| A pilot-scale EGSB-A/O system treating urban sewage was studied in this paper. The process was designed to couple anaerobic ammonium oxidation,methanogenesis and denitrification in EGSB reactor.Experimental methods including physical and chemical indicators,microbial activity,scanning electron microscopy and analysis of microbial community structure were carried out to investigate the characteristics and mechanism of this combined process.After 260 days running,the main results were as fellows:(1) In EGSB-A/O system,the EGSB reactor inoculated with anaerobic granular and activated sludges could fulfill the start-up within 45 days,which was characterised by the simultaneous removal of ammonia nitrogen and nitrite nitrogen.At the beginning,the denitrification and methanogenesis were dominant by the effective conversion of COD and nitrate.During the start-up process,the anaerobic ammonia oxidation was significantly enhanced.The changes of sludge color could indicate the completion of start-up,which turned form black to tan.(2) EGSB-A/O system could effectively deal with the low concentration urban sewage at normal atmospheric temperature.The average concentration of effluent COD,ammonia nitrogen,TN and TP were 34,4.15,13.65 and 0.69 mg/L respectively,which could be achieved the fisrt-class(B) emission standards of urban sewage treatment plants.EGSB reactors had many outstanding advantages such as higher organic removal rates,m ore stability with the changes of environmental and operational conditions,and smaller footpoint.As for A/O,the average removal efficiency of PO43--P and TP were 77.5% and 73.9% respectively.(3) The main factors of EGSB reactor were HRT,influent substrate concentration and organic (volume) loading,reflux ratio,superficial liquid velocity,dissolved oxygen and temperature.We suggested that the HRT and reflux ratio of EGSB reactor be no less than 2 h and no more than 400%.In this study,we found that the adverse effects of dissolved oxygen in its influent could be effectively alleviated.(4) The degree of grey incidence method was applied to analyze the main factors influencing the performance of EGSB reactor.The results showed that superficial liquid velocity was the highest-priority factor among HRT,influent substrate concentration,organic (volume) loading,superficial liquid velocity and temperature.In process control,it was suggested to reasonably adjust the effluent reflux ratio fisrt,followed by the HRT adjustment.(5) The Grau second-order kinetic model and Monod model were applied to the EGSB reactor.Results indicated that the Grau second-order kinetic model was a more appropriate model for describing the kinetic of the EGSB reactor.As a result of the calculation,the kinetic equation for COD and TN degradeation(6) HRT and sludge recycle ratio were the main factors of A/O.Effluent recycle was a important link between EGSB and A/O.Throughout the experiment,the average removal rate ratio of nitrite to ammonia nitrogen was 0.09,while the average removal rate ratio of nitrate nitrogen to ammonia nitrogen was 0.71.EGSB reactor nitrogen removal efficiency increased when the volumetric loading rate ratio of nitrite to ammonia nitrogen was higher,but the volumetric loading rate ratio of nitrate nitrogen to ammonia nitrogen was lower.(7) Promoted by the superficial liquid velocity and organic loading rate,microbial activity such as DHA and PHB detected in EGSB reactor were generally higher than that of A/O.The scanning electron microscopy observation showed that bacteria looked like methanogen was prevailing in anaerobic granular sludge used for inoculation. Some filamentous from activated sludge and ellipsoid bacteria similar to anaerobic ammonium oxidation bacteria were found in EGSB reactor.(8) Analysis of bacterial community indicated that bacteria in EGSB reactor composed of Actinomyces sp.,Acidobacterium sp.,Clostridium sp.,Chloroflexus sp.,Planctomycetes KSU-1,Methanosaeta sp.and Proteobacterium bacteria.The existence of anaerobic ammonium oxidation bacteria,methanogen and denitrifying bacteria was confirmed in the granular sludge from EGSB reactor.lt was proved to be achieved coupled anaerobic ammonium oxidation,methanogenesis and denitrification when treating ubran sewage at normal atmospheric temperature.
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