城市雨水问题与可持续发展对策

城市化的快速发展带来了一系列的雨水问题,如雨水径流污染、水资源严重短缺、洪灾风险加大等,雨水是城市可持续发展的关键问题之一。通过对近年来北京城区雨水水质与水量的监测和分析,根据城市可持续发展的总体要求,提出了解决城市雨水问题的指导思想和对策。     

煤矿人为失误的原因及控制

随着科学技术的进步,机器设备的可靠性得到了大幅度的提高,人为失误导致的事故比例快速上升.掌握人为失误的原因,进而控制人为失误的发生是有效减少事故发生的重要措施.在对神火煤电股份有限公司新庄矿深入调查了解的基础上,初步探讨了煤矿人为失误的原因,提出了控制人为失误的有效途径.     

Ecological selection of bacterial taxa with larger genome sizes in response to polycyclic aromatic hydrocarbons stress

Polycyclic aromatic hydrocarbons(PAHs) are ubiquitous priority pollutants that cause great damage to the natural environment and health. Average genome size in a community is critical for shedding light on microbiome’s functional response to pollution stress within an environment. Here, microcosms under different concentrations were performed to evaluate the selection of PAHs stress on the average genome size in a community. We found the distinct communities of significantly larger genome size w...     

用EXAFS研究Zn在水锰矿上的吸附-解吸机理

用延展X光吸收精细结构光谱(EXAFS)研究了重金属Zn(Ⅱ)在水锰矿(γ-MnOOH)上吸附产物的微观结构及其吸附机理.结果表明,Zn(Ⅱ)-水锰矿体系中(pH 7.5,0.1mol/LNaNO₃介质,25℃),Zn²⁺主要是通过共用水合Zn²⁺的O原子及水锰矿表面上的O原子形成Zn-O键,从而结合到水锰矿固体表面上的.平均Zn-O原子间距为1.998±0.010 A(n=3).这个Zn-O键键长是六配位的Zn(H₂O)²⁺₆及其水解产物四配位的Zn(OH)₂或Zn(OH)₄^2-各以一定比例混合吸附于水锰矿表面而形成的.同时,对第二配位层(Zn-Mn相互作用)的EXAFS图谱分析证明存在2个典型的Zn-Mn原子间距,即R₁=3.08±0.024A(n=3)和R2=3.54±0.018 A(n=3).这2个Zn-Mn原子距分别对应于水锰矿结构单元MnO6八面体与Zn水合离子ZnO多面体结合的2种方式,即共用2个O原子的边-边结合与共用1个O原子的角-角结合.边-边结合是较强的吸附位,Zn-Mn原子距较短(R₁=3.08A),吸附较不可逆.角-角结合是较弱的吸附位,Zn-Mn原子距较长(R₂=3.54A),吸附较为可逆.这一结果从微观上证明了亚稳平衡态吸附理论(MEA理论)的基本假设,即具有相同吸附密度的同一吸附质由于吸附力强弱以及微观构型的不同可具有不同的化学位,因而证明了修正传统吸附热力学的基本假设(吸附密度为热力学状态函数)的必要性.宏观的吸附-解吸热力学实验表明Zn(Ⅱ)在水锰矿上的吸附是不可逆的,EXAFS结果指出这种不可逆性主要是由Zn水合离子中ZnO多面体与水锰矿结构单元MnO₆八面体之间的边-边结合所导致的.     

生物沸石床污水脱氮效果及机理

研究了生物沸石床对模拟村镇生活污水中各形态氮及COD等污染物的去除效果结果表明,生物沸石床对NH₃^--N去除效果明显且稳定,去除率大于95%,对NO₃^--N的去除则受水力停留时间的影响较大从机理分析,生物沸石对NH₃-N的去除主要依靠化学吸附、离子交换以及生物硝化的协同作用,而对NO₃^--N的去除主要依赖反硝化作用.生物沸石的硝化作用明显,并受溶解氧浓度限制,沸石床中部沸石硝化强度只有表层沸石的1/2;其反硝化能力则随实验条件中C/N的不同而变化明显,当COD/TN=5时,反硝化作用最强,在时间变化规律上,前6h反硝化速率最大.     

