CHARACTERIZATION AND LEACHING OF ELEMENTS FROM MUNICIPAL SOLID-WASTE COMPOST

Municipal solid waste (MSW) compost was collected from the St. Cloud, MN and Pembroke Pines, FL composting facilities on several occasions during 1990 to 1993. The total content, phase association, and water solubility of cadmium (Cd), lead (Pb), iron (Fe), copper (Cu), chromium (Cr), nickel (Ni), and zinc (Zn) were determined using sequential chemical extraction (SCE) and synthetic acid rainwater cascade (SRC) extraction protocols to assess the environmental acceptability of MSW composts. The MSW composts are enriched with Pb (314-671 mg/kg), Cd (2.6-10.8 mg/kg), Cu (121-762 mg/kg), and Zn (540-2790 mg/kg). The SRC leachable fraction of Cu, Zn, Cd, Cr, Pb, and Fe was <6% in the Pembroke Pines compost and <10% in the St. Cloud compost. Nickel solubility, however, was high and variable in the composts studied. The SRC-extractable Ni ranged from 11.3% for Pembroke Pines compost to 56.2% for St. Cloud compost. The SCE-exchangeable fraction of Cu, Cr, Ni, Zn, and Fe in these composts was <4%. Cadmium was an exception, where 12.8 and 10.3% of the Cd was extracted from the SCE-exchangeable phase of the St. Cloud and Pembroke Pines composts, respectively. Higher Cd contents of the SCE-exchangeable phase extractions in comparison to the SAR leachates for these composts is attributed to the formation of soluble Cd complexes because of the use of MgCl2 as the SCE exchangable phase extraction fluid.