Electrochemical determination of anaerobic microbial decay coefficients

The biokinetics of attached and suspended bacteria are an essential component of activated sludge models, anaerobic digestion models and biofilm models. These parameters are often assumed or “confirmed” based on the goodness-of-fit of the bioprocess models. Using a microbial fuel cell with a baffled reactor chamber, the attached- and mixed-growth microbial decay coefficients were evaluated under anaerobic conditions. The capability for real-time voltage recording allows easy and accurate measurement of the anaerobic microbial decay coefficients (b_L, lysis-regrowth approach), which were determined to be 0.11 ± 0.01 and 0.15 ± 0.01 d⁻¹ for attached (to anode) and mixed (present in the anode chamber) growth microorganisms, respectively. The corresponding half-saturation constants using glucose as a substrate were 204 ± 10 and 123 ± 1 mg COD l⁻¹. Hence, like an oxygen uptake rate-based approach to measure the microbial kinetics under aerobic conditions, the electrochemical recording provides an attractive method to measure anaerobic microbial decay coefficients.     

Types of Ectomycorrhiza as Pollution Stress Indicators: Case Studies in Slovenia

Mycorrhiza is the main spatial and temporal linkage between different constituents in a forest ecosystem. The functional compatibility and stress tolerance of ectomycorrhizal types is species specific, and therefore the information on the ectomycorrhizal community structure can add to the understanding of processes in forest ecosystems and can also be applied as tools for bioindication of pollution stress in forest soils. We have studied the effects of pollution (N and S) on trees and forest soils by: (1) quantification of ECM types diversity as in situ indicators in forest stands, (2) determination and quantification of pollution-sensitive or -insensitive ECM types as passive monitors, (3) root growth and development of ECM on nonmycorrhizal spruce seedlings, planted at the studied sites (active monitors), and (4) ECM infection (a bioassay based on mycorrhizal inoculum potential) of seedlings in an experimental set-up as ex situ testers. ECM species richness for Norway spruce trees (Picea abies) showed higher values in unpolluted sites than in polluted ones, while the differences were not significant for European beech trees (Fagus sylvatica). As pollution-sensitive or -insensitive ECM species in spruce forests, we suggest Hydnum rufescens (sensitive) and Paxillus involutus (unsensitive). Mycorrhizal potential in Norway spruce seedlings as a bioassay for soil N and S pollution was effective, and is suggested as an additional, standardized and widely comparable system in bioindication of soil pollution.     

细菌信息素研究进展

有关细胞信号的研究一直是生物学研究中的热点课题,尤其是动物细胞信号系统的研究已很深入,发现了许多信号分子和信号传导途径.但对微生物而言,长期以来的认识都是微生物,特别是细菌,一般只能被动地感受环境的变化,而没有群体的效应.其中唯一的特例是粘细菌(ｍｙｘｏｂａｃｔｅｒｉａ),在营养缺乏的条件下,通过释放ｃＡｍｐ等信号分子,促使营养细胞聚集,形成子实体和粘孢子[1].直至70年代,Ｈａｓｔｉｎｇ等通过对海洋发光细菌Ｖｉｂｒｉｏｆｉｓｃｈｅｒｉ和Ｖｉｂｒｉｏｈａｒｖｅｙｉ的发光机制的研究,发现发光细菌本身能产生一类小分子物…     

Characterization of the toxic effects of cadmium and 3.5-dichlorophenol on nitrifying activity and mortality in biologically activated sludge systems—effect of low temperature

Background, aims, and scope  Sometimes, urban wastewaters convey a more or less significant part of toxic products from industries or the craft industry. Nitrifying activity can be affected by these substances, implying higher ammonia concentrations in the outlet effluent and contributing to toxicity for the aquatic environment. Moreover, the more stringently treated wastewater standards now require a reliable treatment for nitrogen. One of the key issues is the identification of the inhibition behavior of nitrifying bacteria facing a toxic substance. This new understanding could then finally be integrated into models in order to represent and to optimize wastewater treatment plants (WWTP) operation in cases involving ‘toxic scenarios’. Materials and methods  The toxic substances studied in this work, cadmium and 3.5-dichlorophenol (3.5-DCP), are representative of chemical substances commonly found in municipal sewage and industrial effluents and symbolize two different contaminant groups. The effects of Cd and 3.5-DCP on nitrification kinetics have been investigated using respirometry techniques. Results  IC50 values determination gives concentrations of 3.1 mg/L for 3.5-DCP and 45.8 mg/L for Cd at 21 ± 1°C. The variation to low temperature seems to have no real effect on IC50 for DCP, but induces a decrease of cadmium IC50 to 27.5 mg/L at 14°C. Finally, specific respirometric tests have been carried out in order to determine the potential effect of these toxic substances on the nitrifying decay rate b _a . No significant effect has been noticed for Cd, whereas the presence of 3.5-DCP (at IC50 concentration) induced a dramatic increase of b _a at 20°C. The same behavior has been confirmed by experiments performed in winter periods with a sludge temperature around 12°C. Discussion  The target substances have different modes of action on activity and mortality, notably due to the abilities of the contaminant to be precipitated, accumulated, or even to be progressively degraded. Studies realized at low temperature confirmed this assumption, and put in evidence the effect of temperature on toxic substances capable of being biosorbed. However, the change in the sludge sample characteristics can be pointed out as a problem in the investigation of the temperature effect on nitrification inhibition, as biosorption, bioaccumulation, and predation are directly linked to the sludge characteristics (VSS concentration, temperature) and the plant operating conditions (loading rates, sludge age, etc.). Conclusions  This work brings new understandings concerning the action mode of these specific contaminants on nitrifying bacteria and, in particular, on the role of temperature. The experiments lead to the determination of the IC50 values for both toxic substances on biological nitrification. The inhibition mechanisms of Cd and 3.5-DCP on nitrifying activity have been simply represented by a non-competitive inhibition model. Recommendations and perspectives  Other experiments carried out in a continuous lab-scale pilot plant should be done with a proper control of the operating conditions and of the sludge characteristics in order to better understand the mechanisms of nitrification inhibition for each contaminant. Finally, these first results show that toxic substances can have an effect on the growth rate but also on the decay rate, depending on the characteristics of the toxic substance and the sludge. This eventual double effect would imply different strategies of WWTP operation according to the behavior of the contaminant on the bacteria.     

