Degradation of aromatic and chlorinated aliphatic hydrocarbons in the anaerobic part of the Grindsted Landfill leachate plume:: In situ microcosm and laboratory batch experiments

The fate of seven aromatic and four chlorinated aliphatic compounds was studied using in situ microcosm (ISM) and laboratory batch (LB) experiments performed at six distances along a flow line in the anaerobic leachate plume downgradient of the Grindsted Landfill, Denmark. The redox conditions were dominated by iron reduction in this part of the plume (15 to 60 m downgradient of the landfill); however, methanogenesis and sulfate reduction also took place closer to the landfill (15 to 45 m). Generally, goad accordance was found between the degradation of the compounds determined by the two experimental approaches, considering the limitations of the experimental periods (up to 220 days for the ISM and up to 537 days for the LB). Of the aromatic compounds, toluene, o- and m/p-xylene were degraded, while benzene, ethylbenzene, and naphthalene were not degraded, neither in the ISM nor in the LB at any distance from the landfill. All the chlorinated-aliphatic compounds, (TeCM, 1,1,1-TCA, PCE, and TCE) were degradable; however, the degradation potential for PCE and TCE depended on the distance from the landfill. For most compounds, both approaches gave results comparable to those of the natural gradient field injection experiment performed in the same plume. This suggests that laboratory batch experiments, which are easier to run than ISM experiments, may be a useful tool in determining the degradability of mono aromatic hydrocarbons and chlorinated aliphatic hydrocarbons under strongly anaerobic conditions in the investigation of natural attenuation in landfill leachate plumes.