Investigation Into DOM Changes And Its Regulation Of Heavy Metal Migration After Vermicomposting Of Pig Manure

Due to abuse of feed additive, heavy metal pollution in animal manure is very common, especially copper and zinc pollution.In this paper, pig manure polluted with heavy metals was vermicomposted by Eisenia fetida, and the earthworm growth, composting material changes, changes of heavy metal content, DOM characteristics, the target heavy metals(Cu,Zn) conjunction with DOM and desorption characteristics of heavy metals with DOM and low molecular weight organic acids were investigated. The results were as followed(1)Addition of sawdust was more conducive to the surviving and reproducing of earthworms compared with that of straw. In this study, earthworms had a certain enrichment capacity of heavy metals, and the accumulation of Cu was54.35mg/kg, while the accumulation of Zn up to404.88mg/kg.Vermicomposting could raise the temperature, conductivity of composting materials, with pH reduced. Earthworm could accumulate heavy metals up to a certain point in the pig manure, and heavy metal and available heavy metal content per unit mass of pig manure increased after earthworm treatment. As available heavy metal content increasing, the bioavailability of heavy metals increased.,with increasing risk of heavy metals migration to the environment. Earthworm treatment can effectively reduce the content of the DOM, but compared with the control treatment, earthworms treatment increased the content of heavy metals in the DOM.(2)After earthworm treatment, the molecular weight of DOM decreased in general, and its distribution range became larger. Compared with the control treatment, earthworm treatment made the presence of large molecular weight substances in the DOM. Elemental analysis showed that O, N structure of the DOM increased, while the structure containing C decreasing. FTIR, UV spectra, E4/E6value showed that earthworm treatment made smaller molecular weight of the DOM as a whole,while the content of aromatic compounds and soluble humus increasing.(3)Fluorescence spectra of DOM unraveled that humic acid content was reduced while the fulvic acid content showed reverse behavior. The analysis of fluorescence spectrum in terms of DOM complexed with Cu(Ⅱ) revealed the effect that fluorescence quenching of Cu(Ⅱ) on DOM was remarkable, and DOM from vermicompost was more likely to complex with Cu(Ⅱ) and could lead to a shortening of its straight chain or the pyrolysis of aromatic group. Groups such as-OH and-NH2in DOM engaged in the complexation with Cu(Ⅱ). Moreover, fulvic acid in DOM after vermicomposting was more conducive to the complexation with Cu(Ⅱ). Zn(Ⅱ) could enable the fluorescence intensity of each treatment to strengthen.(4)DOM had the best heavy metals desorption from pig manure after earthworm treatment. Citric acid and malic acid had the strongest desorption over heavy metals from pig manure. Within a certain range. the content of heavy metals desorpted from pig manure increasesed with the concentration of organic acids increasesed, pH value decreased, The study found that the desorption time of4h, the temperature20～3C℃, were the most conducive to the desorption of heavy metals in the pig manure. By comparison, the content of Zn desorped from pig manure was greater than that of Cu. Heavy metals in the pig manure after earthworm treatment are more likely to be desorpted by low mocular organic acid. A further indication, the earthworm treatment could lead to heavy metals in the oig manure through the DOM migration to the environment...