Phenotypic plasticity in Scenedesmus incrassatulus (Chlorophyceae) in response to heavy metals stress

The microalgae genus Scenedesmus is commonly found in freshwater bodies, wastewater facilities and water polluted with heavy metals. Phenotypic plasticity in Scenedesmus has been documented in response to a wide variety of conditions; however, heavy metals have not been comprehensively documented as phenotypic plasticity inducers. In this study, we report the phenotypic plasticity of Scenedesmus incrassatulus (a non-spiny, four-cell coenobium forming species) in response to EC₅₀ value of copper, cadmium and hexavalent chromium. S. incrassatulus was grown in batch cultures in the presence of each metal. Chlorophyll-a content, cell size, parameters derived from the schematic energy-flux model for photosystem II, and morphotype expressions were recorded. Divalent cation metals induced unicellular forms, and hexavalent chromium produced out-of-shape coenobia corresponding to various stages of autospore formation. The changes induced by divalent metals were interpreted as phenotypic plasticity, because they were always associated to population doublings and were reversible when toxicant pressure was removed (only for Cu). Copper was the best inductor of unicellular forms and also affected significantly all the photosynthetic parameters measured. The developed morphotypes could confer ecological advantages to S. incrassatulus in metal stressed environments.     

Copper complexing properties of dissolved organic materials exuded by the freshwater microalgae Scenedesmus acuminatus (Chlorophyceae)

Dissolved organic materials released by the freshwater microalgae Scenedesmus acuminatus were fractionated into low- and high-molecular weight materials, which were investigated for their capacity to bind copper. The high-molecular weight material was also investigated for its monosaccharide composition and is further discussed in relation to the copper binding property. S. acuminatus was grown in batch cultures under laboratory controlled conditions and harvested at the beginning of stationary growth phase when exuded organic materials were obtained. Copper-complexing property of the total exuded organic materials and exopolysaccharides before and after freeze-drying was evaluated by complexometric titrations and Scatchard Plot Analysis of the titration data. The results revealed the presence of two copper-complexing ligands in the total exuded material, but only one in the exopolysaccharide. Stronger copper-complexing ligands are associated to low molecular weight compounds (LogK'1=7.3, LogCL1=-5.6; LogK'2=6.3, LogCL2=-5.1), whereas weaker ligands to the high molecular weight fraction (LogK'2=6.4, LogCL2=-5.6). Although freeze-drying the polymeric organic material (exopolysaccharide) may result in conformational changes of the molecule, no effect on copper-complexing properties was detected. Gas chromatography was used to evaluate the monosaccharide composition of the microalgal exopolysaccharide, which detected high content of mannose and 12% of acid monosaccharides.     

Growth, photosynthetic and respiratory responses to sub-lethal copper concentrations in Scenedesmus incrassatulus (Chlorophyceae)

In the present paper we investigated the effects of sub-lethal concentrations of Cu²⁺ in the growth and metabolism of Scenedesmus incrassatulus. We found that the effect of Cu²⁺ on growth, photosynthetic pigments (chlorophylls and carotenoids) and metabolism do not follow the same pattern. Photosynthesis was more sensitive than respiration. The analysis of chlorophyll a fluorescence transient shows that the effect of sub-lethal Cu²⁺ concentration in vivo, causes a reduction of the active PSII reaction centers and the primary charge separation, decreasing the quantum yield of PSII, the electron transport rate and the photosynthetic O₂ evolution. The order of sensitivity found was: Growth > photosynthetic pigments content = photosynthetic O₂ evolution > photosynthetic electron transport > respiration. The uncoupled relationship between growth and metabolism is discussed.     

Photodegradation of hexabromocyclododecane (HBCD) by Fe(III) complexes/H2O2 under simulated sunlight

Hexabromocyclododecane (HBCD) is a globally produced brominated flame retardant used primarily as an additive flame retardant in polystyrene and textile products. Photodegradation of HBCD in the presence of Fe(III)-carboxylate complexes/H₂O₂ was investigated under simulated sunlight. The degradation of HBCD decreased with increasing pH in the Fe(III)-oxalate solutions. In contrast, the optimum pH was 5.0 for the Fe(III)-citrate-catalyzed photodegradation within the range of 3.0 to 7.0. For both Fe(III)-oxalate and Fe(III)-citrate complexes, the increase of carboxylate concentrations facilitated the photodegradation. The photochemical removal of HBCD was related to the photoreactivity and speciation distribution of Fe(III) complexes. The addition of H₂O₂ markedly accelerated the degradation of HBCD in the presence of Fe(III)-citrate complexes. The quenching experiments showed that ·OH was responsible for the photodegradation of HBCD in the Fe(III)-carboxylate complexes/H₂O₂ solutions. The results suggest that Fe(III) complexes/H₂O₂ catalysis is a potential method for the removal of HBCD in the aqueous solutions.     

