Study On Combining Endogenous Partial Denitrification With Anammox Process

Anaerobic ammonium oxidation（ANAMMOX）uses anaerobic ammonium oxidation bacteria（An AOB）to oxidize ammonia to nitrogen using nitrite as the electron acceptor.It is the most innovative biological nitrogen removal process so far.At present,ANAMMOX has been widely used to treat high temperature and high ammonia nitrogen wastewater,but there are still shortcomings for mainstream wastewater treatment,and the stable supply of nitrite limits its further development.Endogenous partial denitrification（EPD）is a new method to provide nitrite for ANAMMOX.It consumes organic matter and glycogen in the anaerobic stage and converts them into PHAs.In the anoxic stage,it uses PHAs to synthesize Glycogen and reduces nitrate to nitrite.Therefore,this topic aims to explore the start-up of the EPD-SBR and the factors and mechanisms affecting the nitrate-to-nitrite transformation ratio（NTR）,and explores the potential of coupling two-stage EPD-SBR and ANAMMOX-SBBR to achieve the stability of mainstream anammox process and high-efficiency nitrogen removal.The experimental conclusions are as follows:（1）EPD-SBR was inoculated with return sludge from Xi’an Beishiqiao Wastewater Treatment Plant.Using sodium acetate as the carbon source,controlling the C/P=150:1 of the influent water,and adopting the method of anaerobic waste water to successfully achieve the enrichment of GAOs bacteria;Useing Na NO₃as the electron acceptor,it successfully induced DGAOs,and the total nitrogen removal rate in the system reached more than 98%.When the reaction cycle is 3h,the anaerobic time is 90min,the hypoxia time is 30min,and the C/N ratio is 4.3,the COD removal rate averages 86.74%,and the NTR averaged 65.96%.It proved that the EPD-SBR was successfully started and the EPD effluent can be used as a stable source of nitritefor the ANAMMOX.（2）Experiments on factors affecting nitrite accumulation show that:When the C/N ratio is 6.5,5.2,4.3 and 3.7,the NTR value first increases and then decreases by the C/N ratio continues to decrease.When the C/N ratio is 4.3,the NTR value is the largest,which is66.27%.When the hypoxia time was 20min,30min and 40min,the accumulation of nitrite first increased and then decreased,and the NTR values were 68.05%,66.53%and 48.95%,respectively.When the cycle length is 6h,4h,and 3h,the NTR value is basically the same,with an average of 65.67%,66.07%and 65.24%respectively;when the cycle length is 2h,the nitrate is left in the effluent,and the NTR value also decreases,and the average is 60.49%.When the p H values were 6.88,7.43,7.87,8.45,9.06,the NTR value first decreased and then increased.The NTR value was the lowest at p H 7.87,which was 66.13%,and the highest at p H 9.06,was 70.09%.（3）In the EPD-ANAMMOX process,the ANAMMOX-SBBR is first subjected to 112d low-matrix domestication.The NRR and NRE were 0.337kg/（m³·d）and 79.27%,respectively,of which the nitrogen removal by anammox accounted for 90.03%of the TN removal.In the EPD-ANAMMOX process,COD removal load and removal rate reached 0.337kg COD/（kg MLSS·d）,87.21%;The NRR and NRE were 0.222kg/（m³·d）,85.71%,respectively.As the temperature gradually decreased from 29°C to 14°C,there was no obvious change in the removal rate of COD in the EPD-SBR system（86.59%）,but the activity of DGAOs decreased.Although the NTR value decreased,it could still be maintained at 48.24%～63.48%.On the other hand,the temperature drop has little effect on the ANAMMOX-SBBR,and the average TN removal rate is 86.12%.Experiments show that EPD-SBR provides nitrite stability under normal temperature conditions,and the EPD-ANAMMOX process has broad prospects in the treatment of mainstream wastewater.（4）After the successful domestication of EPD-SBR sludge,the microbial diversity decreased,the number of Proteobacteria increased and the abundance was the highest,71.24%;at the subordinate level,Competibacter GAOs had the highest abundance,25.06%.It is the main function of the internal carbon source short-range denitrification in the EPD-SBR reactor.Moreover,under the limit of phosphorus,the activity of PAOs bacteria is limited,and the abundance of GAOs（25.49%）is much higher than that of PAOs（2.78%）,which proves that the denitrification process of carbon sources in the reactor is mainly carried out by GAOs.