Bioaugmentation Of Methanogenic Propionate-degrading Microbial On Psychrophilic Batch Anaerobic Digestion

Anaerobic digestion（AD）is one of the important ways of resource treatment of agricultural waste,which can effectively contribute to the realization of carbon neutrality.However,AD is usually limited by region and season,especially the low temperature environment leads to the reduction of fermentation microbial activity,which seriously hinders the development of biogas engineering in cold areas.Therefore,the bottleneck problems such as low biogas production and long fermentation cycle need to be solved urgently.The core of breaking through the psychrophilic AD is to strengthen the metabolic pathway of dominant methanogenic microorganisms,so as to enhance the psychrophilic AD performance and improve the degradation efficiency of microorganisms.Based on this,this paper studied the bioaugmentation of two different types of methanogenic propionate-degrading microbial on psychrophilic batch AD with cow manure and corn straw as substrates at 20℃.By adding different doses of bioaugmentation seeds（BS）,the bioaugmentation effects on biogas production performance and related fermentation indexes,microbial community structure succession were evaluated respectively.The purpose of this study is to improve the performance of psychrophilic AD through bioaugmentation,clarify the appropriate type and dosage of BS,and interpret the principle of bioaugmentation on psychrophilic AD,so as to provide a theoretical reference for the application and promotion of large-scale biogas engineering in cold areas.The main contents and conclusions are as follows:（1）In the psychrophilic AD system,4%（R1）,8%（R2）,12%（R3）,14%（R4）and 16%（R5）of mesophilic BS were added respectively,and the bioaugmentation effects of different doses were compared.The results showed that compared with the control group（RC）,mesophilic BS could effectively improve the biogas production performance,and within a certain dose range,the fermentation performance was positively correlated with bioaugmentation doses.The biogas production performance of each treatment is R4>R5>R3>R1>R2>RC,and the methane production of R4（36.00mL/g VS）is 4.20-fold higher than RC,T₈₀shortened by 22 d.Mesophilic BS can accelerate the degradation of volatile fatty acids（VFAs）and alleviate acid accumulation,and the degradation efficiency increased by 23.73%-52.37%.The degradation of acetate and propionate is the most significant.The degradation efficiency of acetate increased by 24.29%-51.57%,degradation rate accelerated by 34.85%-59.09%;Propionate increased by 13.63%-67.77%and 21.21%-34.85%respectively.Bioaugmentation can maintain the stability of the system.Compared with RC,the p H change of the enhanced system is smaller.Mesophilic BS are closely related to the change of archaeal community structure.Methanothrix（52.78%-76.46%）is the dominant（2）communities in bioaugmentation reactors,which belongs acetoclastic methanogens.Its relative abundance increases linearly with bioaugmentation dose.Moreover,Methanothrix also occupies a dominant position in mesophilic BS.On the basis of mesophilic BS,the psychrophilic methanogenic propionate-degrading microbial were domesticated by stepwise cooling,and the bioaugmentation effect of psychrophilic AD was evaluated.The dosage was the same as that of mesophilic BS,which were 4%（T1）,8%（T2）,12%（T3）,14%（T4）and 16%（T5）,respectively.TC was the control group.Moreover,a group of 16%concentrated inoculum experiment was added as comparison（TIno）to identify the correlation between AD performance and bioaugmentation.The result showed that compared with mesophilic BS,the biogas production performance of psychrophilic BS is more significant,biogas production at T3 is the best,and methane production is 72.20 mL/g VS,which is 4.74-fold higher than TC,T₈₀shortened by 34 d.In the corresponding dose range,the bioaugmentation effect was positively correlated with the BS dose.The biogas production performance of each treatment was T3>T4>T5>T2>T1>TIno>TC.In terms of degradation of organic acids,psychrophilic BS have a more significant effect on the degradation of acetate.The degradation efficiency of acetate increased by 29.98%-52.95%,and the degradation rate accelerated by 73.33%-86.67%.The bioaugmentation of psychrophilic BS also has a significant effect on the structure of archaea community.After bioaugmentation,Methanosarcina（50.90%-58.26%）and Methanothrix（36.26%-46.63%）are the absolute dominant communities,and exist for a long time.The former use three substrates to produce methane,and the latter use acetate.Both are also the dominant communities in the psychrophilic BS.Compared with psychrophilic bioaugmentation,the increase of microbial biomass in the inoculum did not significantly promote the AD performance.The main reason for the improvement of psychrophilic AD performance was to increase the biomass of functional methanogenic microbial through bioaugmentation and strengthen the methanogenic metabolic pathway in the downstream stage of fermentation.Comprehensively analyzed the bioaugmentation effect,the same dose of psychrophilic BS has a higher enhancement effect on methane production,shorter fermentation cycle and more advantages in degrading VFAs.The dominant microbial Methanosarcina has better environmental adaptability and higher physiological activity in the system.Psychrophilic BS is more suitable for AD at 20℃,with less dosage（12%）,faster fermentation process and more efficient improvement of biogas production performance.