UV/H2O2/Fe-FeOxH2x-3和UV/H2O2工艺降解水中富里酸的研究

采用硼氢化钠还原法制备核-壳结构的Fe-FeOxH2x-3复合材料,研究了富里酸在UV/H2O2和UV/H2O2/Fe-FeOxH2x-3两种不同反应体系下的降解情况。结果表明,核-壳结构Fe-FeOxH2x-3的存在,提高了UV/H2O2降解富里酸的反应速率,TOC去除达到84%。采用XAD树脂吸附法对反应前后的富里酸进行化学分级表征,结果表明,富里酸经反应后憎水酸（HoA）、弱憎水酸（WHoA）和憎水中性物质（HoN）都有所减少,进而转化为亲水性物质（HiM）;用超滤膜法对富里酸进行物理分级表征,考察了富里酸在反应前后分子量分布的变化情况。同时,富里酸经过反应后生成的中间产物降低了三氯甲烷生成趋势。     

H2O2溶液同时脱硫脱硝实验研究

二氧化硫和氮氧化物是电厂产生的主要大气污染物,研究焦点越来越集中在在一个反应器内实现同时脱硫脱硝。实验以H2O溶液作为吸收液,在自制的鼓泡反应器内,对模拟烟气进行同时脱硫脱硝的实验研究,实验结果表明：H2O浓度、反应温度、NO浓度、SO2浓度、烟气流量对脱除率影响显著,pH、氧含量对脱硝率影响不大。在整个实验范围内脱硫效率总是保持在98．5％以上,脱硝效率最高达到67．4％。     

Hydroxyl (OH) radical production rates in snowpacks from photolysis of hydrogen peroxide (H2O2) and nitrate (NO3−)

Atmospheric chemistry directly above snowpacks is strongly influenced by ultraviolet (UV) radiation initiated emissions of chemicals from the snowpack. The emission of gases from the snowpack to the atmosphere is in part due to chemical reactions between hydroxyl radical, OH (produced from photolysis of hydrogen peroxide (H₂O₂) or nitrate (NO₃⁻)) and impurities in the snowpack. The work presented here is a radiative-transfer modelling study to calculate the depth-integrated production rates of hydroxyl radical from the photolysis of hydrogen peroxide and nitrate anion in snow for four different snowpacks and for solar zenith angles 30°–90°. This work also demonstrates the importance of hydrogen peroxide photolysis to produce hydroxyl radical relative to nitrate photolysis with (a) different snowpacks, (b) different ozone column depths, and (c) snowpack depths. The importance of hydrogen peroxide photolysis over nitrate photolysis for hydroxyl radical production increases with increasing depth in snowpack, column ozone depth, and solar zenith angle. With a solar zenith angle of 60° the production of hydroxyl radical from hydrogen peroxide photolysis accounts for 91–99% of all hydroxyl radical production from hydrogen peroxide and nitrate photolysis.     

Absorption cross-sections of atmospheric constituents: NO2, O2, and H2O

Absorption spectroscopy, which is widely used for concentration measurements of tropospheric and stratospheric compounds, requires precise values of the absorption cross-sections of the measured species. NO₂, O₂ and its collision-induced absorption spectrum, and H₂O absorption cross-sections have been measured at temperature and pressure conditions prevailing in the Earth’s atmosphere. Corrections to the generally accepted analysis procedures used to resolve the convolution problem are also proposed.     

