Influence of dissolved organic matter and heavy metals on the utilization of soil-like material mined from different types of MSW landfills

Soil-like material (SLM) mined from municipal solid waste (MSW) landfills can be used as nursery cultivation soil, landfill cover, and as a building material. However, SLM utilization is restrained by heavy metal (HM) contents whose speciation and migration are influenced by their dissolved organic matter (DOM) content. Therefore, the properties of aged refuse and the correlation between DOM and HM forms were studied using samples from different types of MSW landfills. The dominant components of aged refuse were SLM (18.80%-83.51%) and plastics (11.17%-65.51%). The moisture, organic matter, and pH ranged from 29.55% to 57.92%, 15.70%-57.68%, and 7.84-8.51, respectively. The Zn content was highest (455.48-1379.27 mg/kg) in the SLM, followed by Cu (96.29-428.90 mg/kg), Cr (49.10-236.21 mg/kg), Pb (53.52-222.71 mg/kg), and Ni (20.92-39.10 mg/kg). The SLM cannot be used for agriculture because the HM contamination exceeds the multiple of 0.07-7.99. Zinc in the acid-soluble state and reducible state had the highest mobility in SLM. However, Cu and Pb, mainly in the oxidizable state, and Cr and Ni, in the oxidizable and residual states, were relatively stable. In the sanitary and simple MSW landfills, the average proportion of protein-like materials decreased from 84.44% to 82.61% and from 65.58% to 55.94%, respectively, as the landfill depth increased. Both the acid-soluble and oxidizable HM states and all forms of Zn in the SLM were significantly positively correlated with tyrosine-like materials (r = 0.58*-0.87**). Protein-like materials may enhance the mobility of HMs.