Simultaneous Nitrification And Endogenous Denitrification And Phouphorus Removal For Continuous Flow Aerobic Granular Sludge Based On Gradient Influent

The traditional biological nitrogen and phosphorus removal technology has the problems of competition for carbon source among bacteria and low nitrogen and phosphorus removal performance,while simultaneous nitrification and endogenous denitrification and phosphorus removal（SNEDPR）process can strengthen the storage of carbon sources in the anaerobic section,ensure that the subsequent aerobic phosphorus absorption,denitrification phosphorus removal and endogenous denitrification are carried out at the same time,which can effectively solve the competition for carbon sources in the process of denitrification and phosphorus removal.At the same time,the unique spatial structure of aerobic granular sludge（AGS）allows the simultaneous existence of anaerobic,aerobic and anoxic environments,which can maximize the simultaneous nitrogen and phosphorus removal performance of the SNEDPR process.But so far,the stable operation of most AGSs is only achieved in sequencing batch reactors（SBR）,and SBR mostly use fast feeding.Studies have shown that common heterotrophic bacteria with fast feeding can obtain a large amount of external carbon in a short time.Phosphate accumulating organisms（PAOs）and glycogen accumulating organisms（GAOs）cannot store enough internal carbon sources in the anaerobic stage for denitrification and phosphorus removal in the aerobic stage.The slow feeding is helpful to select the slow-growing PAOs and GAOs,but the disadvantage is that the slow feeding continues to inflow with a low substrate concentration,and the rate does not change,so that the inflow stage is in a steady state,resulting in the internal carbon origin store is less responsive.Based on this,this experiment proposes a gradient feeding method,which provides an external carbon source to microorganisms at a non-fixed feeding rate,applies a short-time fast feeding before the slow feeding,and shortens the duration of the slow inflow.,so as to create non-equilibrium growth conditions to improve the internal carbon storage response of granular sludge microorganisms,and optimize operating parameters to enhance the denitrification and phosphorus removal performance of granular sludge,in order to provide theoretical support for actual operation.In order to enhance the internal carbon source storage performance of SBR aerobic granular sludge SNEDPR,the experiments in this chapter focus on the optimization of the influent mode of the SBR aerobic granular sludge process.The flocculent backflow sludge was sent to the SBR reactor,and three inflow modes,gradient feeding,fast feeding and slow feeding,were set up for control experiments,so as to make it clear that the gradient influent in the SBR aerobic granular sludge SNEDPR start-up and internal carbon superiority in source storage.The results showed that the gradient feeding method showed stronger simultaneous nitrogen and phosphorus removal performance,and the average removal of chemical oxygen demand（COD）,total nitrogen（TN）and total phosphorus（TP）The rate reached92.35%,79.07%and 95.87%.The analysis of internal carbon storage characteristics showed that the internal carbon storage rate(COD_in)and SNED rate of gradient influent were higher,which were 99.69%and 81.52%,respectively.At the same time,the biomass of AGS in the gradient inlet water is higher,and the protein content is also higher,so the particle stability is stronger,and the system is more stable.Therefore,the gradient water inflow method improves the internal carbon source storage response of the system,thus obtaining a better internal carbon source storage performance,which can better balance the effect of GAOs endogenous denitrification and denitrification and PAOs using internal carbon source to remove phosphorus.In order to further improve the denitrification and phosphorus removal performance of the system in the treatment of domestic sewage,the second stage of experiments focused on exploring the effect of different anoxic time on the treatment of domestic sewage with gradient influent SBR,and then selecting the appropriate anaerobic/aerobic/deficient oxygen time ratio to enhance the system’s ability to deal with actual domestic sewage.This is because it is difficult for living GAOs to adapt to the complex and changeable carbon source composition,which in turn affects their denitrification and denitrification efficiency,and the A/O/A time ratio formed by suitable anoxic conditions is currently the most reliable way of denitrification.The experiments in this chapter were run in four stages by gradually extending the anoxic time,inoculating the previous stage of granular sludge and adopting gradient water inflow,in order to clearly change the anoxic time to form different A/O/A time ratios for enhanced denitrification and phosphorus removal efficiency.The results showed that when the hypoxia time is 1.5h,the system showed a good performance of simultaneous nitrogen and phosphorus removal under this A/O/A time ratio.The denitrification pathway was dominated by GAOs denitrification,including partial SND（25.24%）and DPAOs denitrification.The ratio of anoxic and phosphorus absorption increased significantly to 2.81%,both denitrification and phosphorus removal and denitrification contributed to nitrogen removal;The rate of phosphorus removal is above 95%,and aerobic phosphorus absorption is the main route of phosphorus removal.Under these conditions,the non-nitrogen and phosphorus removal bacteria were elutriated out of the system,and the MLVSS/MLSS（f）increased to 0.95,and the PN/PS increased to 6.89,which enhanced the particle stability.In order to realize the practical application of the gradient influent aerobic granular sludge SNEDPR process,the third stage of the experiment focuses on the parameter optimization of the gradient feeding continuous flow SNEDPR process to improve the nitrogen and phosphorus removal performance of the continuous flow system and ensure the stability of particles.This is because most of the current continuous flow nitrogen and phosphorus removal performance is low,and the granular sludge system is unstable.In this stage of the experiment,the aerobic granular sludge of the previous stage was inoculated,and the domestic sewage was introduced.On the basis of determining the optimal hydraulic retention time,by exploring different velocity gradients（fast/slow water feeding rates,Q_f:Q_sand fast/slow feeding water duration ratio,T_f:T_s）on the gradient feeding water continuous flow SNEDPR process to determine the optimal operating parameters.The results showed that the optimal HRT required to run the process is 8h,and the system had good stability and denitrification and phosphorus removal performance.The average removal rates of COD,TN and TP are 86.90%,81.48%and 81.49%,respectively.The SVI decreases to 25m L/g,thus ensuring the stability of granular sludge to carry out the next parametric study.When the Q_f:Q_sand T_f:T_sof the system were further changed,when the Q_f:Q_sand T_f:T_sof the system were 3:1 and 2:1,the carbon storage capacity and denitrification,nitrogen and phosphorus removal capacity of the system were significantly improved.The SNED rate and COD_inrate were55.06%and 99.35%,respectively.The proportion of DPAOs in PAOs reached 52.67%.At this time,the average removal rates of COD,TN,and TP reached 86.87%,80.10%and 82.61%.At the same time,when the changes of Q_f:Q_sand T_f:T_shave significantly different effects on EPS and thus affect the particle stability,the effect of increasing Q_f:Q_son EPS content is greater than that of decreasing T_f:T_s,while the effect of increasing Q_f:Q_son EPS content is greater than that of decreasing T_f:T_s.The effect of composition is more significant when T_f:T_swas reduced.