Seasonal evolutions of ozone (O3) and its nitrogen precursors (NO, NO2) in urban Sfax (Tunisia)

Seasonal evolution of ozone (O3) and its nitrogen precursors (NO, NO2) in downtown Sfax (Tunisia) was monitored. Nitrogen oxides are shown to be closely related to local vehicle sources. Seasonal ozone levels, however, are shown to be dependent on regional meteorological conditions. High ozone levels are due to the effect of anticyclones and stratosphere intrusions (cut-off lows). Low levels are associated with cyclonic conditions of small vertical range of motion. Other than these particular conditions, ozone levels are shown to be relatively higher in fall and winter seasons, characterised by a very steady atmosphere. Overall, the examined meteorological conditions, the ozone concentrations observed in downtown Sfax are characterised by clear day/night cycles, which can be explained by the significant ventilation of the region.     

H2O2/Fe0、H2O2/Fe2+、H2O2/Fe3+3种体系处理印染废水

采用H2O2/Fe0、H2O2/Fe2+、H2O2/Fe3+3种体系分别对印染废水进行处理,研究pH 值、H2O2投加量、不同价态铁元素的投加量及反应时间对印染废水的COD和色度处理效果的影响。实验最佳的处理条件:H2O2/Fe0体系在pH 为3.0,Fe0投加量为3.0 mmol/L,H2O2投加量为9.0 mL/L,反应时间为40 min时,COD去除率达到95.99%,色度去除率达到100%;H2O2/Fe3+体系在pH 为3.0,Fe3+投加量为5.0 mmol/L,H2O2投加量为12.5 mL/L,反应时间为100 min时,COD去除率达到95.89%,色度去除率达到100%;H2O2/Fe2+体系在pH 为3.0,Fe2+投加量为6.0 mmol/L,H2O2投加量为12.0 mL/L,反应时间为100 min时,COD去除率达到95.85%,色度去除率达到100%。对比分析3种体系在各因素下的处理结果,H2O2/Fe0体系和H2O2/Fe3+体系都要优于H2O2/Fe2+体系,其中H2O2/Fe0体系的处理效果最好。     

Influence of various reaction parameters on 2,4-D removal in photo/ferrioxalate/H(2)O(2) process

The influence of various reaction parameters on herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) removal were examined in the photo/ferrioxalate/H(2)O(2) system, with regard to: (1) sulfate, phosphate, and z.rad;OH scavenger, as solution constituent; and (2) light intensity, ferrioxalate, H(2)O(2), and oxalate concentration, as operating parameter. In terms of 2,4-D removal, the photo/ferrioxalate/H(2)O(2) system has always been superior to the photo/Ferric ion/H(2)O(2) system, despite the high presence of anions (sulfate 100 mM, phosphate 1 mM) or z.rad;OH scavenger. Not only the rate of 2,4-D removal, but also the decomposition rate of H(2)O(2) and oxalate proportionally increase with light intensity. The ferrioxalate concentration determines the light absorption fraction, and thus, controls the rates of 2,4-D removal, and the decomposition of H(2)O(2) and oxalate, are predicted from kinetic formulations. The optimal concentration of H(2)O(2) and oxalate, according to the extent of the z.rad;OH scavenging reaction with these reagents, has been demonstrated for 2,4-D removal. It was found that an increasing oxalate concentration, which bears the burden of increased dissolved organic carbon (DOC), does not occur. This is because its decomposition, as a result of the photochemical reduction of the ferric oxalate complex, results in a decrease of the equivalent DOC. The importance of the key reaction factors to be considered, when applying this system to real wastewater treatment, is also discussed.     

Quantitative structure-activity relationships of nitroaromatics toxicity to the algae (Scenedesmus obliguus)

The DFT-B3LYP method, with the basis set 6-311G( * *), was employed to calculate the molecular geometries and electronic structures of 25 nitroaromatics. The acute toxicity (-lgEC(50)) of these compounds to the algae (Scenedesmus obliguus) along with hydrophobicity described by logK(OW), and two quantum chemical parameters-energy of the lowest unoccupied molecular orbital, E(LUMO), and the charge of the nitro group, [ForQ(NO2), were used to establish the quantitative structure-activity relationships (QSARs). For 18 mononitro derivatives, the hydrophobicity parameter logK(OW) could interpret the toxic mechanism successfully. Dinitro aromatic compounds were susceptible to be reduced to aniline for their electrophilic nature. Their toxicity was controlled mainly by electronic factors instead of hydrophobicity. The electronic parameters, E(LUMO) and Q(NO2), were used to yield the following model: -lg EC(50) = 3.746 - 25.053 E(LUMO) + 6.481 Q(NO2) (n=22, R=0.926, SE=0.206, F=56.854, P<0.001). The predicted toxic values using the above equation are in good agreement with the experimental values.     

