| One-stage completely autotrophic nitrogen removal process could realize the conversion of ammonium to denitrogen gas by autotrophic bacteria in one reactor, and it has remarkable potential to treat low C/N ratio wastewaters. Many problems of the control method and mechanism of the process have not been well resolved, which restrict its application of the process in engineering. In this paper, the rapid start-up methods of one-stage completely autotrophic nitrogen removal system were studied , the influencing mechanism of control factors and suitable combination work conditions of the process were discussed , in addition, comparing the characteristics of one-stage autotrophic nitrogen removal of biofilm and suspended sludge in the system, the sludge form playing dominant roles in nitrogen removal was analyzed, and the nitrogen balance and the NH4+ conversion pathways were studied in depth.Four SBBRs (Sequence Batch Biofilm Reactors) were employed to start up one-stage completely autotrophic nitrogen removal system and proper conditions and methods of setting up the system were studied, results showed that: (1) The start up process could be divided into two periods. In the first period NO2- accumulation rate was high but nitrogen removal efficiency was low. In the second period, NH4+ was converted quickly and there was little accumulation of NO2- and NO3-, with increasing efficiency of nitrogen removal in the system. (2) Both intermittent aeration mode and continuous aeration mode could be used for starting up one-stage completely autotrophic nitrogen removal system, but higher DO concentration (Dissolved Oxygen) was needed in the intermittently aerated system. (3) Too high DO concentrations (higher than 1.5mg/L in continuous aeration mode) could result in aerobic NO2- oxidation in the whole process, which was not good for the start up of one-stage completely autotrophic nitrogen removal system. However, too low DO concentration (lower than 0.8mg/L in continuous aeration mode) could extend the start-up time. (4) HRT (Hydraulic Retention Time) of one-stage completely autotrophic nitrogen removal system should be determined by"elevation point"of DO and NO3- concentrations in one operation cycle, and adjusted with aeration mode and DO concentration of the system. (5) Both soft combination packing and elastic solid packing were more beneficial for rapid biofilm attachment than globular packing, and soft combination packing was more useful for biofilm adherence and stable operation of one-stage completely autotrophic nitrogen removal system than elastic solid packing. (6) Functioning bacteria in the system was identified through T-A cloning. Two sequences of AOB, one sequences of NOB and eleven sequences of AAOB were found in the system.Conditions of the SBBR one-stage completely autotrophic nitrogen removal system were adjusted to study the influence of aeration mode, DO concentration, temperature and pH and the optimal combination work conditions of the system. Results indicated that nitrogen removal efficiency could be improved in intermittent aeration mode when aeration time was equal to non-aeration time in one aeration cycle; Too high DO concentration could reduce the nitrification reaction rate, which led to relatively low ANAMMOX (Anaerobic Ammonium Oxidation) reaction rate and the poor performance of one-stage autotrophic nitrogen removal system. However, too high DO concentration could damage the anaerobic zone in the biofilm, reduce ANAMMOX reaction rate, and the remaining NO2- could be further oxidized to NO3-, which was not conducive to the effective removal of NH4+; DO concentration should be adjusted according to aeration mode of the system. The optimal DO concentrations of the one-stage completely autotrophic nitrogen removal system in intermittent aeration mode (with aeration/non-aeration ratio of 2h: 2h) and continuous aeration mode were 2.0mg/L and 1.5mg/L, respectively. The optimal temperature of intermittent aeration mode SBBR one-stage autotrophic nitrogen removal system was 30℃. The increased temperature (not higher than 30℃) would improve ammonium conversion and nitrogen removal efficiency. But when temperature reached 35℃, reaction