Effects of landfill refuse on the reductive dechlorination of pentachlorophenol and speciation transformation of heavy metals

Landfill refuse is a mixture of inorganic minerals and organic matter that is capable of undergoing complexation and redox reactions due to its active functional groups. Organic matter often combines with minerals in landfill refuse and it remains unclear whether this combination involves electron transfer. Therefore, the effects of landfill refuse composition on reductive dechlorination and speciation transformation of heavy metals were investigated in this study. Results show that landfill refuse comprises protein- and humic-like substances, aliphatic structures, and a large number of hydroxyl, carboxyl, quinoid and other active functional group. The electron donating capacity (0.09-0.26 mu mol/g(C)) of landfill refuse was found to be higher than its electron accepting capacity (0.03-0.23 mu mol/g(C)), indicating that electron donating groups (hydroxyl) were the main redox-active moieties, facilitating the reductive dechlorination of pentachlorophenol (PCP) by microorganism. Fe2O3, FeO and SiO2 were the main inorganic minerals affecting PCP dechlorination. The speciation distribution of heavy metals in landfill refuse was determined by the BCR sequential extraction method. Results showed that Zn and Ni have high potential migration capacity, poor stability and the highest bioavailability, while Cr, Cu and Pb are relatively stable and have weak migration potential. The oxygen- and nitrogen-containing functional groups, aliphatic structures and aromatic carbon in landfill refuse can promote the transformation of Ni and Cr from an unstable to stable state. Protein-like substances exhibit a strong Cu binding ability, allowing Cu to combine with organic matter more easily than other assessed heavy metals. Both Fe2O3 and FeO affected the stability of Cu. FeO promoted the stabilization of Zn, whereas Fe2O3 and SiO2 promoted Cu instability. These results could provide some references for the treatment of organic chlorides and the stabilization of heavy metals in landfill refuse in China. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The study found that landfill refuse contains a variety of active functional groups, with electron donating capacity higher than electron accepting capacity, mainly achieved through hydroxyl groups; Inorganic minerals and speciation distribution of heavy metals in the refuse were affected, with zinc and nickel showing high migration potential, while chromium, copper, and lead are relatively stable.