Biochar And Nano Zero Valent Iron Promote Anaerobic Fermentation Chain Elongation To Produce Caproic Acid

With the development and progress of The Times,people’s demand for energy is increasing.However,the traditional fossil energy is non-renewable and has been facing exhaustion,so it is an inevitable trend of the development of The Times to find a green alternative energy.In the study of new energy sources,it is found that biomass energy is not only easy to obtain,low cost,but also can promote the production of caproic acid through anaerobic fermentation.Caproic acid can be used as raw materials for biofuels,pharmaceuticals and organic solvents.It is a product with high heat and high added value.Therefore,biological production of caproic acid is in line with the energy concept of recycling waste resources and sustainable development,and has become a research hotspot in recent years.The available biomass energy mainly includes agricultural straw,kitchen waste,wine cellar mud and other production and domestic wastes,among which the wine cellar mud is rich in Clostridium kluyveri,which is unique in Clostridium spp and it is also the dominant group in the process of chain elongation.Because it can promote the fermentative conversion of ethanol and acetic acid into butyric acid and caproic acid,and can also promote the chain elongation of Short chain fatty acids(C2～C4)to Medium chain fatty acids(C5～C8)through reverse β-oxidation,so wine cellar mud is considered as a kind of high quality bioenergy producing caproic acid.Usually,the wine cellar mud can release carbon source as electron acceptor during the hydrolysis and acidification stage.After adding ethanol as electron donor,the production of caproic acid is promoted under the action of Clostridium kluyveri.But the yield of caproic acid obtained by this method is low.It has been shown that conductive materials can promote the process of producing caproic acid and increase the yield of caproic acid.Therefore,this paper explored the effect of pretreatment and biochar coupled nano-zero-valent iron on the system of producing caproic acid,and designs the optimal experiments of biochar and modified biochar,as well as nano zero valent iron and high purity iron powder.Experimental results showed that chemical pretreatment could retain the high specificity of Clostridium,enhance the competition of the dominant caproic acid producing bacteria,and also obtain more electron acceptor content.After chemical pretreatment,the yield of caproic acid can be increased by 42.4%,and the yield of caproic acid can be increased by 67.67% after adding biochar again,and the maximum yield has reached 3.8 g/L.Under the promotion of nano zero valent iron,the content of caproic acid can also be significantly increased,and the promotion effect of high concentration of nano zero valent iron is significant,and the maximum promotion efficiency can be increased by 45.41%,which may be related to the magnetic characteristics of nano zero valent iron can significantly promote the direct interspecific electron transfer.Continuous reactor is a kind of biological reactor commonly used in anaerobic fermentation,which can accelerate the reaction and promote the transformation of substrate to the target product.Therefore,the effect of continuous reactor on the production of caproic acid was investigated in this paper after the batch experiment.It was proved that the continuous reactor could not only promote the generation of caproic acid,but also promote the hydrolysis of inoculation pit mud.Compared with batch experiment,continuous feeding at low rate not only obtained higher yield of caproic acid(15.99% higher than batch experiment),but also obtained more Short chain fatty acid products(10.38 g/L).However,in the continuous feeding,due to the influence of discharging mode and material enrichment after feeding,long-term reaction is not conducive to control,easy to cause material waste.Therefore,in the future continuous reactor research,the hydraulic residence time of the reaction can be reduced or the formation of caproic acid can be promoted by two-stage reaction.At the end of this paper,the biochar and nano zero valent iron were coupled to explore whether the composite material could promote the production of caproic acid and whether it could promote the hydrolysis of the active pit mud.It was found that biochar and nano zero valent iron not only have synergistic effect,but also can alleviate the adverse effects of single carbon material and iron material on the experimental system,making the reaction environment of acid production system more stable than that of single carbon material or iron material.The acid production of the system was analyzed.It was found that the doped composite could obtain a higher yield of caproic acid(5.3 g/L)and a higher yield of VFAs(7.8 g/L).Compared with the control group,the yield of caproic acid increased by 1.33 times.This research mainly confirm the biochar coupled nano zero valent iron in caproic acid producing system feasible,and the coupling of material to provide attachment sites for microbial,avoid agglomeration of nano zero valent iron,also can promote the growth of the advantages of caproic acid bacteria,enhance competitive flora,for subsequent composite materials to promote production the research provides the foundation and basis of caproic acid.