Electron Transfer Regularity Of Humus From MSW Landfill

Landfilling was defined as the biological decomposition of organic matter to form abundant of mineralized refuse,containing stable humus-like end product.Humus-like substances could serve as redox buffer,and it accepts electrons from microbial respiration and donates electrons to heavy metal and Chlorine,nitrobenzene organic matters,nevertheless,the evolution characteristic and influencing mechanism of electron transfer capacity（ETC）has been seldom reported.To solve this sicence problem,different components of humus were exreacted from the municipal solid waste（MSW）at different landfill depth.We investigated the evolutionary characteristic of the ETC using the chemical,microorganism and electrochemical methods during landfilling.In combination with the modern spectroscopy technology and chemometrics analysis,we explored the evolutionary properties of the humus internal structure,and the relationship between the structure and ETC.In the meantime,further analysis revealed the effect of external conditions,i.e.,pH,ionic strength,dissolved state and mineral adsorption on the humus ETC.Our findings could widen the understanding of the degradation of the organic matters and the transformation of the heaval metals and provide the fundamental and scientific basis for optimizing control the landfill.The typical conclusions are showed below:1.The reducing and oxidating capacity of all components of humus revealed different ETC,electron accept capacity（EAC）and electron donate capacity（EDC）,measured by tradition chemical and electrochemical methods.The microbial reduction capacity was obvious stronger than the native reduction capacity based on tradition chemical experiments.The native reduction capacity and microbial reduction capacity of dissolved and undissolved humus were in the range of 43.60¹65.88μmol·g（C）^-1,158.38¹136.03μmol·g（C）^-1 and 0.37³4.47μmol·g（C）^-1,27.13⁴2.15μmol·g（C）^-1,respectively.The EAC and EDC of dissolved and undissolved humus were in the range of 353.67²097.11μmol·g（C）^-1,499.05¹068.67μmol·g（C）^-1 and 0.03⁰.51μmol·g（C）^-1,0.09⁰.66μmol·g（C）^-1,respectively.The ETC of humic acid（HA）increased significantly with the depth increasing.The ETC of fulvic acid（FA）,humin and humus soil did not show clear trend during landfilling.The donating-electron functional groups of HA after demineralization and FA extracted from shallow layer played an important role,while the accepting-electron functional groups of HA after demineralization and FA extracted from deep layer played a leading role.The donating-electron functional groups of HA without demineralization,humin and humus soil played a significant role.2.The organic matters such as protein of humus degraded,the degradation product such as amino acid can be bond in the refractory lignin and to form macromolecule aromatic humus during landfilling.Thus,the degree of the aromaticity,molecular weight（MW）and hydrophilicity of humus increased gradually.The organic fractions with the high degree of MW,the more relative content of hydroxyl and less relative content of carbohydrate were mainly responsible for the EDC,whereas the organic substances with the high degree of MW and aromaticity,the more relative content of carboxyl and less relative content of carbohydrate accounted for the EAC during composting.3.The conditions of microenvironment affected the electron transfer ability of humus significantly.The increment of the pH was benefit of the ETC of humus.To high or too low ionic strength was bad for the ETC of humus.The ETC of humus was the highest,in the condition of c（KCl）=0.2 M.Afer demineralization and dissolution,the humus exposed more redox-active functional groups and enhanced the oxidation-reduction ability and ETC.