Study On Immobilization Method Of Microbial Agent In Aerobic Composting

The rapid growth of organic solid waste production has caused huge environmental pressure.It is an inevitable trend to realize the recycling of organic solid waste resources in the future.Aerobic composting is one of the effective ways to utilize organic solid waste.The development of microbial agents for aerobic composting has become a research hotspot in the field of solid waste.Compared with liquid microbial agents,solid microbial agents are more conducive to transportation and preservation,and have significant advantages in industrial production and application.However,there are many non-spore bacteria in the aerobic composting agent,which have weak stress resistance and mostly exist in liquid form,and are easily inactivated after immobilization.Therefore,it is necessary to study appropriate immobilization methods to improve the survival rate of the bacteria.In this study,the compound microbial agent for aerobic composting of liquid kitchen waste prepared in the laboratory was taken as the research object.The preparation process of solid microbial agent,the optimization of immobilization conditions,the optimization of microbial agent drying conditions and the optimization of compound drying protective agent conditions were explored.The dynamic changes of microbial community before and after immobilization and during storage were analyzed.The specific results are as follows:（1）The maximum number of viable bacteria was determined at 48 h,which was the best harvest period of the microbial agent,by determining the growth curve of the aerobic composting agent;The optimum conditions for centrifugal collection of the bacteria agent were determined as 6000 r/min for 3 min,and the highest centrifugal survival rate was 91.22%,by determining the survival rate of bacteria under different centrifugation conditions;The optimum conditions for the adsorption immobilization method of aerobic composting composite microbial agent were determined:the best carrier for immobilization was zeolite powder,the carrier addition ratio was 2%（mass fraction）,the immobilization temperature was 50°C,the immobilization time was 8 h,the carrier bacteria absorption amount as the index,through the single factor experiment;The microbial agents prepared by centrifugation and adsorption immobilization were preserved at room temperature.The results showed that the microbial agent with zeolite as the adsorption immobilization material had the best stability,and the survival rate of the microbial agent could still reach 43.36%after 90days of preservation.（2）The drying method used in this experiment was blast drying.The results showed that different drying temperature and drying time had significant effects on the survival rate of bacteria.The optimal drying temperature was 50℃,the optimal drying time was 20 h,and the number of viable bacteria under the optimal conditions was 1.81×10⁸ cfu/g;The different moisture content has a great influence on the preservation effect of immobilized microbial agent.When the moisture content was controlled within 5%～10%,the survival rate after 90 days could be stabilized at about60%;Under the optimum drying conditions,the final moisture content of the microbial agent was 7.18%,which met the conditions of the optimum moisture content.（3）In this experiment,four kinds of protective agents that can effectively improve the survival rate of microorganisms during the drying process were determined,which were peptone（8%）,glycerol（8%）,sodium glutamate（0.4%）and glycine（3%）;The results of L₉（3⁴）orthogonal test showed that the effect of protective agent on the protective effect of microbial agent was as follows:glycine>sodium glutamate>peptone>glycerol.The best formula of compound protective agent was peptone 7%,glycerol 9%,glycine 3.5%,sodium glutamate 0.5%;In this paper,the optimum addition amount of composite protective agent was determined to be 15 m L/g by single factor experiment.The addition amount had little effect on the protective effect of protective agent,and the difference between the maximum and the minimum was only 0.6 orders of magnitude;The optimal p H is 8.0,and p H has a significant impact on the protective effect of the protective agent,The difference between the maximum and the minimum is 1.1 orders of magnitude;The number of viable bacteria in different storage temperature and time was determined in this experiment.The results showed that the lower the temperature,the better the preservation effect of the microbial agent.The preservation effect of microbial agents at-20°C and 4°C was not much different,and the survival rate could reach more than30%after 180 days.The survival rate of the bacteria preserved at room temperature was only about 7%after 180 days.（4）The dynamic changes of microbial community structure that before and after immobilization and different preservation stages of solid microbial agents were analyzed in this study.The result showed that the community structure diversity and richness of the solid microbial inoculant was significantly lower than those of the liquid microbial inoculant.The dominant phylum of the immobilized bacteria was Firmicutes,with a relative abundance of 99.46%.The total relative abundance of Proteobacteria was less than 0.1%,and Bacteroidetes was not detected;The relative abundance of non-spore bacteria in the liquid agent was significantly reduced after immobilization.The dominant genus after immobilization was mainly Bacillus,and its total relative abundance reached more than 80%.It indicated that the survival rate of non-spore bacteria in the immobilized microbial agent was very low,which may be due to the high temperature drying caused a large number of cell death.In non-spore bacteria,the relative abundance of unclassified＿f＿Ruminococcaceae,Lactococcus and Clostridium＿sensu＿stricto＿18 decreased after immobilization,but still greater than 1%,indicating that they have a certain ability to resist adverse external environment;The community structure diversity and richness of solid microbial inoculants gradually increased with time in different preservation stages,but the overall difference was not significant.The specific performance is that the relative abundance of non-spore bacteria gradually decreases during storage,and the relative abundance of Aneurinibacillus and Paenibacillus in spore bacteria is increasing,gradually replacing Fictibacillus,reaching 28.15%and 24.44%respectively after 6months of storage.The relative abundance of Bacillus＿coagulans＿g＿Bacillus decreased during storage,but it was still the dominant strain,and its relative abundance was still 23.88%after 6 months of storage.