Nitrogen Removal Characteristics For Aerobic Denitrifying Communities And Its Mechanism Of Inorganic Electron Donor Enhancement

Urban lakes are an important part of urban water systems and play an important role in the ecological service functions of cities and in the construction of urban development.However,the high-speed driven development of urban modernization has increased the demand for the ecological services of urban water systems,which can undermine the fragile ecological functions of urban lakes.Excessive nitrogen inputs from climate change and anthropogenic activities have allowed urban lakes to carry large amounts of nitrogenous material,causing a range of environmental problems in urban lakes,such as water quality deterioration and eutrophication.Compared to physical-chemical methods,biological methods have been widely used by researchers in water ecosystems for their low cost,high efficiency,and green sustainability in nitrogen treatment.Aerobic denitrification has become an extremely important research topic due to the ability of aerobic denitrifying microorganisms to denitrify in urban lake ecosystems as opposed to traditional anaerobic denitrification.Moreover,compared to aerobic denitrification monocultures,aerobic denitrification flora have the advantages of short isolation times and resistance to unfavorable water conditions.The main limiting factor of nitrogen pollution control in water body is the lack of enough electron donors to maintain the function of denitrifying microorganisms.Adding inorganic electron donors can effectively improve the aerobic denitrification capacity of nitrogen-polluted water.In this study,highly efficient mix-cultured aerobic denitrifying microbial communities were screened out from urban lake sediments.The nitrogen removal characteristics,core species dynamics and optimal denitrification conditions of aerobic denitrifying microbial communities were investigated;aerobic denitrifying microbial communities were used to treat nitrogen pollution in the urban lakes;the response mechanism of inorganic electron donors to promote the biodegradation of indigenous functional microorganisms and the dynamic changes of microbial communities were investigated.The specific results of this study are as follows:(1)Scanty attention has been paid to augmenting the denitrification performance of polluted lake water by adding mix-cultured aerobic denitrifying bacterial communities(Mix-CADBCs).In this study,to solve the serious problem of nitrogen pollution in lake water bodies,aerobic denitrifying bacteria were added to lake water to enhance the nitrogen and carbon removal ability.Three Mix-CADBCs were isolated from lake water and they could remove more than 94% of total nitrogen(TN)and dissolved organic carbon,respectively.The balance of nitrogen analysis shown that more than 70% of the initial nitrogen was converted to gaseous nitrogen,and less than 11% of the initial nitrogen was converted into microbial biomass.The batch experiments indicated that three Mix-CADBCs could perform denitrification under various conditions.According to the results of nir S-type sequencing,the Hydrogenophaga sp.,Prosthecomicrobium sp.,and Pseudomonas sp.were dominated genera of three Mix-CADBCs.The analysis of network indicated Pseudomonas I.Bh25.14 and Vogsella LIG4 were correlated with the removal of TN and dissolved organic carbon in the Mix-CADBCs.Compared with lake raw water,the addition of three Mix-CADBCs could promote the denitrification capacity(the removal efficiencies of TN > 78.72%),microbial growth(optical density increased by 0.015-0.138 and the total cell count increased by 2 times),and organic degradation ability(the removal efficiency chemical oxygen demand > 38%)of lake water.In general,the findings of this study demonstrated that Mix-CADBCs could provide a new perspective for biological treatment lake water body.(2)Less attention focused on the nitrogen removal performance of mixed-culture aerobic denitrifying fungal flora(Mix-CADFF)in the low C/N polluted water bodies.In this study,three Mix-CADFF were separated from urban lake overlying water.The total nitrogen(TN)removal efficiencies were 93.60%,94.64%,and 95.18%,respectively for Mix-CADFF LN3,LN7,and LN15.Meanwhile,the dissolved organic carbon removal efficiencies were 96.64%,95.12%,and 96.70%,respectively for Mix-CADFF LN3,LN7,and LN15.Three Mix-CADFFs could utilize diverse types of low molecular weight carbon sources to drive the aerobic denitrification processes efficiently.Meanwhile,even the optimal aerobic denitrification performance of three Mix-CADFFs was C/N = 10,which could reduce more than 86.27% of nitrate under C/N = 2 conditions.The highthroughput sequencing analysis of three Mix-CADFFs based on ITS specific primer indicated that Eurotiomycetes,Cystobasidiomycetes,and Sordariomycetes were the dominant phylum of three Mix-CADFFs.The network analysis presented that the rare species(Scedosporium dehoogii,Saitozyma,and Candida intermedia)presented positive co-occurrence with the TN and organic matter removal.Immobilization Mix-CADFFs treatment raw water experiments indicated that three Mix-CADFFs could reduce more than 27.72%,and 62.73% of TN,respectively for oligotrophic reservoir water and urban lake water.Meanwhile,the cell density and cell metabolism indexes were also increased during the raw water treatment.This study will provide new insight into the resource utilization for the mixed-culture aerobic denitrifying fungal community in the environment reparation field.(3)The denitrification capacity of native microorganisms was enhanced with inorganic electronic donors(IE)to treat urban lakes water.The concentrations of nitrogen and organic matter were significantly reduced in the system with IE compared to the system without IE,indicating that IE promotes the physical and chemical removal of pollutants.There was a significant increase in the total cell count and ATP content of the IE-added compared to without IE.Multivariate statistical analyses such as redundancy analysis(RDA)and network analysis(Network)were used to show that the treatment group with IE had the most significant effect on the regulation of bacterial and fungal population structure,and the population structure was more strongly correlated with TN concentration.In addition,high-throughput sequencing showed that microbial population structure and interactions were altered by the addition of IE,which facilitated the transformation and reduction of pollutants.Microbial functions,such as pollutant removal and expression of functional enzymes responsible for the conversion of nitrate nitrogen to ammonia,are highly effective in IE systems.This study provides an innovative strategy for enhancing in situ remediation of micro-pollutants water bodies.