[Influence of organic matter evolution during composting on the bioavailability of heavy metals]

Ion chromatography, fluorescence spectroscopy, UV-visible absorption spectroscopy and multivariate statistical analysis were applied to study the composition and evolution characteristics of dissolved organic matter (DOM) and heavy metal extracted from chicken manure during composting, and the influence of organic matter evolution on the bioavailability of these heavy metals was further investigated. The result showed that, a large number of organic acids were generated during the active stage, and their concentrations were in the range of 2097.55-2155.61 mg x L(-1), 39.24-51.58 mg x L(-1), 12.52-12.90 mg x L(-1) and 1.68-2.31 mg x L(-1), respectively. During the curing stage, protein-like matter was degraded, whereas humic-like substances were formed, which increased the humification degree, condensation degree and stability of DOM. The content (1.069-7.106 mg x L(-1)) of dissolved iron ranked first during composting, that of dissolved Al, As, Cr, Cu and Mn (0.1-1.008 mg x L(-1)) ranked second, and the concentration of dissolved lead was the lowest. Concentrations of all heavy metals decreased during composting except aluminum. Furthermore, the result from correlation analysis showed that these dissolved heavy metals were bound with DOM, and their bioavailability was low. It could be concluded that, the bioavailability of the heavy metals in chicken manures became lower through the decrease of dissolved heavy metals and the binding between dissolved heavy metals and humic-like substances.