rate of ANAMMOX was too low to convert NO2-, which come from nitrification to N2 thoroughly, under the condition of 2.0mg/L of DO concentration, part of NH4+ was oxidized to NO3- through nitrification. With pH=8, the reaction rate of nitrification and ANAMMOX increased, and would be equivalent, which was helpful for combination nitrogen removal of nitrification and ANAMMOX, thus one-stage autotrophic nitrogen removal performed very well.Taking the biofilm (including biofilm on the packing and biofilm on the reactor inner wall) and suspended sludge in one-stage completely autotrophic nitrogen removal system as the research objects, the nitrification of the biofilm and suspended sludge, aerobic NO2- oxidation, AMAMMOX reaction and one-stage completely autotrophic nitrogen removal activity were investigated. And the causes of the denitrification differences and the dominant sludge playing roles in nitrogen removal were in depth analyzed, by comparing the autotrophic denitrification activity of biofilm and suspended sludge. Results showed that nitrification activity, ANAMMOX activity, aerobic NO2- oxidation activity and one-stage completely autotrophic nitrogen removal activity of biofilm on the packing were 0.153±0.0064 gN·gVSS-1·d-1, 0.0087±0.0016 gN·gVSS-1·d-1, 0.282±0.0086 gN·gVSS-1·d-1 and 0.207±0.0045 gN·gVSS-1·d-1, respectively, and that of biofilm on the reactor inner wall were 0.167±0.0087 gN·gVSS-1·d-1, 0.0045±0.0016 gN·gVSS-1·d-1, 0.313±0.014 gN·gVSS-1·d-1 and 0.298±0.0060 gN·gVSS-1·d-1, respectively, and that of suspended sludge were 0.137±0.0080 gN·gVSS-1·d-1, 0.045±0.0038 gN·gVSS-1·d-1, 0.095±0.0052 gN·gVSS-1·d-1 and 0.099±0.011gN·gVSS-1·d-1, respectively. Nitrification activity, ANAMMOX activity and one-stage completely autotrophic nitrogen removal activity of two kinds of biofilm were higher than that of suspended sludge, but aerobic NO2- oxidation activity of biofilm were lower than that of suspended sludge, which indicate that biofilm is more beneficial for the formation of aerobic-anaerobic micro-environment to make nitrification and ANAMMOX reaction perform well, and biofilm played dominant parts in one-stage completely autotrophic nitrogen removal system.The varieties and contents of the intermediate products in the gas phase and fluid phase in the airtight one-stage completely autotrophic nitrogen removal system were determined by modern matter analysis measurement method, the nitrogen balance and the NH4+ removal ways of the system were studied. Results showed that 62% of NH4+ was converted to NO2-, NO3-, NH2OH, N2H4, NO, NO2, N2O and N2 under the microbial performance, N2 accounted for 90.07%, which was the main form of NH4+ removal.According to several mechanism hypothesis and denitrification reaction of one-stage autotrophic nitrogen removal process, different artificial nitrogen wastewaters were prepared, types and contents variations of compounds under different water conditions were monitored, and NH4+ removal pathways in one-stage autotrophic denitrification system were studied.Results showed that 6.72% of ammonia nitrogen was removed in the physical-chemical way, no more than 6.02% of ammonia nitrogen was converted by the conventional nitrification denitrification process, and about 87.26% of ammonia nitrogen was removed by the completely autotrophic nitrogen removal in one reactor process. But the effluent ammonium in the anoxic reactor, where enough NO2 were present, was equal to the blank system, and no ammonium was converted to such nitrogen compounds as NO2- and N2 by Nitrosomonas eutropha using NO2 as electron acceptor, which maybe caused by lack of the function bacteria. There were two ANAMMOX reaction pathways in the one-stage autotrophic nitrogen removal system. One way was that after part of NH4+ was oxidized to NH2OH under aerobic conditions, NH2OH and NO2- were converted to N2O under anaerobic conditions, at last N2O was further converted to N2 which realized the nitrogen removal; Another way was that at first NO2- was reduced to NH2OH, NH2OH reacted with NH4+ to form N2H4, which was further converted to N2 subsequently, realizing the nitrogen removal.
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