O3/H2O2法去除浮选药剂丁基黄药

采用O3/H2O2法去除水中丁基黄药,考察了H2O2/O3摩尔比、pH值、丁基黄药初始浓度、温度和自由基抑制剂对丁基黄药的去除效果的影响。结果表明,在相同O3投加量下,H2O2量越大,丁基黄药去除率越高。pH值为7～9,温度在293～303 K的范围内,O3/H2O2对丁基黄药都有很高的去除率。碳酸氢根和叔丁醇能在一定程度上降低丁基黄药的降解效率。研究还发现,在O3和H2O2投加量相同的条件下,H2O2多次投加对水中丁基黄药的处理效果明显优于一次性投加。GC/MS分析表明,O3/H2O2氧化丁基黄药氧化产物为羧酸类物质。     

UV/H2O2工艺降解环丙沙星的研究

采用UV/H2O2工艺去除水体中的喹诺酮类抗生素环丙沙星（CIP）。考察了溶液pH值、H2O2投加量以及水体基质对环丙沙星降解效率的影响,分析了降解产物的生成情况。研究表明,环丙沙星的降解符合拟一级反应动力学模型。降解速率受溶液pH值的影响,酸性及中性条件,有利于环丙沙星的降解。H2O2投加量的增大,使得降解速率逐渐增大,但速率增幅逐渐变缓;最佳H2O2/环丙沙星摩尔比为2 000。实际水体中存在的NOM、NO3-,促进了单独UV作用下,环丙沙星的降解。水体中的.OH焠灭剂,抑制了UV/H2O2联合作用下,环丙沙星的降解;实际水体中的光解速率常数低于超纯水中的光解速率常数。GC-MS分析表明,UV/H2O2工艺,使环丙沙星氧化降解生成氨基乙酸、丙二酸、丙三醇和对苯二甲酸等小分子有机物。     

臭氧/双氧水/紫外光联用降解饮用水中溴氯乙腈的试验研究

为减少饮用水氯化消毒过程中产生的含氮消毒副产物溴氯乙腈(BCAN),降低其潜在的致癌风险,分别采用臭氧(O3)、双氧水(H2O2)和紫外光(UV)及其联合工艺,考察了不同试验条件下BCAN的降解效果及影响因素,并探讨了其降解机制和动力学规律。结果表明,O3、H2O2和UV工艺对BCAN降解效果都不理想,UV/H2O2和UV/H2O2/O3联合工艺可以较有效地降解水中的BCAN。在BCAN初始质量浓度为20μg/L、紫外光强为31μW/cm2、H2O2质量浓度为40 mg/L、O3质量浓度为7.9mg/L条件下,反应进行120min后,UV/H2O2联合工艺与UV/H2O2/O3联合工艺对BCAN的降解率分别为77.50%、94.05%。UV/H2O2/O3联合工艺对BCAN的降解效果比UV/H2O2联合工艺更好,UV/H2O2和UV/H2O2/O3联合工艺降解BCAN均符合一级反应动力学规律。     

UV/草酸铁/H2O2法处理乙草胺废水的研究

对UV/草酸铁/H2O2法处理乙草胺废水进行研究,考察了H2O2浓度、FeSO4浓度、K2C2O4浓度、pH值及反应时间对乙草胺去除效果的影响.结果表明,当H2O2/FeSO4/K2C2O4(化学剂量数比)=5051,H2O2/乙草胺初始COD(质量浓度比)=31时,该技术对乙草胺的去除率可达85%以上.这表明,采用UV/草酸铁/H2O2法可以有效地处理含乙草胺废水.     

