Aerobic granules,as self-aggregated bio-particles by microorganisms under certain selection pressures,have compact structure and good settling ability.It is believed that aerobic granulation would be a novel and promised biotechnology for simultaneous removal of COD,N and P in wastewater treatment.In this study,aerobic nitrifying granules were successfully cultivated under stepwise increased selection pressure.Aerobic nitrifying granules,which were enriched with nitrifying bacteria,had excellent stability and were able to simultaneous organic oxidation,nitrification,and partial denitrification.This study detailed investigated the cultivation,storage,and disintegration process of aerobic nitrifying granules, the self-remediation behaviors after granule storage and disintegration,and the feasibility in synthetic high ammonia-nitrogen catalytic wastewater treatment.The main experimental results were listed as follows:(1) This study evaluated the utility of a cultivation strategy of stepwise increased selection pressure for aerobic granulation and investigated the performance of aerobic nitrifying granules.Results showed that aerobic granules failed to be developed under substrate NH_4~+-N of 200 mg/L.Heterotrophs dominated aerobic granules formed under substrate NH_4~+-N of 50 mg/L were fluffy structured and unstable due to the outgrowth of filamentous bacteria and they were quickly disintegrated from day 131.Nitrifying bacteria were gradually selected and enriched in aerobic granules by adopted a cultivation strategy of stepwise increased substrate NH_4~+-N from 50 to 200 mg/L.Finally,aerobic nitrifying granules capable of simultaneous organic oxidation,nitrification,and partial denitrification, were successfully formed.This cultivation strategy stepwise improved the performance of aerobic nitrifying granules,such as MLSS,granules size,settleability,and nitrifying and denitrifying activities.Enrichment of nitrifying bacteria also suppressed filamentous growth and further improved the stability of aerobic nitrifying granules.During 283 days' operation, no evidence of granule disintegration could be found.The respective COD,NH_4~+-N,and total nitrogen(TN) removal efficiency reached 82%,98%,and 50%when the substrate COD and NH_4~+-N concentration were 500 and 200 mg/L,respectively.(2) A short-term storage of 2 months on the performance of aerobic nitrifying granules and the effect of operational conditions on the reactivation of nitrifying bacteria were investigated.The physical characteristics and structure stability of aerobic nitrifying granules had not significantly changed after short-term storage.At shear force of 0.9 cm/s and cycle time of 4 h,heterotrophs reactivated quickly and the COD removal efficiency recovered and stabilized above 80%after 5 days.While the respective specific oxygen utilization rate (SOUR) of AOB and NOB recovered 88%and 82%as that of before storage and the NH_4~+-N removal efficiency was only between 80%～90%.When the shear force was increased to 1.8 cm/s on day 41,AOB was fully recovered and NH_4~+-N removal efficiency reached above 98%,while the activity of NOB recovered only 92%during this period.Until day 65 when the cycle time was prolonged to 6 h,NOB was fully reactivated.(3) The evolution of physical characteristics,structure,and population decay of aerobic nitrifying granules during a long-term storage of 7 months and the self-bioremediation behavior after storage were investigated.Some cavities and pleats appeared on the surface of granules after storage.Meanwhile,the ratio of VSS/SS decreased and the settleability was also deteriorated.However,the structure stability of aerobic nitrifying granules was remained. During storage,though both heterotrophs and nitrifying bacteria significantly decayed, nitrifying bacteria decayed slower.Microorganisms firstly used extracellular polymeric substances(EPS) as substrate and residual oxygen as electron acceptor after storage began, and then produced more and more EPS during the rest storage,in particular polysaccharides (PS).The slower decay rate of nitrifying bacteria and the production of EPS would be two important reasons for maintaining structural stability of aerobic nitrifying granules during long-term storage.During self-remediation period,the physical characteristics and microbial activities of aerobic nitrifying granules were quickly recovered.After one month,their structure,VSS content,and settleability were both reactivated and even became better.Under shear force of 1.8 cm/s and cycle time of 6 h,heterotrophs and nitrifying bacteria can by fully recovered within 16 and 11 days,respectively.(4) This study described the detailed disintegration mechanism of aerobic nitrifying granules.Along with the increase of granule size,the ultimate reason for disintegration of aerobic nitrifying granules was mass transfer limitation of substrates and dissolved oxygen (DO).The detailed disintegration process can be concluded as follows.Firstly,granules exhibited distinct void structure because the channels presented within granules were eventually plugged and cavity structure in the center of granules was enlarged.Secondly,gas produced by denitrification and anaerobic fermentation came into being pressures within granules and further led to appearance of fissures on the granular shells.Finally,fragments broken off and granules were completely disintegrated.(5) The feasibility of adding fresh activated sludge for stimulating self-remediation of disintegrated granules was evaluated in this study.Results showed that fresh activated sludge was gradually adsorbed into disintegrated and cavity granules and then combined together with granules.Disintegrated aerobic granules were fully remedied after about 3 weeks. Remedied granules exhibited regular and compact structure.Granule settleability and strength were both improved profoundly during self-remediation.Besides those activated sludge used for bioremediation,the rest formed fresh aerobic granules finally.Reactor system which was composed of bioremedied and fresh granules exhibited excellent performance.The respective removal efficiency of COD,NH_4~+-N and TN were stabilized at about 90%,99%and 50% when the substrate COD and NH_4~+-N concentration were 500 mg/L and 150 mg/L, respectively.(6) This study also investigated and confirmed the feasibility of aerobic nitrifying granules in synthetic high ammonia-nitrogen catalytic wastewater treatment.At cycle time of 4 h and NH_4~+-N concentration of 600 mg/L,the wolumetric load of NH_4~+-N achieved 1.8 kg/m~3·d and the NH_4~+-N removal efficiency exceeded 98%.The system had a high capacity in resistance to shock loading.The removal efficiency of COD was about 75%to 90%when the COD concentration was fluctuated between 100 mg/L and 400 mg/L.When the NH_4~+-N concentration was fluctuated between 300 mg/L and 600 mg/L,NH_4~+-N removal efficiency was basically above 97%.The effluent reached the first class integrated wastewater discharge standard(GB 8978-1996).