Reclamation of land contaminated by heavy oil and diesel

CASE STUDY

Location: Municipality of Pescia, province of Pistoia – Italy
Implemented technology: landfarming with biostimulation and bioaugmentation

The following describes the application of landfarming technology in a case of contamination by heavy oils, operated by DND Biotech and commissioned by the Municipality of Pescia, Province of Pistoia. Following the flooding of the Pescia river, there was a leakage of hydrocarbons (heavy oil and diesel) from a deposit in the area. The hydrocarbons, transported by the waters, have contaminated with patchy distribution a large portion of the territory (for agricultural use) of the Municipality of Pescia, estimated at about 10 hectares of extension.

DND Biotech intervened with emergency safety measures (concerning water and land) to avoid the migration of contaminants to non-polluted areas. Subsequently, an environmental characterization was carried out aimed at defining the state of contamination of the areas concerned.

The application of landfarming technology was evaluated through pilot tests carried out on a laboratory scale. The fertilizers chosen were urea and superphosphate. A bioinoculum containing 80 bacterial strains was selected, including some of the most efficient microorganisms in the aerobic or optional demolition of the various hydrocarbons and compounds high molecular weight petroleum including:

▪ The Nocardia bacteria group, able to operate at all oxygen levels
▪ Different species of Pseudomonas, which produced the enzymes necessary for the oxidation of aromatic compounds, such as toluene and xylene. These bacteria are also able to metabolize phenols through oxidizing reactions.
▪ The Arthrobacter species, able to break down linear and complex molecules of hydrocarbons
▪ The Bacillus species, completing the action of the other bacteria
At the contaminated site, the soils contaminated by heavy hydrocarbons (about 1000 cubic meters) were removed and accumulated separately from the green fractions to be sent to the landfarming process.

The landfarming treatment was carried out using conventional management practices adopted in agricultural activities and in the composting of MSW (tillage, irrigation, fertilization), to promote bacterial growth and aerobic degradation of organic pollutants.

A waterproofed LTU (Landfarming Treatment Unit) area of 130 size was set up, with four 3m x 0.6 m x 115 m piles of contaminated soil. In addition to inoculation, for the purposes of the microbiological degradation of undesirable hydrocarbon substances have been guaranteed the correct ratios between nitrogen, phosphorus, potassium, and total organic carbon, adding enriching plant substances.

To ensure the right supply of oxygen, the piles were turned over on a weekly basis. To ensure the right level of humidity, the piles were irrigated (about 3 times a week) with a 360 ° nozzle system. The main operational parameters were monitored to assess the progress of the process.

As the following table indicates, the remediation target of 50 mg/kg (Italian legislation for residential use) for hydrocarbons concentration was reached in about three months, starting from an average concentration of 595 mg/kg.