O3/H2O2降解阿特拉津影响因素研究

采用O3/H2O2氧化去除水中内分泌干扰物阿特拉津,考察了反应条件及水质对去除的影响,并对反应机制进行了初步探讨。阿特拉津初始浓度2 mg/L,投量为7.5 mg/L的O3单独氧化去除率为27.2%;相同O3投量下,控制H2O2/O3摩尔比为0.75,5 min阿特拉津的去除率最高可达96.5%;pH 值为7.5～8.5,温度在25～40℃的范围内,都维持了较高的去除率,表明H2O2/O3体系对阿特拉津的去除效果良好,降解速度快,反应条件温和。0.5 mg/L的腐殖酸,对阿特拉津的去除影响不大,腐殖酸浓度为1、2和5 mg/L时,平均去除率分别为63.4%、50.7%和30.2%;碳酸氢钠的浓度为50和200 mg/L时,去除率分别为88.1%和73.8%,说明水质对阿特拉津的去除影响较大。叔丁醇的浓度为5和20 mg/L时,阿特拉津的去除率分别降低到44.7%和27.5%,去除率随自由基抑制剂叔丁醇增加而降低,说明H2O2/O3降解阿特拉津主要为该体系产生的羟基自由基的贡献。     

Photooxidation of naphthalenesulfonic acids: comparison between processes based on O(3), O(3)/activated carbon and UV/H(2)O(2)

The aim of the present study was to analyze and compare the efficacy of UV photodegradation with that of different advanced oxidation processes (O(3), UV/H(2)O(2), O(3)/activated carbon) in the degradation of naphthalenesulfonic acids from aqueous solution and to investigate the kinetics and the mechanism involved in these processes. Results obtained showed that photodegradation with UV radiation (254 nm) of 1-naphthalenesulfonic, 1,5-naphthalendisulfonic and 1,3,6-naphthalentrisulfonic acids is not effective. Presence of duroquinone and 4-carboxybenzophenone during UV irradiation (308-410 nm) of the naphthalenesulfonic acids increased the photodegradation rate. Addition of H(2)O(2) during irradiation of naphthalenesulfonic acids accelerated their elimination, due to the generation of ()OH radicals in the medium. Comparison between UV photodegradation 254 m and the advanced oxidation processes (O(3), O(3)/activated carbon and UV/H(2)O(2)) showed the low-efficacy of the former in the degradation of these compounds from aqueous medium. Thus, among the systems studied, those based on the use of UV/H(2)O(2) and O(3)/activated carbon were the most effective in the oxidation of these contaminants from the medium. This is because of the high-reactivity of naphthalenesulfonic acids with the *OH radicals generated by these two systems. This was confirmed by the values of the reaction rate constant of *OH radicals with these compounds k(OH), obtained by competitive kinetics (5.7 x 10(9) M(-1) s(-1), 5.2 x 10(9) M(-1) s(-1) and 3.7 x 10(9) M(-1) s(-1) for NS, NDS and NTS, respectively).     

超声和H2O2对双酚A模拟废水的毒性源头消减

对含双酚A模拟废水处理的序列间歇式活性污泥法(SBR)活性污泥系统,进行分别以超声破碎和投加H2O2氧化两种模式的污泥源头处理。分别以发光菌表征的微生物毒性和种子发芽率表征的植物毒性来衡量污泥毒性,通过对照污泥经源头处理前后的水相指标变化和以酶活性表征的污泥特性变化,考察污泥源头处理模式对污泥毒性消减效果和对污泥特性的影响。结果表明,污泥经源头处理后超声组污泥毒性最大,而H2O2组污泥毒性最小,空白组污泥毒性居中。种子发芽率表征的植物毒性与发光菌表征的微生物毒性成正相关关系。污泥经超声和H2O2源头处理后的脱氢酶活性和过氧化氢酶活性的变化趋势与污泥毒性显著相关。     

UV/H2O2/草酸铁络合物光降解邻苯二甲酸二丁酯研究

研究了邻苯二甲酸二丁酯(DBP)在UV/H2O2/草酸铁络合物体系中的光降解.结果表明,UV/H2O2/草酸铁络合物能有效地光解DBP;在pH值为4时,DBP光解速率最快,中性和碱性条件下光解效率降低;DBP的光解速率随H2O2浓度的升高而增大,但H2O2浓度较大时,其对·OH的清除作用使DBP的光解速率减慢;[Fe3 ]/[C2O42]＜1/10,DBP光解速率随Fe3 浓度增大明显提高,[Fe3 ]/[C2O42]＞1/10时,引起DBP光解速率的增加不明显.