Development Of Complex Microbial Inoculants And Its Application In Domestic Sewage Treatment

In recent years,with the continuous deepening of the concept of environmental protection,great progress has been made in environmental governance in our country,but there is still the problem of untreated discharge of domestic sewage.The composition of domestic sewage is complex and the pollutant concentration is high,especially COD and NH₄⁺-N,which not only affects the water ecological environment,but even harms human health.Therefore,its efficient treatment is of great significance to the development of the country and the ecological balance of the environment.The specific microorganisms isolated and screened by bioaugmentation technology have the advantages of strong adaptability,rapid reproduction and effective removal of pollutants.Combined with modern molecular biotechnology,the screened microorganisms are prepared into composite microbial inoculants,which can be used for more efficient domestic sewage treatment.By adding complex microbial inoculants,the ability of microorganisms to remove COD and NH₄⁺-N in sewage can be improved,the impact resistance of sewage treatment systems can be improved,and the treatment capacity in low temperature seasons can be improved.In this thesis,a series of experiments were conducted on the development of a complex microbial inoculants for the removal of COD and NH₄⁺-N,and the following results were obtained:（1）Six strains of COD and NH₄⁺-N removal bacteria were isolated from the soil,and species identification was carried out by 16S r DNA sequence analysis,and the species of the strains were determined by Gram staining,physiological biochemical identification and SEM electron microscopy scanning to determine the species of the strains:Bacillus velezensis Y2,Bacillus licheniformis L2 and Yarrowia lipolytica J2;（2）Through a single-variable experiment,the growth environments of three strains of Bacillus velezensis Y2,Bacillus licheniformis L2 and Yarrowia lipolytica J2were changed（medium material,carbon and nitrogen addition,inoculation amount,and fermentation time）,respectively.The suitable fermentation medium conditions of the strain:When the medium raw material of Bacillus velezensis Y2 chose cotton seed meal+sucrose（1:0.1329）5.0 g/100 m L,the inoculation amount was 10⁸CFU/m L and the fermentation time was 6 h,the microbial biomass was the largest;Bacillus licheniformis L2 in the medium raw material was soybean meal+cottonseed meal（0.3689:0.6570）5.0 g/100 m L,the inoculation amount was 10⁹CFU/m L,and the microbial biomass was the largest when the fermentation time was 6 h;The optimum conditions of Yarrowia lipolytica J2 were soybean meal+cottonseed meal（0.3689:0.6570）5.0 g/100 m L,the inoculation amount was 10¹⁰CFU/m L,and the fermentation time was 10 h.（3）The mixture orthogonal test and the optimization combination experiment determined that the formula of the complex microbial inoculants was Bacillus velezensis Y2（3.0%）,Bacillus licheniformis L2（9.0%）,and Yarrowia lipolytica J2（4.5%）;through the investigation of the influencing factors of the purification of artificial domestic sewage by the complex microbial inoculants,the optimal removal conditions were determined to be:2.5%of the bacterial connection,the treatment time was 3 days,and the speed was 120-160 r/min;（4）Under the condition of not using other treatment processes,only simulating treatment in aerobic tanks,the complex microbial inoculants was added to the artificial domestic sewage and the actual domestic sewage to explore its ability to remove COD and NH₄⁺-N,and the results showed that the removal rate of the composite microbial agent on the actual domestic sewage under 30°C was 79.86%and 84.15%,respectively;the composite microbial agent was 79.86%and 84.15%in the actual domestic sewage under 10°C conditions.The removal rates of NH₄⁺-N were 55.22%and 24.01%,respectively,which had a better treatment effect compared with the sewage removal rate without added agents.The complex microbial inoculants developed in this experiment has a certain effect on the treatment of domestic sewage,and provides theoretical guidance for the large-scale production and utilization of fungi in the future.