Low-carbon Nitrogen Removal Based On Partial Nitrification Of Zeolie Sequencing Batch Reactor

It is a big challenge to realize the low-carbon and economical nitrogen removal for wastewater treatment.The traditional denitrification technology could not deal with the wastewater of low C/N ratio.According to the characteristics of this kind wastewater,nitrogen removal based on partial nitrification of zeolite SBR-anammox coupling denitrification process could not only remove organic matter,the nitrogen removal efficiency of the whole process could be improved at the same time.However,how to achieve stable partial nitrification and control the effect of organic on the anammox coupling denitrification,was the two technical difficulties in this study.Under laboratory conditions,SBR filled with zeolite and the up flow blanket filter bed?UBF?were used to start partial nitrification and anammox coupling denitrification,respectively.This study intended to explore the operation control strategy of each reactor and the corresponding microbial characteristics,then the two-stage reactor was connected for low C/N wastewater treatment and the nitrogen removal efficiency,process conditions were also studied.Therefore,this study tried to support theoretical basis for the application of the integrated nitrogen removal process.Firstly,based on the ammonium adsorption of zeolite,the feasibility and mechanism of partial nitrification of SBR filled with zeolite was investigated.Then,the effect of alkalinity ratio,adsorption capacity of ammonium and C/N ratio on partial nitrification were investigated.Because of the adsorption and desorption equilibrium of zeolite,it maintained a level of ammonium concentration in the reactor,so an appropriate free ammonia?FA?concentration could also obtained.Through control FA concentration,ammonia oxidizing bacteria?AOB?were enriched,and nitrite oxidizing bacteria?NOB?were selective inhibited,so the stable partial nitrification was finally achieved.The results of single factor experiment showed that,the highest nitrite production rate?NPR?of 1.1 kgN/?m³·d?in the reactor was attained when the alkalinity ratio was 5:1;the larger of the ammonium adsorption capacity on zeolite,the larger NPR and higher nitrite concentration could obtained;the effect of low concentration organics on partial nitrification was not obvious under sufficient dissolved oxygen;High-throughput sequencing analysis results further presented that the reactor had higher relative abundance average of AOB in genus level,and the relative abundance of NOB was almost undetectable,which were in favor of better partial nitrification.Next,UBF enriched with anammox was treated with organic matter,and the effect of C/N ratio on nitrogen removal via anammox coupling denitrification by gradually increasing the concentration of COD in the influent was investigated,combined with thermodynamics,the gibbs free energy(?^?₈))of each reaction in the coupled system were analyzed.The results showed that when the C/N ratio was 2.5,the highest nitrogen removal efficiency could obtain,and the total nitrogen?TN?removal rate was 96%;under this stage,the?^?₈)of anammox was less than that in denitrification reaction,so the occurrence of anammox was prior to the denitrification with 75.8%contribution rate to nitrogen removal.When the C/N ratio increased to 3.5,TN removal rate decreased,and the?^?₈)of anammox began to rise and higher than that in denitrification,therefore,denitrification became the dominant.High-throughput sequencing analysis and qPCR results further demonstrated that the anammox and denitrifying bacterium could be coexisting in the same reactor;when C/N ratio was 2.5,the amount of anammox was the highest among the other influent C/N ratio,and the amount was 1.58×107copies/ul DNA.Finally,the SBR filled with zeolite was operated for 25 days to make the effluent meet the influent requirement of anammox coupling denitrification.On the 26^th day,the two-stage reactor was connected,and the denitrification performance of the combined process for treatment of low C/N ratio was studied.The results indicated that the effluent concentration of ammonium and COD was 2 mg/L and 41 mg/L,while the influent concentration was about 300 mg/L and 600 mg/L,respectively.The main denitrification and carbon removal were carried out in UBF,the corresponding removal rate of TN and COD in UBF was66.5±4.5%and 71.8±4.9%,respectively.