Changes in metal availability during sediment oxidation and the correlation with the immobilization potential.

Fractionation of metals (Pb, Cd, Ni, Zn, Cu and Cr) in severely contaminated sediment has been investigated to determine its speciation and eco-toxic potential at the beginning of the experiment and after 18 months of sediment oxidation. Pb, Ni and Zn showed a high risk, while Cu, Cd and Cr showed low to medium risk at the beginning. Oxidation yielded an increased mobility of all metals apart from cadmium. The ratio of the simultaneously extracted metals (SEM) and acid volatile sulfides (AVS) was found to be >1. Semi-dynamic and toxicity characteristic leaching tests were conducted to assess the effectiveness of solidification/stabilization (S/S) thermal treatment with clay and long-term leaching behavior of these metals. A diffusion-based model was used to elucidate the controlling leaching mechanisms. Applied S/S thermal treatment was effective in immobilizing metals, irrespective of their different availability in the untreated samples. The controlling leaching mechanism appeared to be diffusion.

Kinetics of degradation of hydrocarbons in the contaminated soil layer.

This work presents kinetic parameters of the removal of hydrocarbons in the course of bioremediation of the soil contaminated with crude and oil derivatives, with special emphasis paid to polycyclic aromatic hydrocarbons. Bioremediation was carried out on a laboratory scale, with continuous and discontinuous recirculation of water through the soil column inoculated with the adapted bacterial population. Biodegradation of hydrocarbons can be described by the following equation--ln C = ln C0- kt--which is most often used in the literature to describe degradation of hydrocarbons, and by the equation--ln C = ln C0- kt0.5--which is determined on the basis of experimental data (except for pyrene and chrysene, for which a linear equation was used). A comparison of the two models showed a significant difference in the calculated remediation times, indicating that it is not realistic to expect a simple kinetic model to provide precise and accurate descriptions of concentrations during different seasons and in different environments. The results indicated that once contaminated with hydrocarbons, soil can be slowly brought to the previous state provided that no new contamination has occurred.