The Evolution Of Electron Transfer Capability Of Humic Substances Extracted From Municipal Solid Waste During Compost And Its Influence Factors

Humic substances which are provided with electron transfer capability, could accept from electron donor and then passe electrons to the electron acceptor. This feature of humic substances could promote the conversion of heavy metals and the degradation of organic matter in nature. In this study, humic substances, which were extracted from different times of compost, were purified into HA, FA and Hyl. The electron donating capacity and electron shuttle capacity of humic substances were measured by Fe(Ⅲ) reduction method to study their evolution during composting. The structure of humic substances was characterized by spectroscopic methods to identify influence factors of electron transfer capability of humic substances.The results showed that, there are differences in electron donor capability between HA, FA and HyI. The electron donor capability of HA and HyI show a downward trend after the first rise while FA shows a downward trend. The electron donor capability of HA is influenced by its structural and components, like degree of C polymerization, aromatic, compost maturity, molecular weight, content of quinone groups and carbon chain structure; The electron donor capability of FA is proportional to the molecular weight while it is negatively correlated with the content of protein-liked components; The electron donor capability of HyI is proportional to the content of quinone group and the proportion of humic-acid-liked components.Like other natural humic substances, humic substances extracked from composting have electron shuttle capability. The amount of electron transferred by the way of humic substances mediated is higher than microorganism. The electron shuttle capability humic substances extracked from composting is affected by many factors, such as electron donor, electron acceptor and humic substances structure.The result which is different from natural humic substances also shows that electron shuttle capability of humic substances from composting is lower than its electron donor capability.Compared with other natural humic substances, the structure of humic substances from composting is simple and unstable. In the process of electron transfer, humic substances could promote microbial reduction of heavy metals as an electron shuttler and be consumed by microbe as nutrient source.This study characterizes the electron transfer capability of humic substances from composting and analyzes its influence factors. The results provide the theoretical basis for definiting the role of humic substances in biogeochemical. The results provide scientific basis for safe use of compost products and repairing heavy metal contaminated soils with compost products.