Effects Of Amendments On Humus Formation And Its Electron Transfer Capacity During Silkworm Sand Compost

Composting has become an important way to treat livestock and poultry manure.Humus is an important organic matter produced in the humification process of composting.It could act as an electron shuttle in the environment to promote the reduction of toxic pollutants in the environment.However,the effects of amendments on the formation of humus and its electron transfer ability during livestock manure compost are still unclear.Therefore,in our study,biochar/MnO₂ was added to silkworm sand compost.And samples at different phases of compost were collected to analyze the changes in physicochemical indicators and microbial communities.In order to explore the effects of amendments on humus forming and its electron transfer ability changing.Humus（humic acid,HA,fluvic acid,FA）were extracted in different phases during composting.The concentration,structural and electron transfer ability of humus were analyzed combined with spectroscopy,electrochemical and reduction capacity methods.The addition of biochar slightly inhibited the humification of organic matter during silkworm sand composting,and only promoted the electron transfer ability of the humus.The addition of biochar made the content of humus reduced in each phase of composting.Compared with the control group,the contents of FA and HA decreased by 1.1～20.1%and 4.3～16.6%,respectively,and HA/FA decreased by 4.8～15.9%during the composting process;the humus aromaticity index SUVA254 and SUVA280during the composting process were also lower than the control group.FTIR showed that the addition of biochar had no significant effect on the types of humus functional groups during the composting,but the microbial community was more abundant,which increased the amount of humus in the composting stage.The content of hydroxyl（-OH）and amide group（O=C-NH）were also increased.The addition of biochar promoted the electron receiving capacity of FA increase by 8.9%in the pre-decomposition stage,the nature reduction capacity increased by 12.4%,and the chemical reduction capacity increased by 12.5%.Compared with the control group,the electron accepting capacity of HA in the decomposing stage of the biochar treatment increased by 18.8%,the nature reduction capacity increased by 9.1%,and the chemical reduction capacity increased by 40.2%.Adding MnO₂ can strengthen the humification process of organic matter and improve the electron transfer ability of humus in some stages of silkworm sand composting.The addition of MnO₂ promoted the formation of FA in compost,among which the content of FA in the decomposing stage increased the most,by 31.7%,the content of HA in the high temperature stage increased by 13.7%,and the ratio of HA/FA increased by 23.0%;the SUVA254 and SUVA280 of humus in the decomposing stage were also higher 3.6%and 4.0%than control group,respectively.FTIR showed that the addition of MnO₂ had no significant effect on the types of humus functional groups during the composting,but promoted the content of hydroxyl and amide groups in the humus in 3^rd and 15^th days,at the same time,it is conducive to the increase of microbial community structure in some stages.The electron supply capacity of FA increased by36.2%,and the nature and chemical reduction capacity in the early stage of decomposing increased by 53.1%and 7.5%,respectively.Compared with the control group,in 3^rd day,the electron accepting capacity and chemical reduction capacity of HA were improved by 4.8%and 14.5%.