Soil bioremediation: Combination of earthworms and compost for the ecological remediation of a hydrocarbon polluted soil

The present investigation, carried out in laboratory microcosms, regards the effects of some bioremediation treatments of a polluted soil and the use of specific parameters to study the evolution of biochemical processes which take place in the soil decontamination. The bioremediation treatments were the following: 1) a mixture of microorganisms-enzymes-nutrients (MEN); 2); compost alone (C); 3) compost with earthworms (Eisenia fetida) (CL) and (4) control soil (without treatment) (BN). Chemical, physico-chemical, biological and biochemical parameters were determined to study the soil metabolic processes in order to assess the efficiency of the bioremediation process involved in the degradation of hydrocarbons. The study showed an intense microbiological activity expressed as carbon dioxide evolution during the time, with a tendency to stabilize at the end of the experiments. The highest carbon dioxide release was found in the two compost treatments, showing the availability of organic substrate characterising the compost. The organic substrate reduction during the time caused a decrease of hydrolytic enzyme activities representative of Carbon (beta-glucosidase), Nitrogen (protease) and Phosphorus (phosphatase) cycles. However, the enzyme activities showed their highest values in the treatments with compost. Finally, the greatest reduction of hydrocarbons was found in the treatments with compost, in particular with earthworms that also contributed to regulate the biochemical equilibrium of the soil.