家用洗衣粉中磷对斜生栅藻生长的影响

以洗衣粉中的有机磷为磷源,通过室内模拟的方法研究在不同磷浓度的水体条件下斜生栅藻的生长情况,以及磷对斜生栅藻的生长是否有毒害作用.通过显微计数测定藻细胞数目来探讨洗衣粉中磷对斜生栅藻生长的影响;同时分析了洗衣粉中磷对斜生栅藻96 h生长期中光合色素的影响.结果表明,洗衣粉中的磷除了促进藻生长外,其浓度过低或过高都会抑制藻的生长.由实验结果可得,磷对藻生长的富营养化作用和毒性作用取决于磷浓度的高低.     

基于应力分析的机载电子设备可靠性加速增长试验技术研究

本文论述了基于应力分析的机载电子设备可靠性加速增长试验流程和方法,以某机载惯导产品为例说明了加速系数计算方法。这一方法对于其他机载电子产品的可靠性评估工作有一定的指导意义。     

细菌群落结构对水体富营养化的响应

于2005年2月在太湖不同营养水平湖区采集水样,寞接提取水样的总DNA,以细菌16SrDNA通用引物进行V3区PCR扩增,产物经DGGE(变性凝胶梯度电泳)分离后,获得水体细菌群落的16SrDNA指纹图谱;并运用FDC(表面荧光直接计数)方法对细菌丰度进行了测定.结果表明,水体中细菌的群落结构随着水体富营养化程度的改变产生明显变化,细菌数量呈现随水体营养水平增加而上升的趋势,营养水平较低的湖心区细菌数量仅为2.87×106 cells·mL-1,超富营养化的五里湖区水体中.细菌数量高达5.92×106cells·mL-1;细菌群落多样性随水体营养水平增加呈现显著的下降趋势,在超富营养化的1#、2#采样位点,细菌DGGE主要条带数量仅为23条,在沉水植物丰富区(贡湖湾)细菌DGGE主要条带数量达33条.PCA(主成分分析)的聚类结果表明,太湖水体中不同营养水平下的细菌群落多样性可大致归为3种类型,超富营养化的五里湖区水体细菌群落结构与梅粱湾及汞湖湾存在明显不同,可以大体归为超富营养类型、藻型湖区及草型湖区类型3种.此结果反映了水体富营养化过程中,由于营养物质的增加,促进了某些类群微生物的大量繁殖,水体中微生物的生物量显著增加;生态环境条件的恶化,造成了微生物多样性的下降,这可能导致原本稳定的水生态系统脆弱化.     

双壳类壳体时间序列的建立方法及存在的问题

利用双壳类壳体提取古气候古环境信息是生物碳酸盐研究的热点,而壳体定年一直是研究中的难点。相关研究主要观点是先找到一些时间控制点,再按照线性内插法来确定壳体的时间序列。本文综述了国内外目前双壳类壳体定年的常用方法,根据时间控制点的获得将这些方法归为以下几类:壳体日生长层法、壳体氧同位素法、数字图像技术法和微量元素法,介绍并讨论了每种方法的应用和存在的不足。研究者应该根据具体研究的生物和环境选择适合的方法。     

有机垃圾组分种群增长及修正一级产气动力学研究

以米饭、鸡蛋清、生菜、肥肉馅为原料,分别代表淀粉、蛋白质、纤维素、脂肪进行厌氧消化产沼气实验,并用种群增长模型和修正一级产气模型进行拟合.结果表明:脂肪的厌氧消化过程用修正Gompertz方程拟合效果较好,其余物料用Logistic方程拟合效果较好;脂肪的延滞期最长,为13 d,其次是蛋白质、纤维素,其值分别为8.72 d、6.24 d,淀粉的延滞期接近零.同时,建立了修正一级产气模型,并在延滞期之后用其模拟4种有机物厌氧消化产气过程,发现淀粉水解过程更趋向于遵循圆柱形颗粒模型,蛋白质、纤维素和脂肪水解过程更趋向于片状颗粒模型,淀粉和蛋白质的水解产气速度较快,脂肪稍慢,纤维素最慢;在延滞期内蛋白质和纤维素累积沼气产率都遵循零级水解动力学,脂肪的累积沼气产率遵循三次函数模型.在综合分析的基础上,得到了整个实验周期的产气动力学模型.     

颤蚓在活性污泥中的生长研究

以颤蚓为研究对象,活性污泥为底物,通过批量培养实验,考察了颤蚓在20℃和25℃2个不同温度下的生长状况.在16周的培养过程中,颤蚓在活性污泥中的生长较好地符合Logistic曲线;25℃更适于颤蚓生长,颤蚓个体在25℃下体重和体长的增长速率分别是0.0470mg·(条·d)-1和0.1936mm·(条·d)-1.同时,颤蚓在25℃下的体重-体长关系式为W=0.008 L2.028 (R2=0.8685),符合颤蚓科蠕虫体重-体长关系式的一般规律.与其它底物相比,以活性污泥为底物时的颤蚓生长并未表现出明显差别.