Abstract
Despite the extensive attention paid to the transport of heavy metals in sludge landfills, the processes of transporting these pollutants from a landfill to the underground environment are quite complicated and subject to significant uncertainty. In this study, the transport of typical heavy metal pollutants in a sludge landfill through saturated and unsaturated soil zones during rainfall was investigated via numerical modeling. The objectives of the study are to evaluate the heavy metal pollution risk from a sludge landfill under rainfall infiltration conditions and to propose several management suggestions. The results indicate that, during rainfall, heavy metal concentrations at the top of the unsaturated sludge layer decrease rapidly, but they decrease more gradually at the bottom of the layer. The maximum concentration appears in vertical distribution and decreases gradually through the saturated zone. Nickel is the first heavy metal pollutant to break through the low‐permeability natural silt barrier. The transport parameters not only influence the simulated time for heavy metal pollutants to break through the silt layer and cause underground environmental pollution but also affect the extent to which the heavy metal pollutants in pore water exceed the guidelines. On the basis of these results, for dredged sludge with heavy metal concentrations significantly exceeding the standard, the concentration of heavy metals in pore water should be reduced before the sludge is landfilled, and a covering layer should be established on the sludge surface to control rainfall infiltration.
Highlights
Solidification/stabilization technology is widely used to treat sludge dredged from rivers and lakes before they are transported to landfills [1]
Pollutants in the dredged sludge, such as heavy metals, cannot be removed through solidification/stabilization [2, 3]. ese heavy metal pollutants may migrate to underground environments via mechanisms such as convection, diffusion, dispersion, and adsorption, especially in simple landfills common in China [4, 5]. ese landfills generally do not have either a bottom liner system or a closure cover system, and their antiseepage properties are dependent on the low permeability of natural clay layers [6, 7]
Erefore, the transport parameters influence the time for heavy metal pollutants to break through the lowpermeability natural silt barrier and cause underground environmental pollution. ey affect the extent to which the simulated heavy metal pollutants in pore water exceed the guidelines
Summary
Solidification/stabilization technology is widely used to treat sludge dredged from rivers and lakes before they are transported to landfills [1]. Pollutants in the dredged sludge, such as heavy metals, cannot be removed through solidification/stabilization [2, 3]. Ese heavy metal pollutants may migrate to underground environments via mechanisms such as convection, diffusion, dispersion, and adsorption, especially in simple landfills common in China [4, 5]. Previous studies have proposed a number of methods for modeling pollutant transport in underground environments [7,8,9]. What the laws of heavy metal concentration in unsaturated porous media are and how the pollutions in landfill migrate into the surrounding area, the simulation study on this phenomenon is still a novel issue. The pollution level of landfill for the underground environment is closely related to the site
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