Roles of different humin and heavy-metal resistant bacteria from composting on heavy metal removal.

This study aims to assess the roles of different humin and heavy-metal resistant bacterial community from composting on heavy metal removal. The results showed that the concentration of Cu2+, Zn2+, Ni2+, Pb2+, Cr3+ and Cd2+ decreased with adding the compost-derived humin, but the removal rates were relatively low (<30% on average). The heavy metal resistant bacteria from composting have better metal binding capacities than humin, and the combined addition of humin and bacteria could further stimulate the biosorption of heavy metals with 60-80% removal of metals and improve the diversity and biomass of bacterial community. There was obviously increased synergy between the humin from maturity phase and bacteria for metal biosorption ("1 + 1 > 2"). Structural equation modeling showed that microbial biomass and humin humification are the key factors for the biosorption of heavy metals. Combining humin from maturity phase with heavy-metal resistant bacteria was suggested to control heavy metal pollution in composts.