Investigation Into The Formation Of Humic Substance And The Mechanism Of Heavy Metal Variation After Vermicomposting Of Pig Manure

In this paper, a mixture of pig manure and 13 C rice straw was vermicomposted with Eisenia fetida for 40 days. The contents of study included the basic properties of substrate and heavy metal variation before and after vermicomposting, the variation of dissolved organic matter(DOM) and humic substances and their heavy metal among them, the impact factors of the Humic acids(HA) from vermicomposting complexed with Cu, and the effect of earthworm activity on the change of humus and its heavy meta were investigated. All the results were as followes:(1) During the progress of vermicomposting, the survival rate and quality of earthworms were similar, they both reduced at first then increased at the end. After composting, earthworm treatment made the pH, EC, temperature and CEC of substrates increased; the content of TC, TN increased while the C/N decreased; and the total P, total K and the available N, P, K also increased; and the microbial biomass carbon was reduced but the catalase was increased. The earthworm could accumulated the heavy metals Cu and Zn, and the enrichment capability was Cu >Zn。Vermicomposting could raise the total Cu content of substrates and decrease the available Cu content, but the Zn had the opposite change. On the basis of the δ13C values, there was a correlation of the migration behavior of 13 C rice straw and heavy metal in the earthworm and intestinal vermicompost, and a relation between the Cu and Zn.(2) After vermicomposting, the content of DOM was increased while the Cu and Zn content of DOM were reduced. The results showed earthworm treatment made the C, H and N content of DOM increase while the O rendue. Compared with natural treatment, earthworm treatment made DOM had more Aliphatic functional groups and Polysaccharide substance, but less the Oxygen-containing functional groups and Nitrogenous substances content; the DOM also had bigger molecular weight and more compolex aromatic structures. Moreover, there were dominance correlations between the δ13C values and content of DOM, but the C source form rice straw was hard to transform the DOM.(3) During the progress of vermicomposting, the HS, HA and FA obstained form substrates were increasing. Compared with nautral composting, vermicompostiong lead to the reduce of Oxygen-containing functional groups, Aliphatic functional groups, Nitrogenous substances and Polysaccharide substances content, and the molecular weight also was desearsed. On the contrary, the Nitrogenous substances and Aliphatic functional groups of FA were increased, but the Oxygen-containing functional groups was reduced. FA had more Polysaccharide substances and aromatic substances or/and Carboxylic acids, and its molecular weight was bigger. Fluorescence spectroscopy showed as the result of vermicomposting, HA and FA had less aromatic protein substances, humic acid-like substances, fulvic acid-like substances and protein-like substances, but they had higher degree of structural complexity. During the earthworm treatment, the variation of δ13C values of HA and FA was opposite, and the δ13C values was FA >HA suggesting the HA might be degraded into FA.(4) All the pH, temperature and the concentration of HA could influence the absorbtion capacity of HA for Cu. On the basis of the Henry equation, Langmuir equation and Freundlich equation, it showed that with the increase of the pH, the adsorption capacity of HA complexed with Cu was increased; the right temperature or HA concentration could make the adsorption capacity greatly. In addition, the fluorescence quenching was observed after the HA complexed with Cu. When the higher the pH, the weaker the peak intensity of fluorescence peak. Similar phenonment was also found the change of HA concentration. With the increase of temperature, the peak intensity was increased at first then reduced at the end. Moreover, the fluorescence of HA obtained form natural treatment was stronger significantly quenched by Cu than that of earthworm treatment,.(5) Earthwrom activity could increase the mineralization rate of humic materials and degradation of organic matter as a result of the reduce of the content of HA and the increase of HS and FA, the ratio of HA/FA was reduced suggesting earthworm treatment increase the content of FA formed from HA; Cu inhibited the earthwrom activity but it lead to the decrease of HS, HA and FA suggesting the complexation reaction of Cu with humic substance. FTIR and fluorescence spectroscopy analysis showed vermicomposting helped the increase of Polysaccharide substances of HA while the reduce the content of Aliphatic substances of FA. Compared with natural treatment, earthworm activity made the increase of humic acid-like substances of HA and the fulvic acid-like substances of FAslowly, and caused the the reduce the content of aromatic protein substances slowly. Moreover, earthworm could accumulated Cu and the capacity of bond Cu was FA > HA.