulation index indicated that the risk of the studied metals had the following decreasing order: Cd > Hg > Pb > Cu > Zn > As > Cr. Based on the result of enrichment factor and principal component analysis, Cr, As, Hg, and partly Zn, Cu, and Cd mostly originated from natural sources. Pb and partly Cu and Zn mostly originated from gas companies, industries, and traffic sources, whereas Cd and partly Zn represented agricultural activities, such as fertilizer and pesticide consumption.

Transcriptional and Physiological Responses to Nutrient Loading on Toxin Formation and Photosynthesis in Microcystis Aeruginosa FACHB-905

An important goal of understanding harmful algae blooms is to determine how environmental factors affect the growth and toxin formation of toxin-producing species. In this study, we investigated the transcriptional responses of toxin formation gene (mcyB) and key photosynthesis genes (psaB, psbD and rbcL) of Microcystis aeruginosa FACHB-905 in different nutrient loading conditions using real-time reverse transcription quantitative polymerase chain reaction (RT-qPCR). Three physio-biochemical parameters (malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione (GSH)) were also evaluated to provide insight into the physiological responses of Microcystis cells. We observed an upregulation of mcyB gene in nutrient-deficient conditions, especially in nitrogen (N) limitation condition, and the transcript abundance declined after the nutrient were resupplied. Differently, high transcription levels were seen in phosphorus (P) deficient treatments for key photosynthesis genes throughout the culture period, while those in N-deficient cells varied with time, suggesting an adaptive regulation of Microsystis cells to nutrient stress. Increased contents of antioxidant enzymes (SOD and GSH) were seen in both N and P-deficient conditions, suggesting the presence of excess amount of free radical generation caused by nutrient stress. The amount of SOD and GSH continued to increase even after the nutrient was reintroduced and a strong correlation was seen between the MDA and enzyme activities, indicating the robust effort of rebalancing the redox system in Microcystis cells. Based on these transcriptional and physiological responses of M. aeruginosa to nutrient loading, these results could provide more insight into Microcystis blooms management and toxin formation regulation.

Performance of two ornamental plants for purifying eutrophication materials in urban riverway sewages

Experiments have been carried out to test the effect of two ornamental plants: Philodendron selloum (Ps) and Philodendron ‘Xanadan’ (PX) on removing nitrogen, phosphorus and organic contamination from urban riverway sewages. The results indicated that the effect is remarkable. The removal rate of TN (total nitrogen), TP (total phosphorous) and CODcr (chemical oxygen demand) were 27.41%, 61.40%, 12.44% (Ps) and 32.49%, 62.46%, 14.67% (PX) respectively in 30d. The average net removal rate of TN in first 5d was 73.3mg/(d·kg) and 56.24mg/ (d·kg) by Ps and PX, respectively, and it was up to 15.89mg/(d·kg) and 15.34mg/ (d·kg) for TP by two plants. The average net removal rate of CODcr in first 5d was 757.95mg/(d·kg) by Ps and 726.59mg/ (d·kg) by PX Two plants not only grew well, but also had high removal rate of eutrophication materials such as nitrogen and phosphorus. It is provided that planting PX and PS in urban riverway sewages is feasible to convert eutrophication materials into valuables and improve water quality.