Study On Enhanced Anaerobic Digestion Of Cow Dung With Iron Modified Biochar Based On Biogas Residue

More than 40%of the animal waste produced in China every year is not fully utilized,resulting in serious waste of resources and environmental pollution.Anaerobic digestion is an economical and efficient way to treat a large amount of livestock and poultry waste,but it has some problems such as slow reaction rate of organic hydrolysis and low methane production efficiency.Therefore,how to improve the anaerobic digestion rate and develop new and efficient anaerobic digestion process is the focus of current development.The way of adding biochar to the anaerobic digestion system is one of the commonly used processes,but there is still room for improvement in methane production efficiency.In this study,iron-modified biochar was used to study the effects of composite materials on the gas production performance of anaerobic digestion of cow dung,fermentation broth stability and microbial community structure by adding iron modified biochar during anaerobic digestion.The main conclusions are as follows:(1)Iron-modified biochar based on biochar was successfully prepared by impregnation with ferric salt solution and pyrolysis of precursor at 800℃.Iron element was loaded on the surface of biochar in the form of zero-valent iron.After biochar modification,The results show that the alkalinity increased,the Zeta potential increased to-35.20 m V,and the chemical stability in the solution was enhanced.Zero-valent iron modified biochar Iron modification has more abundant functional groups and oxygen-containing functional groups.It also has a hierarchical porous structure and higher specific surface area of 355m~2/g and the total pore volume reaches 0.220 cm3/g,which is 2.47 and 1.75 times higher than that before modification.(2)In batch experimental,the effect of zero-valent iron modified biochar on the anaerobic digestion of cow dung was studied.When the addition amount of zero-valent iron modified biochar was more than 10 g/L,the improvement effect was significant,the biogas production increased by 17.75%～26.81%,and the cumulative methane production increased by 30.69%～36.31%,zero-valent iron modified biochar could improve the methane content.During the reaction,the p H showed a trend of decreasing first and then rising,which was consistent with the changing trend of VFA.After the reaction,the concentration of ammonia nitrogen and SCOD in the treatment group decreased to a certain extent.When the supplemental amount of iron-modified biochar was 10-20 g/L,there was no significant difference in enhanced digestion.Considering the cost and performance,the optimal addition level of zero-valent iron modified biochar is 10 g/L,the methane content of the system reaches 65.83%,the cumulative gas production increases by 17.85%,the cumulative methane production increases by 30.69%,the maximum gas production rate is 66.90 m L/d.(3)The zero-valent iron modified biochar created favorable growth conditions for microorganisms and changed the diversity of microbial community.The dominant bacteria groups are Firmicutes,Bacteroidetes,Spirochaetae and Chloroflexi.Adding zero-valent iron modified biochar increases the relative abundance of Firmicutes and Chloroflexi,which promotes the hydrolysis acidification process.The dominant archaea were Methanobacterium and Methanobrevibacter,which were hydrogen trophic methanogenic.zero-valent iron modified biochar increased the abundance of Methanomassiliicoccu,and affected the structural changes of microbial community in the anaerobic digestion system of cow dung,increased the pathway of methane production,so that methane production increased.