Schäfer Dirk, Köber Ralf, Dahmke Andreas
Institut für Geowissenschaften, Christian-Albrechts-Universität zu Kiel, 24098 Kiel, Germany.
J Contam Hydrol. 2003 Sep;65(3-4):183-202. doi: 10.1016/S0169-7722(02)00239-5.
The successful dechlorination of mixtures of chlorinated hydrocarbons with zero-valent metals requires information concerning the kinetics of simultaneous degradation of different contaminants. This includes intraspecies competitive effects (loading of the reactive iron surface by a single contaminant) as well as interspecies competition of several contaminants for the reactive sites available. In columns packed with zero-valent iron, the degradation behaviour of trichloroethylene (TCE), cis-dichloroethylene (DCE) and mixtures of both was measured in order to investigate interspecies competition. Although a decreasing rate of dechlorination is to be expected, when several degradable substances compete for the reactive sites on the iron surface, TCE degradation is nearly unaffected by the presence of cis-DCE. In contrast, cis-DCE degradation rates decrease significantly when TCE is added. A new modelling approach is developed in order to identify and quantify the observed competitive effects. The numerical model TBC (Transport, Biochemistry and Chemistry, Schäfer et al., 1998a) is used to describe adsorption, desorption and dechlorination in a mechanistic way. Adsorption and degradation of a contaminant based on a limited number of reactive sites leads to a combined zero- and first-order degradation kinetics for high and low concentrations, respectively. The adsorption of several contaminants with different sorption parameters to a limited reactive surface causes interspecies competition. The reaction scheme and the parameters required are successfully transferred from Arnold and Roberts (2000b) to the model TBC. The degradation behaviour of the mixed contamination observed in the column experiments can be related to the adsorption properties of TCE and cis-DCE. By predicting the degradation of the single substances TCE and cis-DCE as well as mixtures of both, the calibrated model is used to investigate the effects of interspecies competition on the design of permeable reactive iron barriers. Even if TCE is present in only small concentrations (>3% of molar cis-DCE concentration) it is the contaminant limiting the residence time and the required thickness of the iron barrier.
用零价金属对氯代烃混合物成功进行脱氯，需要有关不同污染物同时降解动力学的信息。这包括种内竞争效应（单一污染物对活性铁表面的负载）以及几种污染物对可用反应位点的种间竞争。在填充零价铁的柱中，测量了三氯乙烯（TCE）、顺式二氯乙烯（DCE）及其混合物的降解行为，以研究种间竞争。尽管当几种可降解物质竞争铁表面的反应位点时，脱氯速率预计会降低，但TCE的降解几乎不受顺式DCE存在的影响。相反，添加TCE时，顺式DCE的降解速率显著降低。为了识别和量化观察到的竞争效应，开发了一种新的建模方法。数值模型TBC（传输、生物化学和化学，Schäfer等人，1998a）用于以机理方式描述吸附、解吸和脱氯。基于有限数量的反应位点，污染物的吸附和降解分别导致高浓度和低浓度下的零级和一级组合降解动力学。几种具有不同吸附参数的污染物吸附到有限的反应表面会导致种间竞争。反应方案和所需参数已成功从Arnold和Roberts（2000b）转移到模型TBC。柱实验中观察到的混合污染物的降解行为与TCE和顺式DCE的吸附特性有关。通过预测单一物质TCE和顺式DCE以及两者混合物的降解，校准后的模型用于研究种间竞争对可渗透活性铁屏障设计的影响。即使TCE仅以低浓度存在（>顺式DCE摩尔浓度的3%），它也是限制铁屏障停留时间和所需厚度的污染物。
