Research On Removal Of Nitrogen And Phosphorus And Characteristics Of N₂O And NO Productions Under Simultaneous Nitrification And Denitrification

Simultaneous nitrification-denitrification and phosphorus removal（SNDPR）has attracted wide attention due to its advantages of low energy consumption,good treatment effect and carbon source saving.However,the sludge age contradiction with polyphosphaste-accumulating organisms,heterotrophic denitrifying bacteria and denitrifying bacteria are different.It is often difficult to achieve good results of biological nitrogen and phosphorus removal at the same time.Therefore,it is necessary to study how to achieve good removal effect of nitrogen and phosphorus in SNDPR process.Secondly,N₂O and NO do great harm to the environment,and biological nitrogen removal of sewage is one of its important sources.Therefore,it is necessary to study the production characteristics and mechanism of N₂O and NO in SNDPR process.Using Anaerobic/Aerobic/Anoxic-Sequencing Batch Reactor（An/O/A–SBR）,and set the DO automatic monitoring device of precise control of ammonia oxidation process,control the DO concentration to achieve partial nitrification and stop aeration at the end of NH₄⁺-N oxidation to achieve a good and stable SNDPR effect.In order to strengthen phosphorus removal effect,side-stream enhanced phosphorus removal technology was adopted.In other words,during the stable phase of SNDPR denitrification effect,sodium acetate（CH₃COONa）was added to the influent to enhance anaerobic phosphorus release and the phosphorus-rich supernatant was discharged for chemical treatment,and then returned to the mainstream reactor for further biochemical treatment.When approaching the discharge standard,carry out side-stream enhanced phosphorus removal technology again to achieve effluent TP standard;The experimental control of DO concentration was 0.15、0.2 and 0.25 mg·L^-1,respectively.To explore the effects of different DO concentrations on the denitrification and dephosphorization of SNDPR.The controlled influent C/N was 10、7 and 5,respectively.To explore the mechanism of SNDPR denitrification and phosphorus removal under different C/N conditions,as well as the release characteristics and mechanism of N₂O and NO.（1）Under the condition of C/N=7,PO₄^3--P=5 mg·L^-1,the side-stream phosphorus removal achieved good results.Two side-stream enhanced phosphorus removal were carried out.The results showed that the concentration of PO₄^3--P in effluent was less than 0.5 mg·L^-1 after enhanced phosphorus removal,and two times enhanced lasted for2 and 16 days respectively.The average removal rates of PO₄^3--P were 95.83±0%and96.67±3.7%,respectively.the cumulative dephosphorization was 22.2mg and 519.1mg,respectively.When the effect of enhanced phosphorus effect will disappears,it is usually accompanied by a decrease in the release of anaerobic PO₄^3--P.Therefore,when the release of anaerobic PO₄^3--P<4mg·L^-1,side-stream enhanced phosphorus removal can be performed again.（2）The experiment has proved the importance of selecting the appropriate DO concentration.When operating at a moderate DO concentration(0.2mg·L^-1),the ammonia-oxidation rate is close to the heterotrophic denitrifying bacteria rate.At the end of the aerobic stage,the accumulation of NO_x^--N is the minimum,The nitrogen removal time is the shortest,the nitrogen removal efficiency is the highest,and the phosphorus removal efficiency can reach 100%.（3）In the aerobic phase,The concentration of NH₄⁺-N decreased in two stages,while the concentration of TN decreased in three stages.At the initial stage of aeration,aerobic phosphorus accumulation was dominant,which inhibited the oxidation of NH₄⁺-N.The decline rate of NH₄⁺-N and TN was slow and consistent;When the PO₄^3--P concentration decreased to 0mg·L^-1,the nitrification rate was greater than the denitrification rate,the removal rate of TN was slower;With the operation of the reactor,the ammonia oxidation rate increases significantly,and the NH₄⁺-N and TN decline rates become faster.（4）Under different C/N conditions,the production laws of N₂O and NO are basically the same.With the increase of C/N,the total production of N₂O and NO also increased.The total production of N₂O was 1.93 mg·L^-1,1.94 mg·L^-1 and 2.59 mg·L^-1,respectively.The total production of NO was 0.26 mg·L^-1,0.3 mg·L^-1 and 0.44 mg·L^-1,respectively.（5）After the side-stream phosphorus removal（C/N=7）,the microbial diversity was increased,The abundance of PAOs increased from 5.14%to 6.6%.The high C/N ratio（C/N=10）operation leads to the proliferation of GAOs.Candidatus＿Competibacte accounting for 34.5%.Nitrospira is a key bacterium for the accumulation of NO₃^--N in aerobic stage.With the operation of the reactor,the abundance of Nitrospira decreased from 0.99%to 0%.