Effects Of Biogas Agitation Coupled With Micro-oxygen On CH₄ And H₂S In Anaerobic Digestion Of Pig Manure

More and more large-scale pig farms use dry and wet separation technology to separate manure,producing a large amount of manure with TS≥10%.Anaerobic digestion technology is widely used in the resource utilization of organic wastes,but for high solid wastes,the fermentation CH₄yield of this technology is low,and the produced H₂S will cause equipment corrosion and odor pollution.Therefore,it is of great significance to study how to enhance the CH₄yield and control the production of H₂S in high-solid swine manure.In this study,pig manure with 10%TS was used as raw material,and the CSTR fermentation process was used to study the effect of different stirring methods（mechanical stirring and biogas stirring）and adding trace O₂（0,36,72,108 and 143 m L/d）on CH₄production.The effects of biogas production rate and H₂S removal rate were analyzed,and the differences in the daily biogas production and its composition,physicochemical properties of fermentation broth,sulfur form and microbial community structure were analyzed,and the relationship between physicochemical factors,microorganisms and CH₄production rate and H₂S removal rate was revealed as follows:The development of high-solids pig manure anaerobic digestion reactor provides theoretical support.The main findings are as follows:（1）The effect of mechanical agitation on anaerobic digestion of pig manure showed that,compared with no agitation,mechanical agitation increased the daily yield of CH₄by 41.89%;while the concentration of H₂S decreased from 3180±155mg/m³to 3147±102 mg/m³.The average CH₄production rate and H₂S production rate of the raw materials were 0.33±0.02 L·g^-1（VS）and（0.39±0.07）×10^-3L·g^-1（VS）,respectively,by mechanical stirring.After anaerobic digestion,the bacterial and archaeal diversity indices in the reactor increased.In general,the gas production performance and stability of anaerobic digestion of pig manure under mechanical agitation were good,and a higher daily CH₄production was obtained.（2）The effect of biogas agitation on CH₄and H₂S in pig manure anaerobic digestion showed that compared with no agitation,the biogas return flow rate of 50L/d increased the daily CH₄production by 4.80%,while the average concentration of H₂S decreased.A drop of 6.84%.Total sulfide is the main chemical form of sulfur,accounting for 56.8%～88.1%of total sulfur.The dominant bacterial phyla,classes and genera in each treatment were Firmicutes,Clostridia and Clostridium＿sensu＿stricto＿1,compared with no stirring,biogas stirring increased the abundance of the second most dominant bacterial phylum,Bacteroidota,from24.36%to 28.88%.The dominant archaeal phyla,classes and genera of each treatment were Euryarchaeota,Methanosarcina and Methanosarcina,among them,the abundance of Methanosarcinia at 50 L/d was higher than that in the 0,25,100,150 and 200 L/d treatment groups,with the abundance ranging from 71.22%increased to 96.42%.（3）The effect of biogas agitation coupled with micro-oxygen on anaerobic digestion of pig manure showed that with the increase of micro-oxygen addition,the daily yield of CH₄decreased,and 36 m L/d reduced the daily yield of CH₄to a minimum of 17.18%.After adding micro-oxygen,24.18%～44.29%of O₂was dissolved in the reactor,resulting in the decrease of H₂S concentration.The dominant bacterial phyla,classes and genera in each treatment were Firmicutes,Clostridia and Clostridium＿sensu＿stricto＿1,in the archaeal community,the dominant bacteria at the phylum,class and genus levels were Euryarchaeota,Methanosarcinia and Methanosarcina.Compared with the experimental group,the abundance of bacterial and archaeal dominant phyla in the control group increased from 44.29%to 63.95%and 95.20%to 99.67%,respectively.Correlation analysis showed that H₂S production was positively correlated with p H,VFAs and dissolved sulfide in fermentation broth,and significantly negatively correlated with O₂.RDA analysis indicated that VFAs were the most important factor affecting bacterial and archaeal community structure.（4）Compared with no stirring,the daily CH₄production increased by 41.90%,12.79%and-10.97%,and the H₂S removal rates were 6.84%,64.43%,and 96.05%,respectively,under mechanical stirring,biogas stirring and biogas stirring coupled with micro-oxygen treatment.It can be seen that the daily output of CH₄in mechanical agitation is the highest,and the biogas agitation coupled with micro-oxygen has the best removal effect of H₂S.At the bacterial phylum level,the dominant bacteria of the four anaerobic digestion methods of pig manure are Firmicutes,and the abundance of mechanical stirring is the highest at 81.66%.at the genus level,the dominant bacteria of the four methods are inconsistent,no stirring,mechanical stirring and biogas.The dominant bacteria of stirring were Clostridium＿sensu＿stricto＿1（16.71%～32.89%）,while the dominant bacteria of biogas stirring coupled with microaerobic was Treponema（14.42%）.In the archaeal community,the dominant bacteria at the phylum,class and genus levels of the four ways were Euryarchaeota（98.40%～99.86%）,Methanosarcina（86.48%～96.42%）and Methanosarcina（86.48%～96.42%）.In conclusion,mechanical agitation has the highest daily CH₄output among the four agitation modes.Biogas agitation coupled with micro-oxygen agitation process can effectively remove H₂S,with a removal rate of 96%.