| Based on co-existing of aerobic and anaerobic ammonium oxidizing bacteria in granular sludge, completely autotrophic nitrogen removal process was achieved. Compared to traditional nitration-denitrification process, completely autotrophic nitrogen removal process technology could decrease O2 consuming as much as 60% and hardly consumed COD, which could decrease the energy consuming and the release of CO2 in nitrogen removal process. Through EGSB (Expanded Granular Sludge Bed) reactor starting up, batch experiment in SBR, and observing by microscope, the mechanism of coupling aerobic and anaerobic ammonium oxidizing process was investigated, and by adding trace NO2, the enhancement of NO2 on completely autotrophic nitrogen removal was studied and stimulated, as well as the capabilities of nitrogen removal and the impacts of granules were studied with active carbon added. The results were given as follows:①In a Expanded Granular Sludge Bed (EGSB)reactor, completely autotrophic nitrogen removal granular sludge was cultured inoculating simultaneously aerobic and anaerobic ammonium oxidation bacteria. The pH was controlled between 7.6 and 8.0, DO between 0.6 mg/L and 0.8 mg/L and the up-velocity 4.2m/h. In the end, NH4+-N and TN average removal efficiency was 75% and 52% respectively, TN removal rate reached 0.101 kg/(m3·d).②The effecting of NH4+-N, DO, and pH on the completely autotrophic nitrogen removal performance was investigated in the batch experiments. Aerobic and anaerobic ammonium oxidation rates increased with increasing NH4+-N concentration in a certain range. The much higher DO increased nitrite oxidation rate and inhibited anaerobic ammonium oxidation, and resulted in the lower efficiency of total nitrogen (TN) removal with NO2- and NO3- accumulation in the reactor. The much lower DO decreased aerobic oxidation rate with the less production of NO2-. Anaerobic ammonium oxidation rate and TN removal rate were limited by the lack of NO2-, however, TN removal efficiency was higher with less accumulation of NO2- and NO3- in the reactor. When the concentration of NH4+-N was 60mg/L and DO was 0.40.6mg/L, total nitrogen (TN) removal rate was 27.96 mg/(gMLSS·d) and the TN removal efficiency reached 68%. When pH was 7.8, TN removal efficiency reached the maximum. ③The effect of trace NO2 and kinetic characteristics for coupling of aerobic and anaerobic ammonium oxidation in granular sludge was investigated by batch experiment in SBR. Without O2, the NO2 -dependent ammonia oxidation could be described by the Andrews model. The maximum ammonia oxidation rate was 5.36mg/(g·h). Under trace NO2 atmosphere conditions, aerobic ammonium oxidation was enhanced by increasing the activity of O2 in NOx circulation. When DO was 1.5～2.0mg/L and NO2 was 4.475 mmol/m3, The maximum ammonia oxidation rate was 161.21 mg/(g.h).④The capabilities of nitrogen removal and the impacts of granules were studied with active carbon added. With active carbon, NH4+-N and TN average removal efficiency was 85% and 59% respectively, which rised to 13% compared with without active carbon. And TN removal rate reached 0.10 kg(/m3·d).Without active carbon , the average diameter of granule was 0.5～1.0mm, and with active carbon , the average diameter of granule was 0.8～1.2mm, which increased 33%.
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