A combined removal of oil, toxic metals and arsenic from contaminated soils

摘要

In the Tulenovo oil deposit, Northeastern Bulgaria, soils have been heavily contaminated with oil, toxic heavy metals (mainly lead and cadmium) and arsenic. A pilot scale operation for a combined removal of these pollutants from the soils was carried out using the heap technique. The soil remediation was based on the activity of both indigenous and laboratory-bred microorganisms which formed a stable community. The oil was degraded to non-toxic products, while the heavy metals and arsenic were solubilized mainly as complexes with secreted microbial metabolites and were removed from the heap by drainage waters percolating through the soil mass. The regular ploughing up of the soil, the injection of air, the addition of nutrients (ammonium and phosphate), the maintenance of water content in the range of about 30-35% and temperature of the soil were the most essential factors for enhancing the microbial growth and activity. The oil content in the heap was decreased from the initial 20-25 to less than 2 g/kg dry soil within 8 months of treatment (from the middle of March 1997 to the middle of November 1997). Simultaneously, the contents of lead, cadmium and arsenic were decreased below the relevant permissible levels.