Study On Controlling Strategy And Mechanism Of Autotrophic Nitrogen Removal In One Reactor

As a cost-effective and energy-saving biological nitrogen elimination process, autotrophic nitrogen removal in one reactor has become a worldwide focus in this field. This study was carried out after successful start-up of reactors with the process of autotrophic nitrogen removal in one reactor. This thesis mainly contains three parts of research. First, the law of ORP and DO changes in one operation cycle was investigated on a reactor with continuous aeration. Second, the controlling strategy speeding the recovering process of the system was discussed based on the experimental data. Third, the ammonium removal mechanism of autotrophic nitrogen removal in one reactor process was examined and discussed. Conclusions were drawn as follows:After the damage of biofilm and activated sludge flocs in a system, serious nitrite accumulation occurred and nitrite concentration in the effluent of the system rose a lot. The instant DO adjustment had no distinct improvement for the system's nitrogen removal efficiency. In this condition, a two-step strategy, improving the reactor's performance after prompt bilofilm formation with high DO concentration, was suggested. It was also showed that the DO concentration should be adjusted timely according to the changes of biofilm thickness and flocs diameter. The total nitrogen removal rate reached about 80% under this strategy.In one operation cycle of the continuously-aerated system, the ORP curve rose with a high speed at the beginning and the curve's slope fell dramatically nearly at the time ammonium transformation was completed, while the DO curve rose sharply after the time. Therefore, ORP and DO could both be used as process-control parameters. The combination of ORP and DO was suggested for the control of aeration.The results of mechanism batch tests showed that: there was no Nitrosomonas denitrification in the system; there was probably Anammox reaction with two different pathways, which still needed further proof from gas analysis; there was nitrogen removal from traditional denitrification but the amount of removed nitrogen was very limited. The max autotrophic nitrogen removal activity were 0.0034gN·g^-1VSS^-1d^-1,0.0087gN·g^-1VSS^-1d^-1,0.016gN·g^-1VSS^-1d^-1 for activiated sludge, biofilm on the carrier and biofilm on the reactor walls respectively. The max nitrition activity were 0.015 gN·g^-1VSS^-1d^-1,0.026 gN·g^-1VSS^-1d^-1,0.035 gN·g^-1VSS^-1d^-1 for activiated sludge, biofilm on the carrier and biofilm on the reactor walls respectively. And the max Anammox activity were 0.011 gN·g^-1VSS^-1d^-1,0.021 gN·g^-1VSS^-1d^-1, 0.027 gN·g^-1 VSS^-1d^-1 for activiated sludge, biofilm on the carrier and biofilm on the reactor walls respectively. These three kinds of activities of biofilm were all higher than that of activiated sludge. .