Impact of compost methods on humification and heavy metal passivation during chicken manure composting

Livestock manure is one of the main sources of heavy metals (HMs) in agricultural soil. So, it is necessary to reduce its bioavailability before used as organic fertilizer. In this study, the passivation effect of HMs and the evolution of dissolved organic matter (DOM) during four composting processes were explored. Results showed that different composting methods had a great effect on HMs passivation rate and humification degree. HMs were released during the thermophilic phase, and were bound by resynthesized humus during the cooling period. The best passivation effect of HMs was found in FV + T treatment, the passivation rate of Cu, Zn, Cd and Pb reached 63.80%, 34.07%, 86.54% and 45.14%, respectively, then followed by the treatment of NV + T and SC. UV-Vis spectra and excitation-emission matrix (EEM) spectra indicated that humus precursors were produced during thermophilic phase and the accumulation of humus mainly occurred in cooling period. This study can be used as a theoretical support for the safe utilization livestock manure.