Dermietzel, et al., reported in 1997 that until 1990 the Bitterfeld region was heavily polluted by mining, an obsolete chemical industry and the uncontrolled deposition of chemical wastes. The cessation of lignite-mining and open-pit drainage resulted in a rise of the groundwater followed by mobilization of contaminants, especially halogenated hydrocarbons. At the research area in Bitterfeld, only highly mobile chlorinated aliphatics and aromatics have been detected both in groundwater and sediments, especially in a lignite seam.
The modern analytical method of solid-phase micro extraction (SPME) was successfully applied to analysis of the pollution level of groundwater and sediments. The authors show that the lignite seam has accumulated large quantities of halogenated hydrocarbons and acts like a giant adsorption filter. The vertical pollution profiles of sediments and the distribution coefficients between lignite and groundwater at equilibrium conditions were determined for the key components. The results indicate that in addition to the adsorption processes, the microbiological degradation of aliphatic halocarbons occurs in the groundwater and within the lignite seam.
In the research area of Bitterfeld only soluble halocarbons were detected in groundwater and sediment, especially within the lignite seam. Exchange experiments in the water/lignite system by both adsorption from the liquid phase on lignite and desorption from the lignite into the water showed that the majority of contaminants are reversibly adsorbed within the lignite. Lignite/water distribution coefficients at equilibrium conditions were evaluated and showed an increasing trend from DCE to chlorobenzene and dichlorobenzenes. According to this, the DCE was transported through the lignite seam, whereas the majority of the more polar and less soluble dichlorobenzenes are adsorbed near the lignite seam border with clay.
The present pollution potential within the lignite seam is a result of the groundwater pollution in the past. Thus, the lignite is heavily polluted with trichloroethene, whereas the Quarternary groundwater is nearly free of it at present. This means that the long-term interaction between groundwater and coal has resulted in a different situation concerning aliphatic and aromatic halocarbons. The adsorbtion capacity of lignite for chlorobenzenes is not yet been exhausted and at the present level of groundwater contamination further adsorption will take place.
On the other hand the TCE content of the lignite is up to three orders of magnitude greater than the groundwater concentration. This means that the desorption of TCE from the lignite into the water has to be expected at equilibrium conditions. Adsorption/desorption processes under actual conditions are not so much thermo-dynamically controlled as subject to kinetic and hydrodynamic parameters. Furthermore, the high concentrations of DCE indicate that the microbiological degradation of TCE may be faster than the desorption rate of TCE from lignite. Thus, the actual impact of the lignite seam on the retardation and degradation of pollutants needs to be evaluated by additional kinetic simulation experiments - which are already underway.
Managed & Built by I2M Consulting, LLC | © 2010-
