Investigation Of The Nitrogen And Carbon Removal Using Aerobic Denitrifying Actinobacteria

With the acceleration of urbanization,urban and rural surface waters are subject to different degrees of nitrogen pollution,such as source reservoirs and landscape waters,which are usually micro-polluted,which has potential risks to eutrophication and water quality degradation.Microbial aerobic denitrification has become a hot spot for biological denitrification due to its strong dissolved oxygen resistance,cost-effectiveness,and clean by-products.In addition,aerobic denitrification can solve the problem that anaerobic denitrification in natural aerobic aquatic ecosystems such as lake reservoirs is difficult to carry out.Therefore,it is of great significance to screen out microorganisms with aerobic denitrification ability.Actinomycetes are environmentally adaptable microorganisms that can proliferate by producing asexual spores and by bacterial body rupture and can also produce a wide range of hydrolytic enzymes and secondary metabolites to degrade complex organic matter.However,how to screen out actinomycetes with aerobic denitrification capacity has been rarely reported.In this study,three mixed-culture aerobic denitrification actinomycetes（Mix-CADA）and three high-efficiency aerobic denitrification actinomycetes strains were screened from overlying water samples of different landscape water bodies,and two actinomycetes with general aerobic denitrification ability were co-cultured,and their denitrification and carbon removal characteristics and their application in micro-polluted raw water treatment were explored respectively,in order to provide a theoretical basis for the bioremediation of actinomycetes on micro-polluted water.The main results of this study are as follows:（1）Characteristics of nitrogen and carbon removal of aerobic denitrification actinomycetes and application of raw water.Three highly efficient mixed cultures of aerobic denitrifying actinomycetes Y23,X21 and Y27 were screened from overlying water samples of different landscape water bodies,and their removal rates of nitrate（NO₃^--N）in low-nutrient denitrification medium were 98.32%,97.19%and 98.56%,respectively.The removal rates of total nitrogen（TN）were 96.67%,96.85%and 98.05%,respectively.The removal rates of dissolved organic carbon（DOC）were 92.97%,90.71%and 90.85%,respectively.The results of nitrogen balance analysis showed that the three flora could convert about 79.00%,81.08%and79.54%of the initial nitrate into gaseous nitrogen products,respectively.Illumina Mi Seq sequencing showed that Streptomyces sp.was the dominant genus among the three flora.The results of the network analysis showed that Streptomyces exfoliates were the core species for the removal of DOC and TN in the three flora.The results of raw water experiments showed that the removal rates of TN in the raw water of the three micro-polluted water were 81.86%,78.29%and 80.74%,respectively.The removal rates of permanganate index(COD _Mn)were 63.13%,60.09%and 70.18%,respectively,and the three flora could use humus in raw water,and Y27 could also use aromatic proteins and soluble microbial byproducts.（2）Denitrification performance of aerobic denitrifying actinomycetes strains and remediation of micro-polluted water.Three strains of aerobic denitrification actinomyces with efficient nitrogen removal and carburization capabilities were screened,all of which were identified as Streptomyces sp.,named Streptomyces venezuelae D18,Streptomyces phaeofaciens LST24 and Streptomyces luteogriseus Ed30.The NO₃^--N removal rates in low-nutrient denitrification medium were 99.79%,99.12%and 98.98%,respectively.The TN removal rates were98.44%,97.18%and 97.08%,respectively.The DOC removal rates were 93.34%,91.50%and 90.71%,respectively.The results of nitrogen balance analysis showed that the three strains could convert about 78.36%,79.69%and 78.69%of the initial nitrate into gaseous nitrogen products,respectively.The results of univariate experiments showed that the optimal conditions for NO₃^--N removal by the three strains were C/N=10,speed 135rmp and p H=7,the best carbon source for NO₃^--N removal by strains D18 and LST24 was soluble starch,while the best carbon source for NO₃^--N removal by strain Ed30 was glucose.The results of raw water experiments showed that the TN removal rate of the three strains in the raw water of micro-polluted urban landscape water could reach up to88.02%.The removal rate of COD _Mn was up to 91.76%,and the removal rate of TN from the raw water of the micro-polluted water source reservoir by three strains was up to80.25%.The COD _Mnremoval rate can reach up to 81.12%,and all three strains can use humusoids,aromatic proteins and soluble microbial by-products in raw water for aerobic denitrification.（3）Co-culture of aerobic denitrifying actinomycetes to strengthen the nitrogen removal mechanism and urban lake treatment.Two strains of Actinomyces with average aerobic denitrification performance were screened,both of which were identified as Streptomyces sp.PYX97 and Streptomyces sp.TSJ96.The TN removal rates in low-nutrient denitrification medium were 35.58%and47.51%,respectively.The DOC removal rates were 39.63%and 56.82%,respectively.The co-culture strains PYX97 and TSJ96 under aerobic conditions could stimulate the nitrogen and carburization ability of the system,and the co-culture system could increase the TN removal rate to 95.04%and the DOC removal rate to 92.13%.In addition,compared with the single-culture co-culture system of strains,the concentration of adenosine triphosphate was significantly increased by 3.2 times,and the activity of the electron transport system was increased by 2.7 times.The results of single-factor experiments showed that the optimal conditions for removing NO₃^--N in the co-culture system were C/N=10,speed 150 rpm and p H=7.The results of Biolog analysis showed that co-culture had good carbon source metabolic activity（especially for amines and carboxylic acids）compared to single cultures.The results of raw water experiments showed that the TN removal rate of the two strains in the raw water of the micro-polluted urban lake could reach up to 37.65%.The removal rate of COD _Mn can reach up to 35.60%,while the co-culture system can increase the removal rate of TN and COD _Mn to 83.31%and 84.37%,in addition,the humic acid in the raw water can hardly be used by the strain under a single culture,and the co-culture system can not only degrade the humic acid in the raw water,but also degrade aromatic proteins and soluble microbial byproducts in the metabolic process.