不同阴极对微生物燃料电池产电性能的影响比较

阴极催化性能及材料对微生物燃料电池(microbial fuel cells,MFCs)的产电特性及制造成本有很大影响。本研究选用金属铂(Pt)、活性炭作为催化剂、聚四氟乙烯(PTFE)和道康宁1-2577作为阴极的扩散层、碳布和不锈钢网作为阴极的基体材料制备得4种阴极,分别考察了相应MFC的产电性能和阴极特性。结果表明,采用传统Pt催化剂+PTFE扩散层+碳布制备成的阴极(Pt-PTC),MFC的最大输出电压为560 mV,最大功率密度为808 mW/m2,而采用活性炭+道康宁1-2577+不锈钢网制备成的阴极(AC-DCS),MFC的最大输出电压为510 mV,最大功率密度为726 mW/m2,两者的MFC产电性能极为接近。SEM结果表明,活性炭催化层表面和道康宁1-2577扩散层分别比Pt催化层及PTFE扩散层的更均匀光滑。阴极线性伏安测定结果表明,AC-DCS与Pt-PTC的电化学氧化性能较为接近。AC-DCS阴极成本仅为Pt-PTC的1/300左右,是一种低成本扩大化生产MFC阴极的新方法。     

铁氰化钾对双室微生物燃料电池曝气阴极性能的改善

为研究铁氰化钾对双室微生物燃料电池(MFC)阴极性能的改善效果,以碳毡和碳棒作为复合电极材料,乙酸钠为阳极电子供体,分别以氧气、铁氰化钾和氧气交替作为阴极电子受体.通过测定使用铁氰化钾作阴极电极液之前和之后的曝气阴极MFC的功率密度及极化曲线,比较曝气阴极MFC的内阻、开路电压(OCV)和最大输出功率的变化情况.实验结果表明,当以铁氰化钾作为MFC阴极电子受体时,MFC的内阻、开路电压和最大输出功率分别为24.2 Ω、744.2 mV和33.7 W/m3.曝气阴极MFC在采用铁氰化钾作电极液对阴极性能进行改善之前和改善之后的内阻由77.2 Ω降低到40.1Ω,OCV和最大输出功率分别由517.9 mV和2.1 W/m3提高到558.2 mV和4.4 W/m3.研究表明,铁氰化钾本身不仅具有优良的接受电子的能力,而且对电极材料(碳毡和碳棒)的电化学性能具有明显的改善作用,使得使用铁氰化钾之后的曝气阴极MFC的产电性能有了明显且持久性的提高.     

碳毡和碳布2种生物阴极材料微生物燃料电池产电性能

为了降低构建微生物燃料电池(MFCs)的成本,比较了以碳毡和碳布作为阴极材料,在阴极利用功能微生物作为催化剂时电池的产电性能。结果表明,两电池启动时间基本相同,20 d左右达到稳定,但稳定期碳布作阴极的电池电压比碳毡作阴极的电池电压高出了60 mV左右。碳毡和碳布作阴极时,电池在10 d和20 d的最大功率密度分别由10.24和11.14 mW/m2提升到了18.18和30.15 mW/m2,相应内阻则分别由1 000和600Ω降到了250和200Ω。循环伏安法(CV)显示两材料单独做电极时氧化还原情况相似,扫描电镜(SEM)观察到两者不同表面特性导致碳毡对污泥附着强于碳布,进而使氧气传递受到限制,产电降低。     

