零价铁降解水中氯代烃的实验室研究

由于氯代有机溶剂的大量使用和使用氯气对饮用水消毒 ,致使四氯化碳 (CT)和四氯乙烯 (PCE)成为地下水和饮用水中常见的污染物 .利用廉价铁屑对CT和PCE进行还原性脱氯 ,对其动力学过程进行初步研究 ,并对影响反应速率的因素进行探讨 .结果表明 ,零价铁对氯代烃有明显的脱氯作用 ,相同氯代程度的烷烃和烯烃 ,烷烃的脱氯速度快 ,反应符合一级反应动力学方程 ,反应是准一级反应 ,反应速率受到传质速率即零价铁比表面积的影响 .     

A modified light transmission visualization method for DNAPL saturation measurements in 2-D models

In this research, a light transmission visualization (LTV) method was used to quantify dense non-aqueous phase liquids (DNAPL) saturation in two-dimensional (2-D), two fluid phase systems. The method is an expansion of earlier LTV methods and takes into account both absorption and refraction light theories. Based on this method, DNAPL and water saturations can rapidly be obtained point wise across sand-packed 2-D flow chambers without the need to develop a calibration curve. A single point calibration step is, however, needed when dyed DNAPL is used to account for the change in the transmission factor at the dyed DNAPL–water interface. The method was applied to measure, for the first time, undyed DNAPL saturation in small 2-D chambers. Known amounts of DNAPL, modeled by tetrachloroethylene (PCE), were added to the chamber and these amounts were compared to results obtained by this LTV method. Strong correlation existed between results obtained based on this method and the known PCE amounts with an R² value of 0.993. Similar experiments conducted using dyed PCE showed a stronger correlation between results obtained by this LTV method and the known amounts of dyed PCE added to the chamber with an R² value of 0.999. The method was also used to measure dyed PCE saturation in a large 2-D model following sparging experiments. Results obtained from image analyses following each sparging event were compared to results obtained by two independent techniques, namely gas chromatography–mass spectrometry (GC/MS) analyses and carbon column extraction. There was a good agreement between the results obtained by this LTV method and those obtained by the two independent techniques when experiments were carried out under stable light source conditions and errors in mass balance were minor. The method presented here can be expanded to measure fluid contents in three fluid phase systems and provide a non-destructive, non-intrusive tool to investigate changes in DNAPL architecture and flow characteristics in laboratory experiments.     

Vertical variability of PCE sorption in the lacustrine clays of Mexico City

 A surficial clay aquitard extends through the urban area where Mexico City is located. It has been assumed to function as a protective layer to the underlying aquifer that provides 42 m³/s out of 63 m³/s of water used by 18 million inhabitants. To provide such protection, the aquitard must be impermeable to water flow and, ideally, have a significant capacity to sorb contaminants. The latter aspect was addressed, studying the vertical variability of sorption of perchloroethylene (PCE), a widely used organic compound considered to pose health risks in groundwater. Batch sorption tests were used and the clay-rich strata in the depth interval from 8 to 75 m were studied. The results suggest that sorption depends mainly on the fraction of organic carbon (f_oc) present in the clayey materials. The sorption data were fit to the linear and Freundlich models; many strata could be fit well by either model, while some strata were distinctly non-linear. The linear isotherms showed a mean value of 32.8 ml/g, and the Freundlich isotherm 96.6 ml/g, confirming that the clay-rich media have significant sorption capacity for PCE. From the environmental perspective the clay-rich materials are serving as protection to the groundwater system. Received: 2 November 1998 · Accepted: 15 February 1999     

苯、甲苯对粒状铁去除四氯乙烯影响的柱实验研究

挥发性氯代烃和石油烃类污染是地下水中最常见的混合污染类型,而且这两类污染物毒性极强,对人类危害非常严重。文中选取具有代表性的四氯乙烯、苯和甲苯为研究对象,采用柱实验的方法研究苯和甲苯在粒状铁反应系统中吸附平衡后,对粒状铁去除四氯乙烯的机理及反应动力学的影响。在实验装置运行的过程中,苯、甲苯和四氯乙烯的浓度始终控制在2mg/L左右的水平。实验结果表明:苯或甲苯的存在对被还原的产物组成没有影响,主要氯代中间产物均为TCE、1,1-DCE、cis-1,2-DCE和VC,但组成比例略有不同。苯和甲苯的存在对去除速率有影响,即苯对四氯乙烯的去除有促进作用,去除速率平均提高13.5%;而甲苯则抑制四氯乙烯的去除,去除速率平均降低13.8%。对比控制柱,苯和甲苯存在时对出水水化学变化的影响没有明显差异。     

纳米镍-铁去除四氯乙烯的影响因素

氯代烃是地下水中最常检出的有机污染物之一,传统的处理方法需要很长时间与大量经费。本文利用批实验的研究方法以四氯乙烯(PCE)为目标污染物,研究纳米镍铁在去除PCE过程中的影响因素。实验结果表明,暴露后的纳米镍铁脱氯速率比不暴露时速率降低约4倍;反应温度是影响反应速率的重要因素之一,每升高10℃,反应速率常数kSA提高2～3倍;在一定范围内,镍/铁质量比越高,越利于脱氯反应的快速进行,镍/铁的质量比为8%左右时,对氯代烃脱氯速率最快;反应液中的溶解氧不利于纳米颗粒对氯代烃的降解。