Mathematical Simulation Of Nitrogen Removal Via A Partial Nitrification-Anaerobic Ammonium Oxidation In A Membrane-aerated Biofilm Reactor

Anaerobic ammonia oxidation(Anammox) illustrate a good prospect of application in the nitrogen removal in the 21st century,for it has serval advantages such as no organic carbon needed,less oxygen demanded and sludge produced.If we want to achieve Anammox,half of the ammonia should be oxidizing to nitrite first, then the Anammox process can be occurred with the nitrite and the ammonia remained.But some controllable factors to achieve Anammox still did not make clearly resloved till now,such as dissolved oxygen control,high-efficiency microorganisms retain and the cooperation of two ammonia oxidizing bacterials. Membrane-aerated biofilm reactor realized the counter-diffusion of oxygen and substrate,improved the diffuser efficiency of the oxygen and substrate,the flux of oxygen from the gas to the biofilm matrix can be easily controled in addition.This paper look back the development history of the actived sludge model of the International Water Association(IWA),developing a mathmatic model of partial nitrification-anaerobic ammonia oxidation coupled process based on the Actived Sludge Model 1(ASM1),choosing parameters,implement a simulation and checking by the selecting experiment data.Then carried out the simulation and analyzing of the stratification and the total nitrogen removal efficiency in a membrane-aerated biofim reactor.The simulation results show that the mathmatic model can simulate the nitrogen removal via a partial nitification-anaerobic ammonia oxidation coupled process in a membrane-aerated biofilm reactor quite well,prove our model is correct and effective.The rusults show that formed markedness stratification structure in the biofilm.The aerobic ammonia oxidizers were growing near the menbrane,the anaerobic ammonia oxidizers were growing near the bulk liquid.The aerobic ammonia oxidizers and nitrite oxidizers can coexist in the aerobic zone,and the nitrite oxidizers will die out along with the biofilm become thicker.The simulation results show that flux ratio of oxygen and ammonia(J_O2/J_NH4)has salience effect to the stratification in the biofilm.When the J_O2/J_NH4 less than 0.25,there is no stratification appear,along with J_O2/J_NH4 increment,the time to appear markedness stratification structure cut down quickly;when the J_O2/J_NH4 equal to 1.5,the time to appear markedness stratification structure is 154d,this is the shortest time in our simulation results.Along with the J_O2/J_NH4exceed 1.5,the time to appear markedness stratification structure become successive steps increasing.This is because the oxygen is excessive.Larger J_O2/J_NH4 will lead to thicker aerobic zone,but can not form appropriate anaerobic zone.The simulation results show that, J_O2/J₍NH₄ equal to 1.5 is the best start-up condition of the membrane-aerated biofilm reactor,less than the theoretical point.When the J_O2/J_NH4 keep constant,along with the biofilm growth,the total nitrogen removal efficiency will increased,but when the biofilm thickness exceed certain value(about 2000 micrometer),the total nitrogen removal efficiency will decreased immediately,this is probably because the difficult of diffuion in thicker biofilm.The optimization biofilm thickness is between 1500 and 2000 micrometers.