Bioavailability reduction of heavy metals through dual mode anaerobic Co-landfilling of municipal solid waste and industrial organic sludge

Abstract

Heavy metal physiology during landfilling process defines its overall efficacy. In this study, bioavailability of heavy metals (Cu, Pb, Cr, Ni, Cd and Zn) was investigated using Tessier’s sequential extraction method during co-landfilling of pressmud and municipal solid waste performed in dry tomb – bioreactor landfilling as dual mode. Pressmud and municipal solid waste were mixed in three distinct proportions in separate landfill reactors, viz., 1:3, 1:1 and 3:1 against control reactor with sole municipal solid waste disposal. As bioreactor operation, periodic leachate recirculation was performed in all the reactors, after 192 days of dry tomb landfilling. The results revealed that dry tomb – bioreactor landfilling approach of landfilling induced significant reduction in bioavailability of heavy metals. Moreover, addition of pressmud as industrial organic sludge in simulated landfills, further enhanced the immobilization of heavy metals. In particular, landfill reactor with equal co-disposal ratio, achieved highest increments in stable residual fractions (Cr, Ni, Pb, Cu, Cd and Zn by 4.69%, 8.45%, 6.80%, 6.84%, 3.40% and 4.35%, respectively) of each heavy metal after 300 days of dual mode landfilling operation. Other co-disposed landfill reactors also attained significant reductions in bioavailability of heavy metals, unlike control reactor. The variations in species of heavy metals were reliant on co-disposal proportions of pressmud and municipal solid waste. In addition, correlation analysis between physico-chemical parameters and speciation of heavy metals also advocated dependency of landfilling environment on variation of heavy metals and their potential transformation into relatively stable states.