Mass balance of heavy metals in a non-operational incinerator residue landfill site in Japan

To better understand the general behavior of heavy metals in semi-aerobic incinerator residue landfills, we developed a general equation for calculating the mass balance of heavy metals (cadmium, lead, copper, zinc, mercury, and chromium) based on monitoring data from incineration plants and landfill sites. The mass balance results showed that 0.0042%, 0.001%, 0.0004%, 0.0019%, 0.022%, and 0.0065% of the disposed Cd, Pb, Cu, Zn, Hg, and Cr, respectively, were washed out by rainfall from 1975 to 2015. Heavy metals (Cd, Cr, and Hg) with a lower total mass in the landfill had a relatively high total leaching rate. This may be because of the high pH of the landfill, which affected the leaching of Pb, Zn, and Cu. According to our analysis of the changes in annual leaching rates at this landfill site, there was an obvious change in those of Cu, Zn, and Pb after 1989, when the pH of the leachate increased suddenly. The overall annual leaching rate became more stable, at around 0.00002%, following closure of the landfill site, and it is believed that the dissolvable fraction and heavy metal concentration in the leachate are expected to reach a limit under the current conditions.