The effect of reagent nature on detoxification of aerobically stabilized sludge of biological treatment plants from heavy metals
I.V. Zykova, V.A. Isakov
Section: Ecologization of industry
One of the methods of detoxification of aerobically stabilized sludge of biological treatment plants from heavy metals is a chemical method based on shifting the equilibrium of reversible metal binding processes by compounds of aerobically stabilized sludge with the introduction of poorly soluble calcium compounds. It was found that about 35% of copper(II), lead(II), cobalt(II), and nickel(II) interact with organic substances that make up the aerobically stabilized sludge by the complexation mechanism, 25% are co-precipitate on Fe2O3, MnO2, CaCO3, MgCO3, and about 25% is co-precipitated by the mechanism of isomorphic substitution on silicates and aluminosilicates. About 55% of chromium(III) is co-precipitated with Fe2O3, MnO2, CaCO3, MgCO3 by adsorption and occlusion mechanisms, about 28% is co-precipitated with silicates and aluminosilicates by isomorphous substitution mechanism, and about 8% is bound with organic substances by the complexation mechanism. The maximum recovery of metals from aerobically stabilized sludge (50–65%) is achieved by using poorly soluble calcium compounds in doses of 25 g/dm3. At introduction of insufficiently soluble calcium compounds the metals bound to compounds of aerobically stabilized sludge by mechanisms of physical and ion exchange adsorption are extracted, a significant proportion of metals co-precipitated with iron(III) and manganese(IV) oxides, with calcium and magnesium carbonates by the mechanisms of adsorption and occlusion, and bound to organic compounds by complexation mechanism. Metals forming chelated complexes with aromatic compounds and metals coprecipitated on silicates and aluminosilicates by the mechanism of isomorphic substitution are not extracted in contact with the injected materials, regardless of their nature. After detoxification of the sludge, the indicators for copper, lead, nickel and chromium (mg/kg of dry matter) do not exceed the established standards for sludge (GOST R 54534-2011 and GOST R 54651-2011), allowed for use as fertilizers and soils for biological remediation of disturbed lands.
ISSN 1995-4301
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