不同电极材料对阴极硝化耦合阳极反硝化微生物燃料电池性能的影响

为解决传统MFC反硝化菌在好氧阴极难以富集且脱氮效果差的问题,通过构建石墨MFC和碳刷MFC以阴极硝化耦合阳极反硝化的方式脱氮除碳,并对比分析2种不同电极MFC的性能。结果表明:在相同条件下石墨MFC的最大功率密度为6.71 W·m~(-3)NC,开路电压为902.13 mV;碳刷MFC的最大功率密度为5.11 W·m~(-3)NC,开路电压819.04 m V。启动阶段前15 d碳刷MFC的总氮去除率更高,之后石墨MFC的总氮去除率接近100%,碳刷MFC的总氮去除率在95%左右。石墨MFC的COD去除率高达93%,碳刷MFC的COD去除率在83%左右。相比于传统MFC,阴极硝化耦合阳极反硝化MFC不需要调节pH。相比于碳刷电极,石墨电极MFC可以启动和挂膜同时进行,缩短挂膜时间,且产电性能和脱氮除碳效果更好。     

温度、pH对微生物燃料电池产电的影响研究

采用SPSS分析软件,考察了双室微生物燃料电池(MFC)、单室MFC运行过程中,温度、pH与产电性能的相关关系。结果表明,碳纸双室MFC的日均电压与温度、阳极pH均未呈现显著相关关系,而与阴极pH呈极显著相关关系,产电的决定性因素为阴极反应;石墨毡/碳纸双室MFC日均电压与温度未呈现显著相关关系,而与阳极pH、阴极pH均呈极显著相关关系,产电的决定性因素为pH;单室MFC的产电性能受温度的影响较大,而pH对其影响不显著,对于单室MFC的运行调控应主要从温度入手。     

厌氧污泥和Geobacter sulfurreducens接种MFC的产电性能及其修复Cd污染土壤研究

利用混合菌种(厌氧污泥)和单一菌种(Geobacter sulfurreducens)以不同接种方式搭建单室土壤微生物燃料电池(MFC)反应器,考察不同MFC的产电性能及其对Cd污染土壤的修复效果。结果表明,将混合菌种集中接种于阳极碳毡表面的MFC1运行效果最佳,其在2d即可完成启动,输出电压稳定在0.225V左右,最大功率密度为35.00MW/m2,内阻为515.5Ω。土壤修复效果与MFC产电性能相关,MFC1产电性能最佳,因此土壤修复效果最好,稳定运行30d后阴极Cd富集率最高,达19.02%     

生物阴极微生物燃料电池中同步产电反硝化菌的分离鉴定与性能

利用反硝化筛选培养基从稳定运行的MFC-AA/O反应器阴极板上分离纯化反硝化细菌,经16S rRNA鉴定后,接种于双室MFC的阴极,测试其产电能力以筛选同步产电反硝化细菌,之后对MFC的运行温度和pH进行优化,最后通过扫描循环伏安曲线分析其产电机理。结果表明:分离获得的一株反硝化菌经鉴定为铜绿假单胞杆菌(Pseudomonas aeruginosa),该菌可实现同步产电脱氮,最高输出电压可达168 mV左右,其脱氮反应的最优pH为7.5,最适温度为30℃;在生物阴极起催化产电反硝化作用的可能是Pseudomonas aeruginosa的分泌物,其作为中介体,可从电极获得电子,完成硝酸盐的还原。上述结果说明,Pseudomonas aeruginosa作为接种MFC生物阴极的纯菌,可以实现同步产电反硝化,为反硝化生物阴极MFC的实际应用奠定基础。     

双室微生物燃料电池处理硝酸盐废水

基于双室微生物燃料电池(microbial fuel cell,MFC),针对阴极分别接种活性污泥(A-MFC)和反硝化细菌(D-MFC),研究其产电情况和硝酸盐废水去除效果。结果表明,在产电的同时都可有效去除废水中的硝酸盐污染物。在外接电阻100Ω的情况下,2种MFC均具有良好的产电性能,A-MFC和D-MFC达到的最大输出电压分别为119.6 mV和117.2mV,最大功率密度分别为23.40 mW/m2和26.63 mW/m2;同时两者在阴极室的平均反硝化速率分别为1.86 mg/(L.d)和2.19 mg/(L.d),阳极室的平均COD去除率分别为81.9%和82.4%。另外,通过扫描电镜观察可知,A-MFC和D-MFC阴极碳布表面形貌存在差异,并且阳极与阴极碳布表面形貌差异显著。     

