BIOTECHNOLOGIES FOR REMEDIATION OF SOILS POLLUTED WITH HEAVY METALS BY ACID MINE DRAINAGE
PLAMEN GEORGIEV*, STOYAN GROUDEV, IRENA SPASOVA, MARINA NICOLOVA
Department of Engineering Geoecology, University of Mining and Geology “St. Ivan Rilski”, Sofia Bulgaria
*Corresponding author: ps_georgiev@mgu.bg
Keywords: heavy metals, leaching, immobilization, soil
Abstract: Acid mine drainages (AMD) are generated as a result of bacterial oxidation of sulphides in the mining area. Acidic water pH, higher concentrations of iron, non-ferrous metals, radioactive or toxic elements are present, mainly as free ions highly toxic to organisms living in surrounding aquatic and terrestrial ecosystems, are the reason why AMD is regarded as one of the most complex environmental problems arising due to the human activity.
Remediation of AMD-affected soil was studied by means of two completely different biotechnological methods. The pollutants leaching from topsoil as a result of addition of S° and straw to the soil was the aim of the first method. As a result, growth and activity of sulfur-oxidizing bacteria and fungi were stimulated and due to the lowering soil pH and higher concentration of organic acids into the soil solutions, the soil pollutants were easily leached from the topsoil. At the end of soil remediation, the concentration of the soil pollutants was decreased below the relevant Maximum Admissible Concentrations (MAC) for heavy metals in soils. Soil reclamation was applied as a next stage with the aim to restore soil pH and increase the organic content of the soil.
The other method of soil remediation and reclamation was based on the pollutants’ immobilization into the topsoil. It was achieved by means of the addition of a mixture with C:P = 150:1 consisting of carbonate, hydroxyapatite (Ca10(PO4)6OH), compost, and montmorilonite. Due to the phosphate-releasing process and consumption of H+ by means of chemical and microbial processes, the heavy metals were precipitated as sparingly soluble phosphates and soil pH was increased to 6.18. As a result, the toxicity of AMD-affected soil to organisms was decreased between five to eight folds in comparison with non-treated soil.