Leaching characteristics of the fine fraction from an excavated landfill: physico-chemical characterization

Abstract

This investigation was focused on the physico-chemical characterization of the leachate generated by the fine fraction (<10 mm) of excavated waste from full-scale landfill mining project. The samples were taken in the Kudjape Landfill, Saarema Island, Estonia in four different test pits (TP1, TP2, TP3, TP4) that were divided in four different layers (L1, L2, L3, L4). Total chemical oxygen demand (CODt), dissolved chemical oxygen demand (CODd), total organic carbon (TOC), dissolved organic carbon (DOC) and metals (Zn, Cu, Pb and Cd) were analyzed. The results have shown that most of the COD fraction released into the water (approximately 70%) was in particulate/colloidal state. The TOC released ranged between 3,530- mg/kg dry matters and 2,326 mg/kg dry matter for test pits. Dissolved organic matter (DOC) had concentrations ranging between 365-874 mg/kg and 317-940 mg/kg for different test pits and sampling layers respectively. Very low average leaching rates (%) of metals were observed with leaching ranging between 0.2% and 1.5% which might be explained by the lower solubility of these metals in alkaline pHs. Pb had a significantly higher average leaching rate (1.0%) in comparison to Zn (0.70%) and Cu (0.35%). This study also showed the potential use of CODt as a surrogate indicator of organic carbon in both suspended and dissolved forms (TOC and DOC) and also Zn on the basis of high correlation coefficients observed. To conclude, the proposal and implementation of adequate management strategies that minimize environmental impacts and take advantages of the beneficial use of fine-grained fractions in landfill mining rely on detailed physico-chemical characterization of both the fine fractions itself and the leachate generated during storage and use.