| A large amount of nitrate nitrogen wastewater discharge will cause eutrophication of water body and harm human health.Therefore,the removal of nitrate nitrogen from wastewater needs to be solved urgently.Biological denitrification technology is currently the most widely used nitrogen removal method.The key to the efficient denitrification of traditional biological methods is the continuous exposure of wastewater under aerobic and anoxic conditions.However,it is difficult to completely remove the dissolved oxygen(DO)from the wastewater to ensure a strict anoxic environment.The discovery of aerobic denitrification enables nitrification and denitrification to be realized under a single aerobic condition,effectively solving the strict requirements of traditional biological denitrification on anaerobic and anoxic environmental conditions,and has become a current research hotspot.However,even if the aerobic denitrifying bacteria belong to the same genus,their nitrogen removal performance may be different.Therefore,the separation and denitrification performance of aerobic denitrifying bacteria should be further strengthened to provide a theoretical basis for its application in practical wastewater treatment.In this study,an aerobic denitrifying bacteria was isolated and purified from the activated sludge collected in a sewage treatment plant in Taiyuan,named ZYL.Firstly,bacterial species were identified by colony morphology observation,gram staining and 16S rDNA sequence analysis.Secondly,single factor experiment was used to optimize the aerobic denitrification performance of the strain.Then further understood the nitrogen removal performance of strain ZYL from three aspects of nitrogen source utilization,gas production performance and nitrogen balance.Finally,the denitrification pathway of strain ZYL was deduced through the analysis of denitrification key enzyme activity and genes in the process of denitrification of strain ZYL.The main conclusions of this study are as follows:(1)An aerobic denitrifying bacteria was isolated and purified from activated sludge,named ZYL.The strain ZYL was identified by colony morphology observation,Gram staining,and 16S rDNA sequence analysis.The results showed that the strain ZYL belonged to Acinetobacter haemolyticus.(2)Strain ZYL optimum nitrogen conditions: carbon source for sodium succinate,C/N was 20,the initial pH was 7,the temperature of 30 ? and the rotating speed was 120 rpm;The growth of strain ZYL changed little with the increase of initial nitrate concentration,but the degradation efficiency of nitrate decreased gradually.(3)Nitrogen was produced in strain ZYL when it was cultured with nitrate nitrogen,nitrite nitrogen and ammonium as the sole nitrogen sources.The results of nitrogen balance experiments further showed that when nitrate,nitrite and ammonia nitrogen were the sole nitrogen sources,62.23%,62.93% and 64.81% of the initial nitrogen sources were converted to intracellular nitrogen,respectively,accompanied by 34.41%,33.23% The 32.50% nitrogen loss was presumed to have escaped mainly in the form of gaseous nitrogen such as nitrogen,which indicates that the strains could perform aerobic denitrification and heterotrophic nitrification.(4)In the process of nitrate degradation,the nitrate reductase and nitrite reductase activities increased first and then decreased,and the maximum enzyme activity was 0.16 and 0.15 U/mg proteins,respectively.In addition,napA and nirS were successfully amplified from ZYL genome,and the aerobic denitrification performance of ZYL was proved by enzyme activity and gene level.(5)Comprehensive analysis of the aerobic nitrate degradation performance,gas production performance,nitrogen balance results,key enzyme activities and denitrification gene amplification results of strain ZYL,inferred that the removal path of the aerobic nitrate nitrogen of strain ZYL was finally converted into nitrogen through nitrite nitrogen. |
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