Simulation of Landfill Reactors to Understand Hg Release via the Landfill Cover Soil Surface

Landfill is an unignorable emission source of atmospheric mercury (Hg), while the specific source of the released Hg via cover soil surface and Hg migration process remain undefined. Here, landfill simulation reactors were designed to simulate the anaerobic degradation of Hg-containing solid wastes in unsanitary landfills. The characteristics of landfill gas, leachate, and cover soils were investigated to clarify Hg migration and transformation process. Methane, carbon dioxide, oxygen gases, and pH level in leachate suggested that simulated Hg-containing solid wastes underwent the expected anaerobic digestion. During the anaerobic digestion, total Hg concentration in leachates and cover soils from the reactors with Hg addition in solid wastes was far higher than that from the control. Moreover, the total Hg concentration in cover soils increased with time, with even total Hg concentration in the topmost soils reaching 281.27 μg kg−1 on the 212th day. These results indicated that gaseous Hg0 can be generated in the waste layers during the anaerobic decomposition of solid wastes. The gaseous Hg0 could migrate to cover soils through diffusion and advection, while a portion of gaseous Hg0 can be adsorbed by cover soils. Therefore, it is concluded that the released Hg via cover soil surface is from Hg in both cover soils and solid wastes, and diffusion, advection, and adsorption play an important role in the Hg release process. These findings improve the understanding of the landfill Hg emission process and provide positive implications for Hg management in landfills.