Electron Transfer Mechanism Of Organic Matter In Composting Of Different Materials

Humic acid(HA),an important product in the composting process,is formed by the conversion of organic matter through a series of sequential biochemical processes.Under anaerobic conditions,HA can obtain electrons from microorganisms acting as an electron acceptor.Meanwhile,it can also become an electron donor and deliver electrons to the terminal acceptor.Dissolved organic matter(DOM)is the most active part of compost organic matter.It has complex structure and component that includes dissolved HA and other organic matter,which leads to the redox capability of DOM.While,these two types of compost organic matter have both similarities and differences in structure and component.This study investigates the effects of structural and component changes of DOM and HA on the electron transfer ability of different material composts by collecting different stage of municipal sludge compost and swine manure compost samples.Then,different types of compost organic matter was extracted,which was followed by the characterization of the change of the compost organic matter's chemical component and structure by the method of spectroscopy.Finally,analyzing the electronic transfer capacity(ETC)(including Electroaccepting capacity(EAC)and the electron donating capacity(EDC))of compost organic matter in combination with electrochemical methods.The EDC,EAC,and ETC of municipal sludge compost HA showed overall increase.During the early period of composting,there are many small molecules in the organic matter,and protein-like substances included,which are the main components of humus.Therefore,the compost has low humification degree and low aromaticity.With the progress of composting,protein-like substances are gradually degraded or converted into humus-like substances,and their molecular weight,aromaticity,and compost humification degree all increase.These changes make the content of quinone groups in HA increase,while the quinone groups is the main contributing functional group of the electron transfer ability of organic matter.Therefore,the ETC of HA in the late stage of composting is enhanced.The structural changes of DOM during swine manure composting are similar to those of HA.With composting process,the relative content of protein-like substances in the DOM decreases,while the relative content of humus-like substances increases,which leads to the increase of compost stabilization.The ETC of DOM also increases.Infrared spectroscopy showed that the functional groups such as hydroxyl and carboxyl groups of DOM did not contribute significantly to ETC during composting.Elemental analysis results indicate that sulfur-containing groups in DOM contribute to the increase of ETC.Swine manure as a compost material has a higher protein content than municipal sludge.However,the composition and structure changes of the two components are similar in the composting process.Both of them change with a decrease in protein-like components,an increase in humus-like components,the molecular weight of organic matter and sexuality,all of those showed the similar change trend of ETC of compost organic matter.However,there are significant differences in the ETC values of different extraction types of organic matter,in which the ETC of DOM is smaller than that of HA.This study explores the effects of organic matter component and structural changes on different compost materials,which provides a scientific basis for further evaluation of compost organic matter ETC for the degradation of pollutants,the safe use of compost products and the good environmental effects with the utilization of compost products.