Effects of alfalfa coverage on runoff, erosion and hydraulic characteristics of overland flow on loess slope plots

An evaluation of the interactions between vegetation, overland and soil erosion can provide valuable insight for the conservation of soil and water. An experiment was conducted to study water infiltration, runoff generation process, rate of sediment erosion, and hydrodynamic characteristics of overland flow from a sloping hillside with different draw-off discharges from alfalfa and control plots with 20° slope. The effect of alfalfa on runoff and sediment transport reduction was quantitatively analyzed. Alfalfa was discussed for its ability to reduce the overland flow scouring force or change the runoff movement. Compared to the bare-soil plots, alfalfa plots generated a 1.77 times increase in infiltration rate. Furthermore, the down-slope water infiltration rate for the bare soil plots was higher than in the up-slope, while the opposite was found in the alfalfa plots. In addition, alfalfa had a significant effect on runoff and sediment yield. In comparison to the control, the runoff coefficient and sediment transportation rate decreased by 28.3% and 78.4% in the grass slope, respectively. The runoff generated from the alfalfa and bare-soil plots had similar trends with an initial increase and subsequent leveling to a steady-state rate. The transport of sediment reduced with time as a consequence of the depletion of loose surface materials. The maximum sediment concentration was recorded within the first few minutes of each event. The alfalfa plots had subcritical flow while the bare-soil plots had supercritical flow, which indicate that the capability of the alfalfa slope for resisting soil erosion and sediment movement was greater than for bare soil plots. Moreover, the flow resistance coefficient and roughness coefficient for the alfalfa plots were both higher than for the bare-soil plots, which indicate that overland flow in alfalfa plots had retarded and was blocked, and the flow energy along the runoff path had gradually dissipated. Finally, the ability to erode and transport sediment had decreased.     

Environmental dispersivity in free-water-surface-effect dominated wetland: multi-scale analysis

Distinct from the case with width-dominated shallow wetland flows, the longitudinal evolution of contaminant concentration in the most-typical pattern of wetland as dominated by free-water-surface-effect is characterized by a multi-scale analysis in the present study. An environmental dispersion model for the evolution of the mean concentration is deduced as an extension of Taylor's classical formulation by Mei’s multi-scale analysis. Corresponding environmental dispersivity is found identical to that determined by the method of concentration moments.     

Influence of Polyol Plasticizers on the Properties of Polyvinyl Alcohol Films Fabricated by Melt Processing

In this work, high-alcoholysis polyvinyl alcohol (PVA) films were fabricated by melt processing and the plasticizing effect of compound polyol plasticizers on PVA were investigated with X-ray diffraction (XRD), differential scanning calorimetry (DSC), rheological measurements, mechanical tests etc. Hydrogen bonding interactions occurred between PVA and plasticizer. With the increase of plasticizer, the flowability of PVA was improved and reached the maximum value at the plasticizer of 20%. Glass transition temperature (T _g) and melting point (T _m) decreased with the increase of plasticizer content. For the heterogeneous nucleation effect of plasticizer, new polymorph of PVA formed. The viscosity was sensitive to the shear rates. The incorporation of plasticizers into PVA resulted in the increase of elongation at break and impact strength, as well as the decrease of tensile strength.     

Removal of methylene blue by coupling black carbon adsorption with TiO2 photodegradation

In this study, the removal of methylene blue (MB) by the coupling of black carbon (BC) and TiO₂ was investigated. The effects of different parameters such as catalyst dose, sorbent, initial concentrations of dye, pH of the solutions, recycles on discoloration, and chemical oxidation demand (COD) reduction of MB were monitored to optimize the reaction conditions. The discoloration and COD conversation rate of MB obtained by the coupling process were 100% after 90?min irradiation. The synergistic effect of MB-adsorption on BC followed by degradation through TiO₂ photocatalysis was proved by FT–IR spectrophotometer. The BC as by-product of natural materials is a promising adsorbent for waste water treatment.     

Factors influencing sexual cannibalism and its benefit to fecundity and offspring survival in the wolf spider Pardosa pseudoannulata (Araneae: Lycosidae)

Sexual cannibalism is hypothesized to have evolved as a way to obtain a high-quality meal, as an extreme mate choice or as a consequence of female aggressive spillover. Here, we examined underlying factors likely to influence sexual cannibalism in the wolf spider Pardosa pseudoannulata (Bösenberg & Strand, 1906) from China, including mating status, female egg-laid status, female hunger level, female adult age and mate size dimorphism. The results showed that about 10 % of P. pseudoannulata virgin females cannibalized the approaching males before mating and that 28 % of P. pseudoannulata virgin females immediately cannibalized the males after mating. No incidents of sexual cannibalism during copulation were observed. Before mating, previously mated females and starved females tended to engage in significantly higher rates of attacks compared to virgin and well-fed females. Females that had laid egg sacs tended to engage in a significantly higher rate of attacks and sexual cannibalism than virgin females before mating. Regardless of pre- or post-mating, there was a strong positive relationship between mate size dimorphism and the occurrence of sexual cannibalism. We also tested the effects of sexual cannibalism on the fecundity of cannibalistic females and the survival of their offspring. Our results indicated that sexual cannibalism affected positively the offspring survival of cannibalistic females, but not fecundity. Our findings support the hypothesis that sexual cannibalism has evolved as an adaptive component of female foraging strategy and that it benefits offspring survival as a result of paternal investment.