Effects Of Overload Induced By Different Load Lifting Methods On The Stability Of Anaerobic Digestion Of Pig Manure And Its Microbial Community Structure

In recent years,with the economic development and the improvement of people’s living standards,the pollution of livestock and poultry manure has become a problem that cannot be ignored.Anaerobic digestion(AD)treatment technology has the advantages of thorough and harmless treatment of manure,high added value of manure,and good economic benefits.It is currently a widely used livestock and poultry manure treatment mode.However,the existing large-scale livestock and poultry manure AD treatment plants have the problems that the actual operating load is generally low and the operating efficiency is not high.At present,domestic and foreign research mainly focuses on the introduction of overload disturbance by the traditional method of gradually increasing the load,or the influence of the types of organic substrates and additives,and there is little research on the method of increasing the organic load.In this context,in order to investigate whether the new jump load lifting method can improve the stability of the AD system of livestock and poultry manure,improve the critical point of system overload,and the reasons behind it.In this study,fresh pig manure was selected as the digestion substrate,and the semi-continuous AD reactor was operated at mesophilic temperature(36 ± 1 °C),and the reaction was induced by two methods: gradually increasing the load(R1)and jumping the load(R2).The device is overloaded and unstable.Through the analysis of physical and chemical indicators such as the operating efficiency and stability parameters of the AD system,and focusing on molecular biology methods such as Mi Seq high-throughput sequencing,the characteristic microorganisms in each period of the AD process were found,and the operating performance and performance of the anaerobic digestion reactor under different load enhancement methods were discussed.Responses of microbial community diversity and community structure.The main conclusions of this study are as follows:(1)The two load lifting methods have obvious effects on the operation efficiency of the livestock and poultry manure AD system,especially the gas production efficiency.The variation curves of specific methane production(SMP)obtained by the two load raising methods during the induced reactor instability process were significantly different in each load stage.Among them,the SMP curve under the jump lift load(R1)fluctuates continuously with the change of the organic loading rate(OLR)of the feed,and within the same average OLR period,the difference between the lowest point and the highest point of SMP keeps increasing;and The SMP curve of gradually increasing the load(R2)is relatively flat;and under the same OLR stage,the SMP value of R1 is always higher than that of R2.In addition,the change trend of volatile solids(VS)removal rate obtained in the process of inducing reactor instability by the two load lifting methods is similar,but under the same OLR stage,the level of VS removal rate of R1 is slightly higher than that of R2.(2)Stability indicators,such as p H value,volatile fatty acid(VFA)concentration and component ratio,total ammonia nitrogen(TAN),free ammonia nitrogen(FAN)concentration,the ratio of VFA to total alkalinity(VFA/TA)show that jumping the load can alleviate the ammonia inhibition effect to a certain extent.The changes of VFA/TA and VFA concentrations and their components indicate that VFA,the intermediate product of AD process in R1,exhibits higher conversion efficiency,which makes R1 have stronger buffering capacity against organic acids and corresponding stability,to reduce system acidification problems.Then comparing the parameter states under the same OLR in the stable period and the recovery period,it was found that the operating efficiency parameters SMP and VS removal rate had no significant difference,but the inhibitor TAN and VFA concentrations were significantly different(p<0.05),and the recovery period had lower The TAN and VFA of TAN and VFA showed that after the system experienced overload instability,the operating efficiency was restored to a higher level by reducing the OLR,and it had higher stability in terms of ammonia inhibition and acidification.(3)Based on Mi Seq high-throughput sequencing data,it was found that two different loading enhancement methods had no significant effect on the system microbial community richness index,but there were significant differences in the relative abundance of dominant microorganisms in the microbial community.The microbial community structure analysis at each stage showed that the microbial community structure that regained stability after experiencing systemic acidification and instability was significantly different from the community structure in the stable period,and the microbial community structure that could withstand higher loads was succeeding.(4)The dominant phyla in the AD process of the R1 and R2 systems are Bacteroidota,Firmicutes,and Spirochaetota,whose members are mainly involved in the hydrolysis and acidification of organic matter.The characteristic microorganisms are Ruminofilibacter,Syntrophomonas,Hydrogenispora and other bacteria involved in the hydrolysis and acidification stage,Candidatus Cloacimonas,Clostridium sensu stricto 1,Treponema and other hydrogen-producing acid-producing bacteria involved in the acetic acid stage,and DMER64 as the main hydrogen carrier.Compared with the traditional step-lift load(R2),the skip-lift load(R1)has a higher relative abundance of hydrolytic-acidifying bacteria and hydrogen-producing acetogens.It is speculated that this may be due to the higher operating efficiency and stability of R1.s reason.(5)The main methanogenesis pathways in the stable stage of AD system in both the skip-lifting load and the step-by-step loading are the acetate-type methanogenesis pathway,and Methanosaeta is the dominant methanogen.After acidification instability,Methanosaeta was still the dominant methanogen in R1 during the instability phase,and Methanosarcina was the dominant methanogen in the recovery phase,but the methanogenesis pathway of the system was always the acetate-type methanogenesis pathway.During the period,the main methanogens changed to Methanosarcina,and the main methanogenesis pathway changed to hydrogen-type co-action.