Heavy metal immobilization during the codisposal of municipal solid waste bottom ash and wastewater sludges

One of the problems attendant to the incineration of municipal solid waste (MSW) is the siting and design of secure landfills to receive combustion residues from the incineration process. The authors have completed a study for a solid waste cooperative that was interested in codisposing MSW bottom ash and wastewater sludges. This codisposal scheme was initiated to address severe ash disposal problems within the Lamprey Regional Solid Waste Cooperative, and a severe sludge disposal problem in the City of Somersworth, NH, a member of the Cooperative and host city to the proposed codisposal site. The design of the landfill indicated that mixtures of bottom ash and combined sludges would range between 10:1 and 5:1 (by volume). An assessment of the leachate characteristics over time was required to address issues of pretreatment requirements, groundwater monitoring, and the potential sequestration and mobilization of heavy metals from the ash by organic ligands present in the sludge. This paper focuses on the biogeochemical conditions in the ash/sludge matrix that are conductive to the immobilization of heavy metals within the matrix via sulfide or polysulfide precipitation.