Terrestrial microcosms in a feasibility study on the remediation of diesel-contaminated soils

Phytoremediation and bioremediation are site-specific processes, and feasibility studies should be performed as an initial step in scaling-up these processes. Soil microcosms can be a useful tool for investigating the efficiency of remediation alternatives under realistic conditions. In the present study, the degradation of diesel fuel in soil was studied in artificially assembled microcosms during a 180-day experiment. Microcosms consisted of soil columns seeded with a mix of Festuca arundinacea and Trifolium pratense into which earthworms were introduced and native soil microflora was used. Remediation assays were performed with different combinations of soil organisms' assemblages (micro-organisms, earthworms and plants) to determine the effects of these organisms and their interaction on diesel degradation. The microcosm system allowed for the study of the efficiency of remediation under field-relevant conditions. This system provided information about the dissipation of the pollutants as well as chemical leaching and possible toxic effects on the organisms during the remediation process. The decrease in soil hydrocarbon levels depended on the organisms' assemblage. Plants were not effective in the remediation of these soils despite their stimulation of microbial biomass. Conversely, earthworms had a beneficial impact on the dissipation of hydrocarbons that did not appear to be related to a generic improvement of plant or microbial activity. The grass species was more tolerant than the legume species to diesel fuel-contaminated soils. Leaching of hydrocarbons was negligible and independent of the organisms' assemblage.