Biogeochemistry of two types of permeable reactive barriers, organic carbon and iron-bearing organic carbon for mine drainage treatment: Column experiments

Permeable reactive barriers (PRBs) are an alternative technology to treat mine drainage containing sulfate and heavy metals. Two column experiments were conducted to assess the suitability of an organic carbon (OC) based reactive mixture and an Fe⁰-bearing organic carbon (FeOC) based reactive mixture, under controlled groundwater flow conditions. The organic carbon mixture contains about 30% (volume) organic carbon (composted leaf mulch) and 70% (volume) sand and gravel. The Fe⁰-bearing organic carbon mixture contains 10% (volume) zero-valent iron, 20% (volume) organic carbon, 10% (volume) limestone, and 60% (volume) sand and gravel. Simulated groundwater containing 380 ppm sulfate, 5 ppm As, and 0.5 ppm Sb was passed through the columns at flow rates of 64 (the OC column) and 62 (the FeOC column) ml d^− 1, which are equivalent to 0.79 (the OC column) and 0.78 (the FeOC column) pore volumes (PVs) per week or 0.046 m d^− 1 for both columns. The OC column showed an initial sulfate reduction rate of 0.4 µmol g (OC)^− 1 d^− 1 and exhausted its capacity to promote sulfate reduction after 30 PVs, or 9 months of flow. The FeOC column sustained a relatively constant sulfate reduction rate of 0.9 µmol g (OC)^− 1 d^− 1 for at least 65 PVs (17 months). In the FeOC column, the δ³⁴S values increase with the decreasing sulfate concentration. The δ³⁴S fractionation follows a Rayleigh fractionation model with an enrichment factor of 21.6‰. The performance decline of the OC column was caused by the depletion of substrate or electron donor. The cathodic production of H₂ by anaerobic corrosion of Fe probably sustained a higher level of SRB activity in the FeOC column. These results suggest that zero-valent iron can be used to provide an electron donor in sulfate reducing PRBs. A sharp increase in the δ¹³C value of the dissolved inorganic carbon and a decrease in the concentration of HCO₃⁻ indicate that hydrogenotrophic methanogenesis is occurring in the first 15 cm of the FeOC column.     

Variation of crack intensity factor in three compacted clay liners exposed to annual cycle of atmospheric conditions with and without geotextile cover

Performance of compacted clay liners commonly used as landfill barrier systems can be subject to decline in terms of hydraulic conductivity if left exposed to atmospheric conditions for an extended period of time prior to placement of overlaying layers. The resulting desiccation cracking can lead to increased hydraulic conductivity. Desiccation crack intensity was studied for three clayey soils commonly used for construction of landfill barrier system in a relatively large scale test setup exposed to real time atmospheric conditions over a complete annual cycle. A white separator geotextile cover was presumed to be capable of reducing the intensity of desiccation cracking through absorbing and maintaining higher amounts of moisture and reducing the temperature of the soil surface in comparison to a directly exposed soil surface. Desiccation cracking was monitored using a digital imaging technique for three compacted clay liners in two sets, one open to air and the second covered with the white geotextile. Crack intensity factor approached a relatively stable phase after certain cycles corresponding to atmospheric dry wet cycles. The results indicated that the white separator geotextile was capable of reducing the crack intensity factor by 37.4–45.9% throughout the experiment including the cyclic phase of desiccation cracking. During the stable phase, the maximum reduction in crack intensity factor of 90.4% as a result of applying geotextile cover was observed for the soil with the lowest plastic index and clay content and therefore the lowest magnitude of crack intensity factor. The other two soils with similar clay content but different plastic index showed 23.6% and 52.2% reductions in crack intensity factor after cyclic phase when covered with geotextile.     

介质阻挡放电对氯苯的降解特性及其产物分析

鉴于生物法对难生物降解性、低水溶性的VOCs去除效果不佳,因此开发高效的前处理技术来提高生物法的净化能力已成为新的热点.本实验以生物可降解性差的氯苯为目标污染物,以介质阻挡放电低温等离子体(DBD)为生物法的前处理技术,通过调节DBD反应器的工艺参数,研究其对氯苯的降解效果,考察了进气浓度、停留时间、湿度、峰值电压等因素对去除率的影响,并对尾气进行初步分析.结果表明,DBD能有效去除氯苯废气,氯苯去除率随峰值电压的升高而增大;当电压≥12k V时,停留时间对氯苯的降解影响较小;65%~75%为氯苯降解的最佳湿度范围.通过产物分析,发现产物的种类和浓度随着放电电压的升高而增多增大,主要是以有机酸类和氯代烃为主.产物的水溶性较好;可生化性随着电压升高而增强;随电压升高,小球藻受到的生长抑制作用越来越小,当电压达到20k V时,反而有促进作用.降解过程中产生的O3量随着电压的升高而增多,并且在同一电压下臭氧产生量随着湿度的增大而增多.     

