Characteristics And Mechanism Of Anaerobic Digestion Of Pig Wastewater Mediated By Zerovalent Iron Biochar

The rapid development of livestock and poultry breeding has caused serious environmental pollution.However,traditional anaerobic digestion has some problems such as low methane-producing efficiency,insufficient hydrolysis and easy acidification.In this paper,biochar（BC）,zero-valent iron（n ZVI）and nano-zero-valent iron biochar（n ZVI/BC）were added to improve the anaerobic digestion performance of pig wastewater during anaerobic digestion,and the effects of exogenous additives on anaerobic digestion performance were systematically analyzed.The changes of anaerobic microbial community structure induced by exogenous additives were investigated.The influence law of anaerobic treatment on the anaerobic system is described,which provides useful guidance for continuous optimization of anaerobic treatment technology of pig farm wastewater.Centering on the construction of this idea,the following work is carried out in this paper:（1）In this paper,n ZVI/BC was prepared by pyrolytic and liquid phase reduction method.Multiple characterization methods were used to analyze the results.The results showed that the BC pore structure was rich,and the increase of pyrolysis temperature resulted in the decrease of functional groups on the surface of biochar and the increase of specific surface area.The n ZVI has smaller particle size and more block structures.The morphology of n ZVI load on 300BC was different from that on500BC.The n ZVI load on 300BC was villous,and n ZVI load on 500BC was clear and granular,with small and uniform particle size.（2）By adding BC,n ZVI and n ZVI/BC to the anaerobic digestion system of pig wastewater,it was found that exogenous additives all increased methane production and methane content.The cumulative methane yield of n ZVI/500BC0.5 4 g/L was the highest,reaching 3350.67 m L,93.67%higher than that of the control group.The overall variation trend of biogas components was that the CH₄gas content increased while the CO₂content decreased.The n ZVI/500BC significantly increased the ratio of CH₄and CO₂in biogas,which was positively correlated with the addition amount.BC,n ZVI and n ZVI/BC significantly reduced H₂S content in biogas,and n ZVI/500BC0.5had the best effect,and the overall methane content was also higher.（3）After 15 days of anaerobic microbial treatment,the COD degradation rate in each group was higher than that in the control group.The COD degradation rate in n ZVI group was the highest,reaching 84.82%,22.40%higher than that in the control group.The COD degradation rate corresponding to n ZVI/500BC2 4 g/L was the highest,reaching 83.37%.The effect of n ZVI/500BC on TVFA degradation was the best,and the synergistic effect of n ZVI and 500BC reduced the TVFA concentration to below 200 mg/L.The p H remained at 7.0-8.0 during the whole anaerobic digestion process without acidification.（4）The 300BC has improved the relative abundance of Desulfobacterota and Halobacterota.The 500BC promoted the growth of Bacteroidota,Firmicutes and Euryarchaeota,which was the reason for the increase of TVFA concentration and methane production.The increase of n ZVI concentration led to the increase of the relative abundance of Methanobacterium and Methanosaeta,which improved the DIET of microorganisms.The addition of n ZVI/300BC increased the relative abundance of Bacteroidota,Firmicutes and Spirochaetota.Under the stimulation of n ZVI/500BC0.5,the relative abundance of Euryarchaeota microorganism increased from 1%to 33.7%,and the relative abundance of Bacteroidota microorganism increased from 16%to 23%.The relative abundance of Euryarchaeota microbes is mainly Methanobacterium,which is a Methanobacterium with H₂/CO₂as substrate,which can reduce CO₂level in biogas,improve methane content,and further improve methane production.