| The development of biogas engineering can realize the efficient use of resources,which is conducive to the construction of a resource-saving and environment-friendly society.Since chicken manure contains a large number of nitrogenous substances,it is the main factor that forms the ammonia inhibition problem in anaerobic digestion,which affects the stable operation of chicken manure anaerobic digestion.Biochar,with its more developed pore structure and specific surface area,can alleviate the inhibition caused by high ammonia nitrogen concentration to a certain extent through adsorption behavior,but its adsorption capacity is limited and cannot meet the demand of the digestion process.At the same time,it is also difficult to recover and recycle biochar,which leads to an increase in related costs.Based on the above problems,it is proposed to construct nano-Fe3O4 biochar to enhance its application potential in anaerobic digestion systems.In addition,the intervention of nano-Fe3O4 biochar is able to enhance the direct electron transfer capacity between microorganisms.Therefore,in this paper,biochar was prepared from corn stover at 550℃and loaded with Fe3O4 magnetic nanoparticles by solvothermal method to generate nano-Fe3O4 biochar.It was added to chicken manure anaerobic digestion system in different proportions,and the mechanism of its effect on anaerobic digestion of chicken manure under high ammonia nitrogen concentration was investigated by sequential batch and semi-continuous anaerobic digestion tests.The details of the study are shown as follows:（1）The nano-Fe3O4 biochar（MS550）was generated by loading Fe3O4 nanoparticles on corn stover biochar（CS550）through the solvothermal method.The structural characterization results showed that MS550 was able to maintain the porous structure of corn stover mesh,and also had good magnetic separation ability.Compared with CS550,MS550 had more hydroxyl groups on its surface,which provided more adsorption sites for ammonia nitrogen adsorption.The highest ammonia nitrogen adsorption capacities of CS550 and MS550 were 20.6 mg/g and19.2 mg/g at 25°C,respectively,and the differences in their adsorption capacities for ammonia nitrogen were not significant.MS550 did not affect the adsorption capacity of biochar because the loading of Fe3O4 nanoparticles blocked the pore channels,and the adsorption behavior of both for ammonia nitrogen was mainly multi-molecular layer adsorption.（2）The addition of CS550 and MS550 to the anaerobic digestion of chicken manure at 5%,10%,and 15%,respectively,and the results showed that CS550 had only a small increase in methane production,but the addition of MS550 significantly increased methane production by up to 62.61%.Combined with the changes in ammonia nitrogen concentration,it can be found that the ammonia nitrogen concentration remained around 5 g/L after the addition of MS550,indicating that the adsorption effect of nano-Fe3O4 on ammonia nitrogen in chicken manure anaerobic digestion system was limited.Chloroflexi and Methanosarcina,which are potential direct electron transfer partners,were enriched after the addition of MS550.the relative abundance of Chloroflexi increased from 0.52%to 3.51%and Methanosarcina increased from27.50%to 49.30%,which indicated that the effect of nano-Fe3O4 on ammonia inhibition was alleviated mainly in terms of direct electron transfer between microorganisms,and the increase in methane production was associated with direct electron transfer between microorganisms.（3）After further selection of the optimal dosage,it was found that the degradation of acetic acid under high ammonia nitrogen concentration mainly depended on the syntrophic acetate oxidation pathway,and the addition of MS550 enriched the syntrophic acetate oxidation bacteria unclassified Clostridiales and methanogenic Methanosarcina with direct electron transfer ability,which led to the further improvement of the performance of methanogenesis from anaerobic digestion of chicken manure under high ammonia nitrogen concentration.（4）After good gas production was obtained by sequential batch anaerobic digestion,a pilot study of semi-continuous anaerobic digestion of chicken manure was subsequently carried out.At an organic load of 0.625 g VS·L-1d-1,it was found by daily biogas production that the presence of MS550 improved the stability of the chicken manure anaerobic digestion system and facilitated a steady increase in daily biogas production.However,the presence of Fe3O4 magnetic nanoparticles did not seem to play an obvious role when the organic load was raised to 3.125 g VS·L-1d-1,mainly due to the insufficient contact of nano-Fe3O4 biochar with the feedstock after raising the organic load and the insufficient recovery of nano-Fe3O4 biochar from the effluent feed solution,resulting in the reduction of the relative content of nano-Fe3O4 biochar in the system.In this study,the anaerobic digestion process of nano-Fe3O4 biochar under high ammonia nitrogen concentration was investigated,and the mechanism of its alleviate effect was studied to provide theoretical guidance for the stable and efficient operation of anaerobic digestion systems with high ammonia nitrogen substrates,which is of great scientific significance to promote the development of large-scale biogas projects for organic wastes with high nitrogen content,such as livestock and poultry manure. |
