Bioremediation in situ of an alkaline soil polluted with heavy metals

An experimental plot consisting of alkaline soil heavily polluted with heavy metals (copper, zinc, cadmium) was treated in situ by stimulating the activity of the indigenous soil microflora, which contained different metal-solubilizing microorganisms. This was achieved by adding to the soil solid biodegradable organic substrates (cow manure, plant compost, straw), zeolite saturated with ammonium phosphate and aqueous solution containing acetate, lactate and magnesium chloride. An efficient removal of the above-mentioned heavy metals was achieved via the drainage water and their residual contents in the soil decreased to below the relevant permissible levels within 18 months of treatment. The metals were solubilized mainly as complexes with the organic acids added by the irrigating water solutions or secreted by the indigenous heterotrophic microorganisms, The effluents containing dissolved metals were efficiently treated by means of a wetland constructed near to the experimental plot.