微生物燃料电池处理含铜废水的研究

构建了以乙酸钠为阳极基质、Cu~(2+)为阴极电子受体的双室微生物燃料电池(MFC),考察了该MFC处理含铜废水的效果及Cu~(2+)浓度对MFC产电性能的影响。通过改变阴极液中CuSO_4的质量浓度(20~130mg/L),测试了MFC运行过程中的输出电压、输出功率密度、内阻、Cu去除率等指标。结果表明:Cu~(2+)可作为MFC的阴极电子受体;在外电路电阻为1 000Ω的条件下,Cu~(2+)质量浓度为130mg/L的MFC性能最佳,其稳定输出电压为0.33V、最大输出功率密度为114.42mW/m~2,内阻为231.62Ω,最高Cu去除率为84.59%;通过X射线衍射测试发现,阴极还原产物为Cu_2O。     

电子受体对微生物燃料电池产电性能的影响

以厌氧污泥为接种菌源,醋酸钠为阳极基质,分别构建了铁氰化钾和过硫酸铵为电子受体的双室微生物燃料电池(MFC),并研究了MFC在不同电子受体下的产电性能。结果表明,以铁氰化钾和过硫酸铵为电子受体的MFC最大稳定输出电压均随着电子受体浓度的升高而增大。当铁氰化钾质量浓度大于2.0g/L时,MFC最大稳定输出电压增幅不大。两种MFC的内阻均随电子受体浓度的增大而降低。阴、阳极溶液体积相等,外阻为5 000Ω时,以10.0g/L过硫酸铵为电子受体,MFC最大开路电压和最大输出功率密度分别为1 029.0mV和385mW/m3;以10.0g/L铁氰化钾作为电子受体,MFC最大开路电压和最大输出功率密度分别为711.8mV和73mW/m3,均小于以过硫酸铵为电子受体的最大开路电压和最大输出功率密度。因此,过硫酸铵是一种理想的电子受体,能够提高MFC产电性能。     

Fire as a Soil-Forming Factor

In the span of a human generation, fire can, in theory, impact all the land covered by vegetation. Its occurrence has many important direct and indirect effects on soil, some of which are long-lasting or even permanent. As a consequence, fire must be considered a soil-forming factor, on par with the others traditionally recognized, namely: parent material, topography, time, climate, living beings not endowed with the power of reason, and humans.     

Perchlorate as an environmental contaminant

Perchlorate anion (ClO4-) has been found in drinking water supplies throughout the southwestern United States. It is primarily associated with releases of ammonium perchlorate by defense contractors, military operations, and aerospace programs. Ammonium perchlorate is used as a solid oxidant in missile and rocket propulsion systems. Traces of perchlorate are found in Chile saltpeter, but the use of such fertilizer has not been associated with large scale contamination. Although it is a strong oxidant, perchlorate anion is very persistent in the environment due to the high activation energy associated with its reduction. At high enough concentrations, perchlorate can affect thyroid gland functions, where it is mistakenly taken up in place of iodide. A safe daily exposure has not yet been set, but is expected to be released in 2002. Perchlorate is measured in environmental samples primarily by ion chromatography. It can be removed by anion exchange or membrane filtration. It is destroyed by some biological and chemical processes. The environmental occurrence, toxicity, analytical chemistry, and remediative approaches are discussed.     

