Study On The Changes Of Dissolved Organic Matter And Heavy Metals In Compost

In recent years,with the rapid development of livestock and poultry breeding industry in China,the emission of livestock and poultry manure is increasing rapidly.Composting technology reduces the harm of livestock and poultry manure to the environment to a large extent by reducing,harmless and resource-based.However,due to the addition of a large number of trace elements in livestock and poultry breeding,the content of heavy metals in compost products is high,which has a certain impact on the quality of soil and agricultural products after the compost products are applied into the farmland soil.Dissolved organic matter(DOM),as the most active part of composting organic matter,can reflect the structural evolution of organic matter in the composting process,and the composition and structure of DOM are complex.In the composting process,the degree of molecular polymerization,aromatization and humification will occur,thus affecting the content of heavy metals.In this paper,pig manure,cow manure and chicken manure from a large-scale farm in Hefei suburb were used as research objects.DOM was extracted from compost samples at different stages in the composting process by indoor simulation composting method.DOM was divided into five components by leenheer improvement method: hydrophobic acid component(HOA),hydrophobic neutral component(HON),hydrophobic basic component(HOB),hydrophilic component(HIM)and acid insoluble component(AIM),the composition and change of different components of compost DOM were studied by means of element analysis and UV spectrum.The transformation rule of DOM was analyzed by means of element composition,molecular structure and functional group,so as to better reveal the mechanism of DOM and heavy metal.The main results are as follows:(1)After 70 days of composting,the content of DOM in the three composts increased;with the composting,the content of hydrophobic component(HOA,HOB,HON)and acid insoluble component aim increased,while the content of hydrophilic component HIM decreased.After composting,the relative content of hydrophobic material in the three composts increased,while the relative content of hydrophilic material decreased The hydrophobicity of DOM is enhanced.With the development of composting,the content(mass fraction)of HOA in three kinds of composting decreased first and then increased.At the end of composting,the content of HOA was the highest.Because HOA can be regarded as fulvic acid and humic acid,the increase of HOA in composting process showed the increasing of humus.(2)The changes of element composition of three compost DOM are different: cow manure composting process DOM The content of C and C / N decreased,the content of N element was stable,the content of H and O increased first and then decreased;the content of DOM C decreased,the content of N element decreased first and then increased,the content of H and O element increased slightly in the early stage,and decreased in the later stage;the content of DOM in chicken manure compost The content of C element decreased,the content of N decreased more than that of cow manure and pig manure.The content of H element decreased as a whole,and the content of O increased first and then decreased.(3)Through the analysis of UV-Vis spectrum,it was found that: suva254 and suva280 of different compost DOM and components increased with the composting process,indicating that the degree of humification,aromaticity and molecular weight of compost DOM and components increased in different degrees,and the non humus substances in cow manure,pig manure,chicken manure DOM and its components gradually transformed into humus substances after 70 days of composting The correlation analysis results of E465 / E665 and E253 / E203 showed that the five components reached the state of maturity with the composting,among which AIN had the highest maturity,HOA was slightly lower and HIM was the lowest.(4)In the process of composting,the contents of heavy metals in DOM and its components of cow manure,pig manure and chicken manure were different.As a whole,the content of Zn in DOM,HOA,HOB,HON,AIM and other components of three composts is the highest,and the content of Cu and Fe is in the middle,which changes with the composting time,while the content of As and Cd is the lowest,and the content of As and Cd almost has no obvious change in the composting process;Compared with the content of Cu,Zn and Fe in DOM and components of three composts,the content of Cu,Zn and Fe in DOM and components of pig manure is higher.It is higher than cow manure,chicken manure DOM and other components in the ability of coordination and binding of heavy metals.Among the five components of compost DOM,Cu,Zn,Fe are enriched in HOA,AIM and HIM in different degrees,and the increase of HOA and AIM content with the compost also leads to the enrichment of heavy metals in the compost.