Toluene decomposition performance and NOx by-product formation during a DBD-catalyst process

Characteristics of toluene decomposition and formation of nitrogen oxide (NO_x) by-products were investigated in a dielectric barrier discharge (DBD) reactor with/without catalyst at room temperature and atmospheric pressure. Four kinds of metal oxides, i.e., manganese oxide (MnOx), iron oxide (FeOx), cobalt oxide (CoOx) and copper oxide (CuO), supported on Al₂O₃/nickel foam, were used as catalysts. It was found that introducing catalysts could improve toluene removal efficiency, promote decomposition of by-product ozone and enhance CO₂ selectivity. In addition,NO_xwas suppressedwith the decrease of specific energy density (SED) and the increase of humidity, gas flow rate and toluene concentration, or catalyst introduction. Among the four kinds of catalysts, the CuO catalyst showed the best performance in NO_x suppression. The MnOx catalyst exhibited the lowest concentration of O₃ and highest CO₂ selectivity but the highest concentration of NOx. A possible pathway for NOx production in DBD was discussed. The contributions of oxygen active species and hydroxyl radicals are dominant in NOx suppression.     

公路交通噪声防治措施

随着交通运输业的发展及公路等级的不断提高,公路交通噪声越来越引起人们的关注,因此,解决公路交通噪声污染成为一个急待解决的问题,本文论述公路交通噪声造成的危害,并有针对性地提出降低公路交通噪声防治措施。     

企业财务危机预警判断分析方法研究

财务危机是威胁企业持续经营的根本性危机,它不是突然而至,分为潜伏期、爆发期、成长期和解决期四个阶段逐步积累过程.根据不同阶段的企业财务状况,把爱德华.阿特曼Z值计分模型和不同时期的相关财务指标结合起来,运用定量和定性相结合的分析方法,判断分析企业的财务危机的级别,从而采取相应的措施,以利于规避财务风险.     

全球经济一体化中的环境壁垒与我国环境和贸易政策选择

本文纵观全球经济贸易格局和环境问题特点,指出了环境壁垒是影响全球贸易和环境的重要因素,分析了环境壁垒产生的本质,提出了国际贸易的新形势下我国如何实现可持续经济发展的贸易和环境政策。     

Saturated and Unsaturated Water Flow in Inclined Porous Media

This paper considers the two-dimensional saturated and unsaturated flow of water through inclined porous media, namely a waste dump or hill slope. Since the partial differential equation governing this water flow transforms from being parabolic to elliptic as the water flow varies from unsaturated to saturated, an iterative, finite differencing scheme is used to develop a numerical solution. The model can be used to investigate the effects that hill slope angle, depth of soil cover and hilltop width have on water accumulation in the dump and the time required for saturation to occur at different areas in the dump domain. The accuracy and reliability of the computer based solution is tested for two different boundary conditions – (1) no flow on all boundaries (i.e., the internal redistribution of soil moisture to steady state) and (2) a constant rainfall flux on the dump surface. Numerical studies then show the effects of changing the hill slope angle, depth of layer, and dump geometry on the flow characteristics in the dump.     

历史上的一次溃决洪水--1482年沁河流域大洪水

据沁河流域九女台洪水题刻水位及相关历史文献记载,沁河流域1482年洪水洪峰流量极大,历时甚长,与该流域一般洪水过程的差异迥然.通过地貌调查,并利用14C测年等方法,对沁河九女台河段进行了详细研究,发现其1482年高洪水位是梯沟口泥石流-崩塌堆积物堰塞沁河主河道的结果.当年由于降雨,使梯沟流域发生泥石流,并导致沟口右岸岩壁崩塌,形成堰塞坝,造成沁河河道阻塞,过水断面减小,九女台附近河段水位壅高,并保持了近40天的时间,堰塞坝最终溃决,导致沁河下游怀庆府发生严重的洪水灾害.