RESUMEN
Earlier investigations on laboratory and pilot plant scale have shown the resort to microorganisms to be a practicable approach to the problem of purifying mineral dressing plant reject waters from residual flotation reagents and/or metal ions. In spite of the proven effectiveness of this method, one major drawback, namely the pathogenicity of some microorganisms, has so far hampered its application on a commercial scale. A research programme, aimed at developing a microbial reject water purification technique utilizing non-pathogenic strains was thus drawn up and is currently being implemented. Strains such as Bacillus subtilis, Saccharomyces cerevisiae, Bifidobacterium bifidum, Lactobacillus acidophilus and Acinetobacter calcoaceticus, which are not harmful to human health, some of them being commonly found in the human intestine, have been successfully tested for removing alkylsulphates, alkylamines and fatty acids from solutions simulating flotation plant tailings waters. Removals as high as 90% in less than 48 h can be easily achieved with no nutrient requirements, since in most cases the flotation reagent residue to be removed is metabolized by the microorganisms themselves.