Acetochlor as a soil pollutant

Acetochlor is a widely used herbicide all over the world. Similarly to other organic pollutants, the environmental fate of the acetochlor is strongly related to its adsorption properties. Static adsorption equilibrium measurements were carried out at 25 degrees C on different types of Hungarian soils characterized by varying amounts of organic matter and pH values. Isotherms obtained under different conditions, as well as on various soils, exhibit a similar shape, thus indicating a two-step adsorption process. The plots cannot be interpreted according to the classes of isotherms suggested by Giles. The adsorption coefficients (K) were estimated from the initial slope of the curves. These values were determined not only by the type of the soil, but also by the composition of the aqueous media. The organic matter adsorption coefficients (Kom) were also calculated and they were approximately identical for soils of high organic matter. Due to the low value of the adsorption coefficients, the acetochlor is a rather mobile pollutant of the soil posing a potential danger to the aquatic environment. For soils with high organic content, the Kom values are similar to each other and, due to the significant coverage of the inorganic surfaces, the adsorption is controlled by the solute-organic substance interactions. The adsorption of weakly polar compounds, however, is remarkable even on those soils where the organic content is low. In this case, the binding is governed by the solute-inorganic surface interactions. This conclusion is nicely proved by the adsorption of the acetochlor on quartz. According to our hypothesis, the second part of the adsorption step is controlled by the solute-adsorbed solute interactions. The role of the organic matter in this region of the isotherm is probably negligible. As the organic matter content of the soils plays an important role in the acetochlor adsorption, humic substances must have a strong influence upon the transport of this compound. Experiments to obtain adsorption isotherms of further pesticides and the development of a quantitative model are in progress.     

Spider webs as environmental indicators

Analysis of spider webs from limestone arches in New South Wales, Australia showed levels of lead and zinc to be several times higher at Jenolan Caves than reference sites at Abercrombie and Wombeyan Caves. The high concentrations at Jenolan were attributed to emissions from motor vehicles that travel through the arch. Analysis of water-soluble ions in webs from Jenolan and Abercrombie Caves showed large differences between the sites, which could be explained by differences in the geology and biology of the cave environments. Spider webs proved useful indicators of environmental chemistry and undoubtedly have applications beyond the cave environments studied here.     

Microbial phytotoxins as potential herbicides

Abstract

Microbes are sources of a diverse array of phytotoxic compounds. These compounds are generally structurally different from commercial herbicides, targeting different molecular sites of action within the plant. These novel structures and sites can be excellent leads for the discovery and development of safer synthetic herbicides. Microbial phytotoxins are often more environmentally benign than synthetic herbicides. Examples of phytotoxins from fungi (AAL‐toxin, cornexistin, cyperin, and tentoxin) with novel structures and sites of action are discussed. AAL‐toxin is toxic to a wide variety of weeds at very low dose rates. AAL‐toxin and many of its analogues kill plants by inhibiting a ceramide synthase‐like enzyme, causing rapid accumulation of free sphingoid bases that disrupt membranes. Cornexistin appears to be metabolically cnverted to an inhibitor of certain aspartate amino transferase isoenzymes. Its activity can be reversed by feeding aspartate and glutamate or with tricarboxylic acid cycle intermediates. Its activity is much like that of (aminooxy)acetate. Cyperin is a diphenylether phytotoxin that inhibits protoporphyrinogen oxidase, but does not kill plants by this mechanism. It appears to have other effects on porphyrin metabolism. Tentoxin is toxic by two mechanisms. It disrupts chloroplast development by inhibiting the processing of a nuclear‐coded plastid protein, and it also inhibits photophosphorylation by acting as an energy transfer inhibitor of coupling factor 1 ATPase. Other examples of phytotoxins from microbes with promise as herbicides will be mentioned.     

