The impacts of metal ions on phytotoxicity mediate by microbial community during municipal solid waste composting

Metal ions (MIs) are the main sources of phytotoxicity of compost product, which can be absorbed by plants, thereby reducing the germination rate. The aim of this study was to analyze the interactional mechanism among MIs, microbial community, the structure of water soluble organic matter and phytotoxicity during composting. The results indicated that phytotoxicity was positively correlated with MIs (II) (As, Cd, Hg, Cr, Fe, Mn and Pb), and negatively correlated with MIs (I) (Mg, Zn, Ni and Cu). Furthermore, SO₄^2-, organic matter (OM), pH and four bacterial species significantly influenced the association of MIs to phytotoxicity. Additionally, molecular weight, protein-like substance and oxygen-containing functional groups relating to MIs (II) were significantly influenced by the nine bacterial species. Based on the response of physicochemical parameters on these key bacterial species, three possible mutual mechanisms were proposed using the structural equation model. Accordingly, a regulating method was proposed to reduce the phytotoxicity during composting.