In situ immobilization of the selected heavy metals by sulfide compounds in landfills under methanogenetic conditons

Abstract

Co-disposal is a technique for the controlled disposal of hazardous wastes together with municipal solid waste. Co-disposal of industrial wastes including heavy metals and disposal of household hazardous substances such as batteries, paints, dyes and inks -in paper result in release of heavy metals into a landfill environment. Zinc, iron, nickel, copper and cadmium are the most common heavy metals disposed to landfills. These metals are controlled by several attenuation mechanisms including adsorption, acid-base, oxidation-reduction and precipitation-complexation reactions. This research aimed to better understand the extent of heavy metal attenuation in landfills by means of precipitation by sulfide compounds. The effect of selected heavy metals (Zn, Cu, Cd, Fe, Ni) on solid waste stabilization together with the effect of leachate recirculation on the attenuation mechanisms was also investigated. For this purpose, two landfill simulating reactors were used in the laboratory. These reactors were constructed and filled with shredded and compacted municipal solid waste having typical solid waste composition determined for istanbul region. Two reactors, one with leachate recirculation, the other without were operated in the constant temperature room of 32°C to enhance the growth of anaerobic microorganisms. Moreover, moisture addition was done into the reactors in order to simulate the annual rainfall. After the onset of the methanogenetic conditions in both reactors, the selected heavy metals including iron, copper, nickel, cadmium and zinc were added into the simulated landfill reactors. The metals (Fe, Cu, Ni, Cd, Zn ) were prepared by dissolving the metal salts in one liter deionized water and introduced into the bioreactors according to the amounts suggested for co-disposal under the directives of the Turkish Hazardous Waste Control Regulations to prevent inhibition of the microbially mediated processes during waste stabilization This research indicated that when sulfide concentration was very low or insufficient, the removal of the metals was controlled by other anions such as C03 = and P04- 3 until the reduction of sulfate coming from loaded metal salts into the reactors Moreover, leachate recirculation offers opportunities for more rapid waste stabilization including attenuation of co-disposed heavy metals.