In situ sequential treatment of a mixed contaminant plume

Groundwater plumes often contain a mixture of contaminants that cannot easily be remediated in situ using a single technology. The purpose of this research was to evaluate an in situ treatment sequence for the control of a mixed organic plume (chlorinated ethenes and petroleum hydrocarbons) within a Funnel-and-Gate. A shallow plume located in the unconfined aquifer at Alameda Point, CA, was found to contain up to 218,000 μg/l of cis-1,2 dichloroethene (cDCE), 16,000 μg/l of vinyl chloride (VC) and <1000 μg/l of 1,1 dichloroethene (1,1 DCE), trans-1,2 dichloroethene (trans-1,2 DCE) and trichloroethene (TCE). Total benzene, toluene, ethylbenzene and xylenes (BTEX) concentrations were <10,000 μg/l. Contaminated groundwater was funneled into a gate, 3.0 m wide, 4.5 m long and 6.0 m deep (keyed into the underlying aquitard) where treatment occurred. The initial gate segment consisted of granular iron, for the reductive dechlorination of the higher chlorinated ethenes. The second segment, the biosparge zone, promoted aerobic biodegradation of petroleum hydrocarbons and any remaining lesser-chlorinated compounds, stimulated by dissolved oxygen (DO) and carbon dioxide (CO₂) additions via an in situ sparge system (CO₂ was used to neutralize the high pH produced from reactions in the iron wall). Groundwater was drawn through the gate by pumping two wells located at the sealed, downgradient, end. Over a 4-month period an estimated 1350 g of cDCE flowed into the treatment gate and the iron wall removed 1230 g, or 91% of the mass. The influent mass of VC was 572 g and the iron wall removed 535 g, corresponding to 94% mass removal. The other chlorinated ethenes had significantly lower influent masses (3 to 108 g) and the iron wall removed the majority of the mass resulting in >96% mass removal for any of the compounds. In spite of these high removal percentages, laboratory column tests indicated that at these levels of chlorinated contaminants, surface saturation of the iron grains likely contributed to lower than expected reaction rates. In the biosparge zone, mass removal of cDCE appeared to occur predominantly by biodegradation (65%) with volatilization (35%) being an important secondary process. The dominant removal process for VC was volatilization (70%) although significant biodegradation was also indicated (30%). Laboratory microcosm results confirmed the potential for aerobic biodegradation of cDCE and VC. When average influent field concentrations for cDCE and VC were 220,000 and 46,000 μg/l, respectively, the sequential treatment unit removed 99.6% of the total mass and when the influent concentrations decreased to 26,000 and 19,000 μg/l for cDCE and VC, respectively, >99.9% removal within the treatment gate was attained. BTEX compounds were found to be significantly retarded in the iron treatment zone. Although they did eventually break through the granular iron, and into the gravel transition zone, none of these compounds was detected in the biosparge zone. No noticeable interferences between the anaerobic (reductive) and aerobic parts of the system occurred during testing. The results of this experiment show that in situ treatment sequences are viable, although further work is needed to optimize performance.     

工业废水中测定六价铬的预处理技术

根据复合絮凝剂与阳离子交换树脂两者在分离与处理技术上所起的不同作用 ,提出了将两法联合用作工业废水中测定Cr6 的预处理技术 ,通过一系列条件试验 ,确定最佳预处理条件。结果表明 ,该法具有去色、去浊率高 ,分离效果佳 ,排除干扰离子能力强 ,分析样品重现性好 ,准确度高 ,操作简便、快捷的优点。     

PRB技术修复铬污染地下水的试验研究

以铬污染地下水为研究对象,用零价铁作为反应介质设计了可渗透反应墙(PRB),对零价铁处理铬污染地下水的处理效果和长期稳定性进行了研究。对不同粒径的铁粉处理效果进行对比,发现铁粉粒径越小,处理效果越好。用铁粉作为PRB反应介质,对PRB处理铬污染地下水的长期稳定性进行了研究。试验结果表明,采用Fe0-PRB原位技术处理铬污染地下水,铁粉粒径越小处理废水的水质越好,但介质粒径越小,反应器渗透系数越小,处理水量显著减少;且铁粉在处理含铬废水时生成了大量的难溶化合物,容易造成填料堵塞,导致铁粉利用效率不高。因此有必要研制铁粉复合填料,增大填料的渗透性,提高填料处理含铬废水时铁粉的利用效率。     

