Heavy metals speciation study revealing merits of anaerobic co-disposal of municipal solid waste with discrete paper mill sludges: An experimental investigation in simulated landfill bioreactors

Abstract

Speciation of heavy metals (Cu, Cr, Pb, Ni, Cd and Zn) during anaerobic co-disposal of two distinct paper mill sludges viz. effluent treatment plant sludge and de-inking plant sludge with municipal solid waste in anaerobic landfill bioreactor was investigated. Effects of moisture content, volatile solids and pH on fractionation of heavy metals over the course of landfilling were also analyzed. Study revealed enhancement in bioavailability of Cu, Cr, Ni and Cd on sole disposal municipal solid waste in bioreactor landfill over 300 days. However, co-disposal of effluent treatment plant sludge with municipal solid waste showed reduction in bioavailability of every analyzed heavy metals with maximum increment in stable residual forms of Cu, Cr, Pb, Ni and Zn by 3.70 %, 0.73 %, 3.08 %, 1.17 % and 3.45 % (dry weight), respectively. De-inking sludge co-disposal was also found effective for reducing bioavailability of Cu, Cd and Zn while bioavailability of Cr, Ni and Pb was unaltered. Strong correlations between increase in residual forms of heavy metals and volatile solid reduction obtained for both co-disposed bioreactors.