Preparation Of Fruit Branch Biochar And Its Effect On Anaerobic Digestion Of Different Raw Materials

The organic waste has a high output and a variety of types in China.During the treatment process,it will produce a large odor and carry a large number of pathogenic bacteria,which can spread diseases and seriously damage the urban and rural ecological environment.In order to further promote the construction of ecological civilization,speed up rural revitalization and environmental pollution prevention,it is very important to realize the harmless,reduction,resource or energy utilization of organic waste.Compared with other technologies,anaerobic digestion has low energy consumption,good technical safety and high energy conversion efficiency.It is very suitable for the recycling of various organic wastes such as kitchen waste,crop straw,livestock and poultry manure,sewage sludge,etc.In this study,biochar was prepared from kiwi fruit and apple stubble,and then modified and characterized.Eight kinds of biochars were added to the single anaerobic digestion of food waste at 3 and 7g/L respectively,and the biogas production performance,kinetic parameters,stability parameters and microbial community structure were analyzed to explore the effect of biochar on food waste.Then,the biochar with the best biogas production effect was applied to the co-digestion system of food waste,chicken manure and wheat straw to further explore the synergistic effect of biochar and co-digestion.Concluded as follow:（1）The physicochemical properties of biochar were affected by the raw materials.The yield and ash content of biochar from apple branches were higher than those from kiwi fruit branches.The p H values of the biochar from kiwifruit and apple branches were M0=8.36and P0=8.53,respectively.The electrical conductivity of kiwifruit branch biochar was significantly higher than that of apple branch biochar,M0=667μS/cm and P0=468μS/cm,respectively.Modification will affect the p H value and electrical conductivity of biochar,HNO₃modification can reduce the p H value of biochar and electrical conductivity,Na OH modification can increase the p H value and reduce the conductivity of biochar,Fe Cl₃modification has the opposite effect.Apple branch biochar has more abundant pore structure,and its specific surface area and total pore volume are 6.30 times and 2.68 times that of kiwi branch biochar,respectively.The modification also changed the microstructure of biochar.The specific surface area of Na OH modified biochar increased,while that of HNO₃ and Fe Cl₃ modified biochar decreased.（2）Compared with CK,the biogas production of each biochar test groups increased by9.88-50.43%,and the methane production increased by 11.97-69.68%.When the addition amount is 3g/L,the unmodified biochar has the best methane production,and the value is327.90m L/g VS,which is 56.78%higher than that of CK;when the addition amount is 7g/L,the methane production of the Na OH modified biochar is the best,the methane production was 354.89m L/g VS,which was 69.68%higher than that of CK.Kinetic analysis shows that,compared with CK,the biogas potential of experimental groups is increased by13.77-51.65%and the lag period is shortened by 32.58-67.94%.The effect of biochar on hydrolysis constant（k）was not significant,but there was a significant negative correlation between hydrolysis constant and demurral period（p<0.01）,for example,Na OH modified M1-7 has a maximum k of 0.0599 and a minimum lag period of 1.81±0.13d.Biochar can accelerate the conversion of VFA,increase the p H value,and shorten the lag period.Biochar can increase the relative abundance of Bacteroidetes,Synergistetes,Proteobacteria and Methanosarcina,and promote microbial degradation of organic matter to produce methane.As a conductive material,biochar can mediate direct interspecific electron transfer（DIET）between bacteria and archaea and increase methane production.（3）The co-digestion of food waste and chicken manure or wheat straw has obvious synergistic promotion effect,and the system benefit coefficients based on biogas and methane production are 8.06-22.22%and 11.03-27.55%,respectively.When the kitchen waste is mixed with chicken manure or straw,the biogas promotion effect is the best when the mixing ratio is 1:1,and the methane promotion effect is the best when the mixing ratio is 1:3.Both biochar can improve the biogas and methane production of co-digestion,and the system benefit coefficients based on biogas and methane production are 6.96-18.64%and 11.18-28.44%,respectively.Biochar and co-digestion can increase p H,accelerate VFA conversion,and regulate ammonia nitrogen levels,thereby creating a more suitable environment for anaerobic digestion.