Using chemical models for evaluating the geochemical confinement capacity of a geological barrier application to the Centre de Stockage de l'Aube (France)

The feasibility of using a chemical reaction-based approach for evaluating and modelling the role of adsorption reactions in determining the geochernical confinement capacity of natural geological barriers is being studied as part of an on-going R & D programme. The confined superficial aquifer underlying the Centre de Stockage de l'Aube facility, a geological barrier for this site, has been used as a case study with the following aims. First, development of a site characterisation protocol and demonstration of its use to determine the principal geochemical characteristics of aquifer materials using batch experiments and to represent the information obtained in terms of a chemical model. The experimental results obtained for Ni²⁺ partitioning as a function of total Ni, pH, total Ca and total solid can be satisfactorily represented in terms of reactions with an ion exchange site and a single amphoteric surface hydroxyl site with ferrihydrite reaction constants. A second objective is the incorporation of the reactions in a coupled geochemistry/transport code, and to verify the applicability of the coupled code predictions for Ni²⁺ mass transfer by comparison with the results obtained during column tracer experiments. The breakthrough curve and equilibrium solid phase Ni loading, predicted by a one-dimensional coupled model for a column tracer experiment, agree closely with observed data.Additional studies are underway to reduce model conditionality, to extend the adsorption model to other analogue cations and anions, to incorporate the effect of natural organic matter and to take into consideration precipitation/dissolution of amorphous Fe surface phases.     

TiO2/ZnO光催化降解四环素的研究

以太阳光、汞灯为光源，TiO2/ZnO复合半导体为催化剂处理四环素溶液，探讨了催化剂的配比、溶液体积、光照时间、pH、初始浓度、光强等6种因素对光催化活性的影响，比较了汞灯和太阳光作光源时的光催化效果，结果表明，用太阳光作光源时光催化效果也较好。     

绿色贸易壁垒与中国出口贸易

介绍绿色贸易壁垒的主要内容，分析绿色贸易壁垒对中国出口贸易的影响，并提出了一系列的对应策略与措施。     

湖南旅游电子商务发展的理性分析

近几年兴起的旅游电子商务是旅游经济的一种新态势,中国旅游网站的建设始于1996年,湖南旅游网站也随之建立.目前,旅游电子商务正在对湖南旅游市场固有的市场壁垒带来革命性的冲击,新的市场关注点正在涌现.通过对湖南旅游电子商务发展的现状、障碍、对策进行了理性分析,而旅游电子商务本身更须不断努力.     

Renewable energy resources and technologies in Nigeria: present situation, future prospects and policy framework

Nigeria is endowed with abundant energy resources, both conventional and renewable, whichprovide her with immense capacity to develop an effective national energy plan. However, introduction of renewable energyresources into the nation's energy mix have implications on itsenergy budget. The national energy supply system has been projected intothe future using MARKAL, a large scale linear optimization model.However, this model may not be absolutely representative of the highlynon-linear future of renewable energy. Results of the model reveal that under onlya least cost constraint, only large hydro power technology is the prominentcommercial renewable energy technology in the electricity supply mix of thecountry. Despite the immense solar energy potentials available, solar electricity generation is attractive only under severeCO2 emissions mitigation of the nation's energy supply system. Similarly, the penetration of small-scale hydro power technology in theelectricity supply mix is favoured only under CO₂ emissionsconstraints. Due to economy of scale, large hydropower technology takes the lion share of all the commercial renewableenergy resources share for electricity generation under any CO₂emissions constraint. These analyses reveal that some barriers exist to thedevelopment and penetration of renewable energy resources electricity production in Nigeria's energy supplysystem. Barriers and possible strategies to overcome them arediscussed. Intensive efforts and realistic approachtowards energy supply system in the country will have to be adopted inorder to adequately exploit renewable energy resources and technologiesfor economic growth and development.