Leaching characteristics of heavy metals in MSW and bottom ash co-disposal landfills

Bottom ash (BA) management is often implemented through its co-disposal with municipal solid waste (MSW) in landfills. However, BA co-disposal may lead to heavy metal leaching in landfills. In this study, the effect of BA co-disposal on heavy metal leaching behavior under different scenarios, specifically, MSW, low BA co-disposal (BA_L), high BA co-disposal (BA_H), and BA monofill were investigated. The heavy metal concentrations in the leachate decreased in landfills over time. The leached metals primarily included Zn, Cu, Mn, Pb, Cr, and Cd. The discharge concentration ratio of heavy metals in the leachates exhibited the following decreasing order: MSW, BA_L, BA_H, and BA. In particular, the discharge concentration ratio of Cu in the MSW, BA_L, BA_H, and BA cases ranged from 7.1 × 10^-3 to 8.8 × 10^-1 (mean = 3.0 ×10^-1), 2.8 × 10^-4 to 2.0 × 10^-1 (mean = 5.4 ×10^-2), 9.1 × 10^-5 to 3.0 × 10^-2 (mean = 5.9 ×10^-3), and 4.4 × 10^-4 to 7.9 × 10^-3 (mean = 1.8 ×10^-3), respectively. Moreover, the leaching of the heavy metals could be attributed to waste contents, properties of the heavy metals, and leachate characteristics, such as the pH, chemical oxygen demand (COD), alkalinity, and Cl^- content. The presented findings can help clarify the leaching characteristics of heavy metals in BA co-disposal landfills, thereby facilitating the optimization of practical landfills.