Efficient Anaerobic Digestion Process And Microbial Characteristics Of Stover By Digestate And Zero-valent Iron Enhancing Hydrolysis And Acidification

The yield of corn stover(CS)in China is huge,and are the topic agricultural organic solid waste.If the great amount of CS can not be treated in time,it can easily lead to a wide range of envirionmental problems.Anaerobic digestion technology is used to treat CS.It can not only alleviate the energy shortage problem,but also can avoid the environmental pollution caused by the burning of CS.In view of the poor biodegradability and low conversion efficiency of lignocellulosic materials such as CS,this study proposes to improve the biodegrability and biogas production performance of CS by digestate and zero-valent iron enhancing hydrolysis and acidification performance and improving anaerobic digestion process.The main research contents and results are as follows:(1)The effect and mechanism of digestate-enhancing hydrolysis and acidification of CS were studied.Through the batch experiment,the gas production regulation,substance degradation regulation and the production and transformation of intermediate products in the process of hydrolysis and acidification were analyzed,and the reasons for the high efficiency degradation of CS by hydrolysis and acidification were systematically analyzed.The results showed that the methane yield and energy recovery rate of CS increased significantly after hydrolysis and acidification,which were 265.1 mL g-1 VS-1 and 57.91%,respectively.The benzene ring,ether bond,ester bond,hydrogen bond,and ?-(1?4)glycosidic bond in lignocellulose were all destroyed by FTIR analysis.It was also shown that the acidification modification can degrade the lignin monomer compound,and the macromolecular polymer was degraded into the low molecular weight aromatic compound and acetic acid.Therefore,acidification modification is an effective treatment method for improving the biodegradability of lignocellulose.(2)Digestate-enhancing hydrolysis and acidification of CS environmental factors and microbial community structure changes are studied.The effects of acidification time,substrate and innoculum ratio,pH and temperature on the hydrolysis and acidification performance of CS and microbial community structure were analyzed by single factor experiments.The results showed that the yield of VFAs from CS was best when the acidification was 8 d,the ratio of substrate and inoculum was 4,the temperature was 45? and pH was 10.The hydrolysis efficiency,VFAs concentrstion and composition,biogas production and microbial community were different under the different environmental factors,indicating that the environmental factors determine the microbial community structure,and microbial community structure affect hydrolysis and acidification.In the substrate and inoculum ratio of 4 group,the abundance of unclassified_f_Ruminococcaceae and Mobilitalea was higher than that of the other groups.Clostridiaceae 1 and Ruminococcaceae have higher abundance at 45 ? and pH=10.(3)The parameters optimization of the digestate-enhancing hydrolysis and acidification model of CS were studied.A set of VFAs production process conditions from CS was established by simulating the VFAs by response surface and artificial neural network model.The results showed that the optimal fermentation parameters were:temperature 40?,acidification time 8 d,inoculation ratio 4,pH 10.The predicted results of response surface and artificial neural network model were consistent.The VFAs concentration was 11477.8 mg L-1 on the condition of the optimal acidification.The interation between HRT and pH was significant also with T and pH,and the interaction between other variables was not significant.The discharge of acidogenic phase is used as the feeding for methanogenic phase with methane production experiment.On the condition of the optimal acidogenic parameter,the unit loading methane yield was 285.0 mL g-1 TS-1,which was 8.4%higher than the acidification center point.(4)Zero-valent iron enhancing hydrolysis and acidification of CS and microbial community structure changes are studied.By adding zero-valent iron to regulate the ORP to change the acidogenic fermentation pathway,and strengthen the VF As production performance.The effects of different forms of zero-valent iron(iron filings,iron powder and nano-iron)on VFAs concentrations,gas components,ORP and microbial community structure were investigated,and the regulation mechanism of zero-valent iron enhancing hydrolysis and acidification was explored.The effect of zero-valent iron on the acidogenesis and methanogenesis of CS was studied.The results showed that zero-valent iron promoted the conversion of propionic to acetic,and the impact loading resistance of the acidogenic phase reactor was enhanced.The propionic and butyric were reduced from 27.7%-41.2%and 6.9%-10.7%to 4.5%-10.4%and 4.2%-7.4%,respectively,and the acetic concentration was increased from 43.9%-54.1%to 74.8%-85.8%.The increase of relative abundance of Peptostretoccaceae in the nano-iron treatment group is beneficial to the formation of[2Fe-2S]and[4Fe-4S],and is an important component of ferredoxin(electron transfer protein)in methanogenesis.Therefore,the addition of nano-iron can increase the methane production in the acidification stage and accelerate the methane production process in the methane phase.(5)One-stage,two-stage and three-stage anaerobic digestion processes and microbial community structure changes of CS were studied.Based on the principle of hydrolysis and acidification,three-stage anaerobic digestion process was proposed to compare the anaerobic digestion performance and microbial characteristics of CS with one-stage and two-stage systems under different organic loading rate(OLR)conditions,and the anaerobic digestion process with better performance was obtained.The anaerobic digestion performance of one-stage,two-stage and three-stage systems on the different OLR conditions was studied.The results showed that the methane yield per unit VS was 215.3-301.1 mL g-1 VS-1 at the OLRs of 1.4,1.6 and 1.8 g TS L-1 d-1,which was 23.5%-50.5%higher than that of one-stage.The stability and energy ratio of the three-stage system were higher than those of two-stage and one-stage system.Combined with microbial community structure analysis,Ruminococcaceae and Syntrophomonadaceae have higher relative abundance in the ? stage reactor in the three-stage system,which is beneficial to the degradation of cellulose and VFAs.In summary,the digestate and zero-valent iron enhancing hydrolysis and acidification and three-stage anaerobic digestion process can effectively improve the hydrolysis and acidification performance of CS,enhance the biodegradability,optimize the microbial community structure and the metabolic pathway of methanogenesis.It provides a new technical approach for engineering use.