Study On The Effect Of Wheat Biochar On The Humification And Electron Transfer Of Sludge Aerobic Composting

In recent years,the output of municipal sludge as a by-product of urban drainage treatment has been increasing with the increase in sewage volume.Disposal of it at will will cause environmental problems such as land pollution.Composting is an effective way to turn sludge into resources.As an additive,biochar can provide carbon source for aerobic composting of sludge,reduce nitrogen loss,and accelerate the composting process.Under certain conditions,the humus produced by composting can act as an electron acceptor to get electrons from microorganisms,and then transform into an electron donor to transfer electrons to the terminal acceptor.It has great potential in the treatment of heavy metals and organic pollutants.In this study,0%,5%,and 10%biochar were added to the sludge aerobic composting,and the samples at different stages of the composting were collected and separated into humic acid,fulvic acid and hydrophilic components,and the physical and chemical indicators were measured,Spectroscopy and electrochemical methods to study the effect of biochar on the humification and electron transfer capacity（ETC）of sludge aerobic composting.The main research conclusions are as follows:（1）The results of physical and chemical properties reflect that the addition of biochar promotes the aerobic composting effect of sludge.The duration of high temperature in the 5%and 10%biochar groups was extended by 1 day and 2 days respectively,the carbon-to-nitrogen ratio（C/N）and volatile organic matter（VS）decreased more than the control group,and the seed germination indexes were both before and after composting.Higher than the control group.There was no significant difference in the p H value,water content and conductivity of each treatment group.（2）Adding biochar can deepen the humification of sludge aerobic composting.Through the UV-vis spectrum and the change trend of characteristic parameters such as SUVA₂₅₄,SUVA₂₈₀,SUVA₄₃₆,A_226-400,it can be seen that the C bond content,molecular weight and quinone content of composting humus after adding biochar were higher than those of the control group at the ripening stage,and reached the humization peak in advance.This result was also confirmed by three-dimensional fluorescence spectrum,Humicification Coefficient（HIX）Index and parallel factor analysis.Fourier transform infrared spectroscopy shows that alcohols and phenols in composting are decreasing as microbial carbon sources,and aromatic compounds and carboxyl groups are synthesized and consumed in the process of composting.（3）The addition of biochar improves the electron transfer ability of humus in sludge aerobic composting,and the enhancement effect of different components is different.In addition,the electron transfer capacity（ETC）was correlated with the degree of humification of compost.The electron donating capacity（EDC）of humus components in each treatment had no obvious change trend,but the electron accepting receptivity（EAC）showed a fluctuating upward trend,and the hydrophilic components were significantly lower than humic acid and fulvic acid.The maximum value of humic acid ETC in the experimental group reached a maximum of 117.32 and 125.62μmol e^-/g C,in 30 days.Compared with the control group,the maximum value of ETC in the fulvic acid group and the 5%biochar group increased by 10.61%and 18.43%,respectively.The maximum value of the hydrophilic component ETC in the 5%biochar group was higher than that in the control group,reaching116.98 and 51.70μmole^-/g C,respectively.After correlation analysis,a number of characteristic parameters characterizing the degree of humization of compost were correlated（P<0.05）with humus EDC,EAC and ETC,indicating that biochar not only deepens the humization degree of compost,but also improves the electron transfer ability of humus.