Comparative characterization of sewage sludge compost and soil: Heavy metal leaching characteristics

The leaching and accumulation of heavy metals are major concerns following the land application of sewage sludge compost (SSC). We comparatively characterized SSC, the reference soil, and the SSC amended soil to investigate their similarities and differences regarding heavy metal leaching behavior and then to evaluate the effect of SSC land application on the leaching behavior of soil. Results showed that organic matter, including both of particulate organic matter (POM) and dissolved organic matter (DOM), were critical factors influencing heavy metal leaching from both of SSC and the soil. When SSC was applied to soil at the application rate of 48 t/ha, the increase of DOM content slightly enhanced heavy metal leaching from the amended soil over the applicable pH domain (6 < pH < 8) and at alkaline pH, and led to more DOM-bound species in the liquid phases. However, the increase of POM content with the SSC application had less influence on the leaching behavior of heavy metals. The geochemical speciation modeling revealed that heavy metal speciation in the solid phase were similar between the reference soil and the amended soil.