Effect Of Psychrophilic Methanogenic Microbial Consortia For Bioaugmentation On Corn Straw Psychrophilic Anaerobic Digestion

Anaerobic digestion is one of the significant ways of resource treatment of agricultural waste and develop renewable energy,which can degrade organic wastes and produce methane and organic fertilizers.Due to the large temperature difference between the south and north of China,the development of biogas industry in low-temperature and cold regions could lengthen the lag phase,mainly manifested by low efficiency of biogas production,high cost of thermal insulation,and difficulty in stable operation throughout the year.However,the north is a region where crop cultivation and livestock and poultry breeding are relatively concentrated,and biomass resources are abundant.Breaking through the technical bottleneck of low-temperature anaerobic digestion and improving gas production performance are of great significance for promoting the development of the biogas industry in the cold regions of the north.Bioaugmentation technology by adding functional bacteria is one of the means to achieve inhibition and efficiency enhancement in anaerobic digestion.In this study,the bioaugmentation of psychrophilic propionate-degrading consortia(the mixture of propionic-degrading consortia and acetogenic methanogen)was conducted to boost anaerobic digestion of corn straw in psychrophilic reactors.The optimal dosage of bioaugmentation seed was determined through batch anaerobic digestion experiments.The optimal dosage and frequency of bioaugmentation seed were determined through sequential batch anaerobic digestion experiments,and the synergistic reinforcement effects of psychrophilic bacteria and trace elements(Fe,Co,Ni)were explored through demi-continuous anaerobic digestion.Evaluate the effect of bioaugmentation through statistical and kinetic analysis,and reveal the mechanism of bioaugmentation through microbial composition and succession.The specific research content and main conclusions are as follows.In batch anaerobic digestion experiments,with the different dosages of3%,6%,9%,12%,15%,and 18% at low temperature(20°C).To investigate the optimum dosage and corresponding mechanism,the reactor performance,microbial metabolites,and microbial community dynamics were analyzed.The results showed that bioaugmentation consortia could improve methane production rate under a psychrophilic anaerobic environment,as evidenced by 1.3 to 2.4 times increase in bioaugmented groups compared to the control group(without bioaugmentation).Within the certain range of 3% to 12% of bioaugmentation dosage,it was positively correlated with the methane yields.This means the optimal dose was 12%,and the accumulative methane yield was 66% than that of the mesophilic control group.Kinetic analysis shows that bioaugmentation could shorten the anaerobic fermentation cycle,i.e.,shorten T80(the time required to reach 80% of total methane production)by12-19 days.Microbial community analysis showed that bioaugmentation increased the relative abundance of methanogens Methanothrix and Methanosarcina in the anaerobic fermentation system.In the sequential batch anaerobic digestion experiment,the effects of different bacterial addition batches(3% * 4 times,2% * 2 times,12% * 1time)on the methane production performance of straw were compared under the same total bioaugmentation cultures addition dosage(12%).It was found that different frequencies of bioaugmentation could promote anaerobic digestion performance,and the methane production rate decreased with increasing the addition frequency.The optimal batch of bioaugmentation bacteria was 12%*1 time,increasing the methane production rate by24%~72%,reaching 68%~82% of the straw mesophilic(37 ℃)control reactors.Intermediate product analysis showed that the cumulative amount of volatile fatty acids in each batch gradually decreased with the increase of reaction time.The analysis of microbial community showed that bioaugmentation mainly improved the relative abund ance of methanogenic bacteria Methanothrix in the anaerobic digestion system.In the long-term anaerobic digestion process,the methane production rate is related to the initial bioaugmentation seed addition amount,and both low or repeated addition of bioaugmentation seed and adding indigenous inoculum cannot significantly improve the methane production rate.In semi-continuous anaerobic digestion experiment,the synergistic effects of periodic addition of psychrophilic methanogenic bacteria(6% and12%)and trace elements(Fe:1.0 mg·L-1·d-1,Co:0.4 mg·L-1·d-1,Ni:0.4 mg·L-1·d-1)on the methanogenic performance of straw were compared.It was found that the addition of bioaugmentation seed alone and synergistic addition of trace elements can promote anaerobic digestion performance,and the methanogenic performance of the higher dosage reactors was stronger than that of the low dosage reactors.The best effect is to add 12% bioaugmentation cultures and trace elements to promote methane production.,which the methane production rate reaches 71%~124% of that of straw mesophilic(37 ℃)control reactors.The psychrophilic control reactors be defeated within 90 days,severely inhibiting methane production.Microbial community analysis showed that adding psychrophilic methanogenic bacteria and microelements to enhance the relative abundance of methanogenic archaea,Methanothrix and Metanobrevibater,in the psychrophilic straw anaerobic fermentation system.In batch,sequential batch and semi-continuous anaerobic fermentation systems,the addition of psychrophilic methanogenic bacteria can improve the psychrophilic anaerobic fermentation performance of straw,promote the hydrolysis of straw and the degradation of volatile fatty acids,shorten the low-temperature anaerobic fermentation cycle,improve the methanogenic potential,and provide a theoretical basis for low-temperature engineering anaerobic fermentation.