The Research On Efficiency And Mechanism Of Aerobic Granular Sludge Continious Flow Process For Nitrogen And Phosphorus Removal

With the development of economy,the whole society is faced with overwhelming environmental pressure,especially water pollution.The low carbon economy has become a world consensus,the efficient removal and recycling of pollutions(C,N and P)in wastewater has become a development trend.Aerobic granular sludge(AGS)has attracted much attention because of its advantages such as high sludge concentration,wide tolerance load range,low sludge yield,excellent settling ability and small footprint.However,the difficulty in startup and instability in long-term operation of the aerobic granular sludge continuous flow(AGS-CF)process made it difficult to apply in actual production.In order to solve the above problems and explore stable simultaneous nitrogen and phosphorus removal AGS-CF process,in this study,a continuous flow reactor was constructed,the AGS-CF process start-up method was clarified,and the aeration mode and the intermittent mode were investigated,and the key operating parameters were proposed;on the base of the continuous flow reactor,the internal circulation AGS-CF reactor was developed,and its organic load characteristics and stable operation conditions were explored to realize the simultaneous and efficient removal of nitrogen and phosphorus and the stable operation of the internal circulation AGS-CF process.The structural components and succession laws of archaeal and bacterial communities in a continuous flow system were analyzed by molecular biology methods,meanwhile,the influence mechanism extracellular polymer(EPS),filamentous archaea and filamentous bacteria in aerobic granular sludge on the stability of aerobic granular sludge were clarified.Based on the problem of broken granular sludge in the traditional continuous flow sludge return process,a new type of continuous flow reactor(ACFR)for aerobic granular sludge was developed.Using the method of transferring mature AGS from the sequential batch reactor(SBR)to ACFR and optimizing the sludge retention time(SRT),the AGS-CF process of simultaneous nitrogen and phosphorus removal was successfully started within 30 days.Subsequently,the AGS exhibited good performance of COD and nitrogen removal in ACFR,whose efficiency was above 90.0% and 70.0%,however,the TP removal efficiency could only be 65.0%.The structure of the granules was stable and the volume of discharged sludge had been greatly reduced.After that,the effects of continuous aeration(CA)mode and intermittent aeration(IA)mode were investigated in the AGS-CF process.The IA mode(4 h aeration and 1h non-aeration)could reduce aeration by 20% and improve the performance of AGS-CF process and the settleability of AGS.The time intermittent operation(TIO)mode created by intermittent aeration and the space intermittent operation(SIO)mode created by adding an anaerobic zone had an important impact on the AGS-CF process.The performance of simultaneous nitrogen and phosphorus removal in TIO mode was better than that in SIO mode.The SVI in SIO mode was higher than that in TIO mode.Meanwhile,the PN concentration and PN/PS in SIO were higher than those in TIO.The internal circulation AGS-CF reactor was developed,and the organic load characteristics of the internal circulation AGS-CF process were explored.As the influent COD concentration increased(?400mg/L),the removal efficiencies of TP and TN of aerobic granular sludge increased,reaching 81.8% and 87.2%,respectively,then the simultaneous and efficient removal of nitrogen and phosphorus was realized and the settling of aerobic granular sludge was enhanced;however,when the influent COD concentration increased to 500mg/L,the settling and stability of aerobic granular sludge decreased.In view of the low concentration of easily biodegradable components in domestic wastewater,aerobic granular sludge was easy to lose its stability and other issues.The effect of different HRT on the stability of the internal circulation AGS-CF process under domestic wastewater was studied.With the shortening of HRT,the performance decreased,the settling ability and stability of granules decreased,the removal efficiencies of COD,TP and TN decreased from 90.2%,82.6% and 83.0% when HRT was 9h to 80.5%,39.6% and41.4% when HRT was 4.5h;the increase of filamentous bacteria on the surface of aerobic granular sludge led to the decrease of its settling and stability and the concentration of EPS increased,especially PN content.High-throughput sequencing technology was used to analyze the microbial community of aerobic granular sludge.The result showed that the predominant archaeal and bacterial genus were ammonia oxidizing archaea(AOA)Nitrososphaera and denitrifying polyphosphate-accumulating organisms(DPAOs)Pseudomonas within AGS-CF process.Methanogenic archaea(MA),AOA,denitrifying bacteria(DNB)and DPAOs played an important role in the removal of nutrients in AGS-CF process.In the internal circulation AGS-CF process,the filamentous archaea Methanothrix had a competitive advantage over filamentous bacteria Thiothrix with high COD concentration,meanwhile,the abundance of both filamentous Methanothrix and Thiothrix were closely related to SVI,granular integrity coefficient(GIC)and EPS of SNDPR granules.Besides,the increase of filamentous Methanothrix and Thiothrix at short HRT led to the increase of EPS and SVI,and the effect of Thiothrix on granule settling was greater than Methanothrix.Based on the above results,a granular ecological model was proposed to elucidate the simultaneous nitrogen and phosphorus removal and the stability of granules,and the inner relationship between the microbial community.The research results of this paper will be of great significance to the practical application of the AGS-CF process.