Ozone as a Tobacco Toxicant

Ozone is very toxic to tobacco, causing serious injury in greenhouses and fields. Certain varieties, differing in sensitivity, have proved useful as indicators of the presence, and to some extent the level, of air-polluting ozone. Environmental factors alter plant response to ozone and must be taken into account. What is now recognized as typical ozone injury to tobacco was first observed in Connecticut in 1951, Maryland in 1952, eastern North Carolina in 1953, and Ontario, Canada, in 1955. Cracking of rubber strips exposed daily at six locations in 1959 in the Connecticut Valley showed ozone concentrations were highest the day before a fleck outbreak, resulting in more than a million dollar loss. Measurement with a Mast ozone recorder from July to mid-October for two seasons at Beltsville, Md., six miles northeast of the District of Columbia, indicated 2.5 pphm as the average daily maximum value, 5 pphm as the level when plant injury is expected, and 10 pphm as very high and infrequent. The neutral buffered Kl method indicated higher ozone values, but about 15 pphm was maximum with this method. Shading portions of leaves for three hours in midday prevented ozone injury. Increased injury in the different tobacco areas was related to increased culture of more susceptible varieties. Although various antiozonants applied to the leaf, or even applied to cloth shade, reduce damage, the development of resistant tobaccos has proved the better means of control. Premature senescence and related chlorosis as well as fleck were prevented by carbon-filtered air, indicating that ozone may be a more important toxicant than previously recognized. Possibly oxidants other than ozone contributed to plant injury, but, if present, they were removed by carbon-filters. Growth of an ozone-sensitive tobacco Bel-W3, as indicated by dry weight, was only half as much in ambient as in carbonfiltered air in one experiment with chambers continued for 5 weeks. Evidence of synergistic action of sulfur dioxide and ozone is reported. Subthreshold concentrations of these toxicants produced injury following exposure of tobacco to mixed gases, whereas no injury resulted from the same concentration of the individual gases.     

Immobilized humic substances as sorbents

A new method was developed for the immobilization of humic substances. Humic acids (HA) immobilized onto different carriers were studied as sorbents for organic and inorganic substances. The sorption isotherms of 4-aminoazobenzene, Crystal Violet, Methylene Green, and flavine mononucleotide on immobilized HA show that pH and salt concentration have a significant effect on the sorption process, largely depending on the properties of polymeric matrix. Humic acids from different sources showed differing sorption capacity for the studied groups of substances.     

植物作为反硝化碳源

研究得到一种新型的筛选反硝化碳源的方法:可以通过比较材料浸出液的C/N值,筛选出有效的反硝化碳源;对芦苇秸秆、梧桐黄叶、梧桐绿叶、橘树叶、玉米秸秆和玉米芯6种材料浸出液的C/N值进行了研究,其中当以叶片作为反硝化固相碳源时,应该选取新鲜叶片作为研究对象。橘树叶和玉米芯均属于良好的反硝化碳源。以驯化后的河泥作为反硝化污泥,可以利用橘树叶或者玉米芯作为反硝化固相碳源,进行持续脱氮除磷反应,其中橘树叶脱氮效果强于玉米芯,而玉米芯除磷能力强于橘树叶。扫描电镜实验表明,橘树叶和玉米芯均适合作为生物膜载体。     

The suitability of gastropods as biomarkers

The measurement and induction of mixed function oxyigenases (MFOs) of limnetic gastropods were investigated to estimate their suitability as biomarkers. A determination of MFO activities was performed through the measurement of ethoxyresorufin-O-dealkylase (EROD), pentoxy-(PROD) and benzoxyresorufin-O-dealkylase-activity (BROD). Optimal measuring conditions of these activities were investigated in preparations of the digestive gland of 4 species of limnetic gastropods. Results indicate that MFO-activity inhibiting substances are accumulating in the microsomal pellet, the fraction commonly used for the measurement of MFO-activities. Therefore, the fraction used for induction studies was the postmitochondrial supernatant (PMS). EROD, PROD, and BROD activity ofPlanorbis planorbis andPlanorbis carinatus were measured after a treatment with Aroclor 1254 for 1–17 days. Maximal induction of EROD and PROD were 6 and 10 times the value in the control group ofP. carinatus, respectively induction inP. planorbis was lower. BROD-activity could not been measured inP. planorbis. InP. carinatus, BROD-activity increased to a maximum of 2 times after traetment with Aroclor 1254. The level of induction of EROD-activity is comparable to results described in analog studies with fish.     

Horizon scanning for South African biodiversity: A need for social engagement as well as science

Ambio - A horizon scan was conducted to identify emerging and intensifying issues for biodiversity conservation in South Africa over the next 5–10 years. South African biodiversity...