Characteristics Of Nitrate Removal And Auto-aggregation By A Novel Aerobic Denitrifier,Enterobacter Sp.Strain FL

With the rapid development of modern industry and society economy,the problems caused by environmental pollution are becoming more and more serious.Water pollution has become one of the main problems of environmental pollution,and the water body eutrophication caused by the nitrogen imbalance,has become an increasingly important manifestation of water pollution.As a new type of denitrifying functional microorganisms,the aerobic denitrifier provide a new research idea to solve the nitrogen pollution of water body,duo to its tolerance to dissolved oxygen,and its efficient aerobic denitrification capacity.In this study,a strain with aerobic denitrification and auto-aggregation characteristics was isolated from the activated sludge and was identified as Enterobacter sp.and named as Enterobacter sp.FL.Based on the investigation of its aerobic denitrification characteristics,the auto-aggregation characteristics were futher studied.The effect of extracellular polymeric substances(EPS)on the auro-aggregation ability was discussed.Provide some theoretical basis and technical guidance for the practical application of functional microbes with aerobic denitrification and auto-aggregation characteristics.Nitrate was utilized as the sole nitrogen source to study the aerobic denitrification of strain FL.With an initial NO3--N concentration of 100 mg/L,the nitrate and total nitrogen removal efficiency reached 98.9 % and 74.8 %,respectively.N2 was the main nitrogenous gaseous produced bystrain FL.The Nar,Nir enzyme also exhibits a certain activity during the denitrification process.In summary,the speciation of strain FL may be achieved by reducing NO3--N to NO2--N,and then further reducing NO2--N to nitrogen gaseous products such as N2 and N2 O.Meanwhile,strain FL showed the capability of auto-aggregation during the aerobic denitrification process and the morphology of the aggregates were rough,irregular and porous granula.Furthermore,a SBR bioreactor,solely inoculated with strain FL was conducted to assess the feasibility and stability of simultaneous nitrate removal and cells automatic aggregate.During the 16 run cycles,the removal efficiency of NO3--N was maintained at approximately more than 90 %.And the aggregation ability were also kept on range of 35.0 %~41.5 %.The results showed that strain FL hold significant and stable ntrate removal efficiency,and also hold stable auto-aggregation ability,showing great potential application value.The EPS produced by strain FL during the denitrification process and its effect on the auto-aggregation ability was investigated.The results showed that protein and polysaccharide were the main components of EPS.The content of protein was much higher than polysaccharide.Both of these components were reported to be related to the aggregation of microorganisms.During the denitrification process,the auto-aggregation ability of by strain FL was increased with the increase of EPS concentration,the maximum value reached 48.9 %.Whlie the EPS was extracted,the auto-aggregation rate of the cells was significantly decreased and only maintained at 8.0 %.In addition,the investigation of auto-aggregation ability before and after EPS extraction for strain FL after the whole SBR run cycles.And indicated that EPS hold a 22.3 % contribution rate to the aggregation of cells in SBR reactor,and the aggregation rate before and after EPS extraction was 39.2 % and 16.9 %,respectively.This suggested that the EPS produced by strain FL plays an imprtant role of cells auto-aggregatin.The mechanism of the auto-aggregation characteristics of the strain FL by EPS was further investigated.Results showed that the functional groups on the cells surface changed obviously after EPS extraction,and the number of functional groups belonging to the polysaccharide was decreased,moreover,the peak of attributied to the protein amide I region was shifted from 1654 cm-1 to 1648 cm-1.Particularly,the different secondary structures of protein in amide I region were reported to effect the aggregation capacities of microorganisms.In this study,the secondary structure of protein was mainly to promote the cells aggregation before EPS extraction,such as,β-sheets and 3-turn helices with the relative percentage of 49.0 %,31.6 %;respectively.In addition,EPS was also determined to have more than 50 % of the protein secondary structure to promote cell aggregation structure.The studies of EPS distribution showed that the proteins with higher amounts in EPS were evenly and tightly combined to cells.And provide a siginifficant chance for the changes of the secondary structure of proteins.