Study On Preparation And Preservation Effect Of Liquid Denitrification Microbial Agents

Water pollution is a major obstacle that restricts the sustainable development of our country.At present,the urgent problem is to treat the polluted water and prevent the water pollution from getting worse.In view of the high total nitrogen content in urban domestic sewage,adding liquid microbial agents with denitrification effect to sewage treatment system can improve the overall nitrogen removal performance of the system,so as to improve the water environment,and enhance the water restoration and treatment ability.However,how to effectively extend the preservation time of liquid microbial agents and ensure denitrification efficiency are bottleneck problems that limit their wide application.In this study,six denitrification strains,B301（Lysinibacillus fusiformis）,B308（Bacillus mycoides）,B601（Bacillus subtilis）,P6（Bacillus aryabhattai）,X01（Rhizobium pusense）and Y11（Bacillus aerius）were self-screened in the laboratory and mixed in equal proportions to prepare liquid denitrification microbial agent.The liquid denitrification microbial agent was improved through adding foreign aid organic acids,functional strains,and ultrafiltration concentration,respectively,and then preserved.The preparation conditions of the agent were optimized,the preservation methods of the agent were explored,and the practical application effect of the preserved microbial agents on simulated domestic sewage was verified in the MBR（Membrane Bio-Reactor）,aiming to broaden the ideas of microbial agents preservation methods and provide technical support for the large-scale application of microbial agents.The main research contents and results are as follows:（1）Effect of foreign aid acids on the preservation effect of liquid denitrification microbial agents.The liquid denitrification microbial agent was prepared by mixing six strains with denitrification effect self-screened in the laboratory in equal proportion,which showed a better preservation effect after adding 11%（v/v）L-ascorbic acid.After 6 months of preservation under room temperature,sealed and protected from light,the viable bacteria in the microbial agent reached 2.8×10¹⁰CFU,which was 3.7 times that of the control group,and showed a better pollutant removal effect in batch experiments,with 38.1%removal efficiency for total nitrogen,as well as 65.7%COD removal rate.In addition,when the agent was applied to simulated domestic sewage,the removal rates of total nitrogen and COD were23.5%and 60.9%after 48 hours of facultative treatment,and 21.7%and 69.1%respectively after 48 hours of treatment under aerobic conditions.（2）Effect of functional strains on the preservation effect of liquid denitrification microbial agents.The above six strains with denitrification effect were combined with the laboratory self-screened functional strain 2019-04 at the ratio of 1:1:1:1:1:1:2 to a new liquid microbial agent,showing a better preservation effect.After 6 months of preservation under room temperature,sealed and protected from light,the viable bacteria in the agent was2.6×10¹⁰CFU,which was 3.6 times that of the control group,but lower than the viable bacteria in the agent after the addition of foreign aid L-ascorbic acid.In batch experiments,59.7%removal of total nitrogen and 66.8%removal of COD were achieved.In addition,when the agent was applied to simulated domestic sewage,the removal rates of total nitrogen and COD were 23.3%and 75.0%after 48 hours of facultative treatment,and 24.6%and75.0%respectively after 48 hours of treatment under aerobic conditions.（3）Effect of ultrafiltration concentration on the preservation of liquid denitrification microbial agents.The liquid denitrification microbial agent was prepared by using the same six strains with denitrification effect in equal proportions and was concentrated by ultrafiltration at 30 nm membrane pore size,10 times the concentration rate and 0.1 m/s flow rate,which showed a better preservation effect.After 6 months of preservation under room temperature,sealed and protected from light,the survival rate of viable bacteria was 52.6%,which was much higher than the 10.3%of the group without ultrafiltration treatment,but slightly worse than the group with the addition of foreign aid L-ascorbic acid（54.9%）.In batch experiments,the removal rate of total nitrogen was 65.6%,which was 24.8%higher than the control group.In addition,when the agent was applied to simulated domestic sewage,the highest total nitrogen removal rate was 24.4%after 48 hours of facultative treatment,and28.1%after 48 hours of treatment under aerobic conditions.（4）Application research of the improved microbial agent for denitrification effect.According to the above experimental contents,it was found that the addition of foreign aid L-ascorbic acid to the microbial agent was most effective in improving its preservation effect,with the survival rate of viable bacteria after 6 months of preservation（54.9%）better than the addition of functional strains（41.2%）and ultrafiltration concentration treatment（52.6%）,and the research was more economical and convenient.Therefore,the agent preserved for 6months was selected and applied to Anoxic/Aerobic Membrane Bio-Reactor（A/O-MBR）to explore its treatment effect on simulated domestic sewage in the reactor.Comparing the influent and effluent water quality of A/O-MBR,it was found that the experimental group with the microbial agent had excellent nitrogen and COD removal for simulated domestic sewage,with the removal rates of COD and TN ranging from 72.7%to 84.4%and 87.2%to93.1%,respectively,and the highest removal rates were increased by 16.8%and 22.9%respectively compared with the control group.