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 stu died using in situ microcosm (ISM) and laboratory batch (LB) experiments pe rformed 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 downgradi ent of the landfill); however, methanogenesis and sulfate reduction also to ok place closer to the landfill (15 to 45 m). Generally, goad accordance wa s found between the degradation of the compounds determined by the two expe rimental approaches, considering the limitations of the experimental period s (up to 220 days for the ISM and up to 537 days for the LB). Of the aromat ic compounds, toluene, o- and m/p-xylene were degraded, while benzene, ethy lbenzene, and naphthalene were not degraded, neither in the ISM nor in the LB at any distance from the landfill. All the chlorinated-aliphatic compoun ds, (TeCM, 1,1,1-TCA, PCE, and TCE) were degradable; however, the degradati on potential for PCE and TCE depended on the distance from the landfill. Fo r most compounds, both approaches gave results comparable to those of the n atural gradient field injection experiment performed in the same plume. Thi s suggests that laboratory batch experiments, which are easier to run than ISM experiments, may be a useful tool in determining the degradability of m ono aromatic hydrocarbons and chlorinated aliphatic hydrocarbons under stro ngly anaerobic conditions in the investigation of natural attenuation in la ndfill leachate plumes.