Attenuation of methane and nonmethane organic compounds in landfill gas affected soils

Landfill gas (LFG) contains high concentrations of methane, which contributes to the greenhouse effect. LFG also contains aromatic hydrocarbons and chlorinated aliphatics, which, by emission to ambient air, can be a local health threat. In addition, chlorinated aliphatics may also influence the earth's ozone layer. The objectives of the study were to investigate the degradation of LFG constituents in LFG-affected soils, and to evaluate the importance of the degradation processes to the emission. High methane oxidation potentials were found in laboratory experiments at 25 degrees C. The degradation seemed to follow zero order reaction kinetics, and was 3-4 times slower at 10 degrees C than at 25 degrees C. High degradation rates for benzene and toluene were also observed. In soils sampled away from the landfill, where almost no LFG contamination had been observed, longer lag phases and lower degradation rates of the two aromatic hydrocarbons were observed. Slow cometabolic degradation of trichloroethylene (TCE) and 1,1,1-trichloroethane (TCA) was observed when methane was present in the batch experiments. The rates were much lower than the rates for the aromatic hydrocarbons. In the field at Skellingsted Landfill, Denmark, high methane emissions were observed in an area just outside the landfill area, probably as a result of the clay landfill covering, which has led to significant lateral migration of LFG. Indications of active methane oxidation in the field were observed by measuring soil gas profiles. By comparison of the results obtained in the laboratory with the field results, it is shown that degradation processes may have a significant effect on the emission of all the compounds studied. However, the subject needs much more attention.