Research On Biological Nitrogen Removal With Nitrification And Denitrification Via Nitrite Pathway In MBBR Reactor

Water pollution is the major reason for the shortage of water resources in China. Among the various kinds of contaminants causing water pollution, pollution of nitrogen is more and more serious, and has become the focal point of researches in the future on waste water treatment. The process of nitrification and denitrification via nitrite, which is a newly-developed technology for denitrification in recent years, produces little sludge, runs effectively and compactly, saves energy, and has been applied more and more widely. There are many middle and small cities in our country, but the quantity of sewage is little, as a result, it’s not suitable to construct large wastewater treatment plants intensively. As a new wastewater treatment process, MBBR has the advantages of both activated sludge method and biomembrance process, and it’s appropriate for small towns because of its simple operation and saving in money and space.The paper proposes the method of nitrification and denitrification via nitrite in MBBR, and explores the approaches to achieve it. In the meanwhile, it makes studies about the effect of factors (such as HRT, PH, NH3-N load, organic load and concentration of DO), on the nitrification and denitrification via nitrite in MBBR, along with researches of relevant dynamics.Achievement of the nitrification and denitrification via nitrite in MBBR: making the MBBR runs in high DO concentration (2.0mg·L-1) and low DO concentra-tion (0.5～1.0mg·L-1) alternately and continuous. Through25-days cultivation, the accumulation rate of NO2--N reaches75.94%, and the nitrification and denitrifica-tion via nitrite is realized.The experiment of influence factors:DO concentration has the most significant impact on the nitrification and denitrification via nitrite in MBBR. When the concen-tration of the DO is bigger than0.81mg·L-1, the NO2--N concentration in the effluent decreases by a large margin; when the concentration is above1.14mg·L-1, the NO2--N concentration in the effluent increases gradually, and the accumulation rate of NO2--N drops to50%or lower, which means MBBR has transferred to traditional full nitration denitrifying denitrification.HRT has only little influence on the nitrification and denitrification via nitrite in MBBR. When HRT is longer than12h, the removal rate of NH3-N is higher than70%, and the NH3-N concentration in effluent is lower than10mg·L-1, with the accumulation rate of NO2--N above70%. pH in the system influences the nitrification and denitrification via nitrite greatly. When pH lies between8and9, the removal rate of NH3-N is77.4%, the average concentration of NH3-N in effluent is8.35mg·L-1, the accumulation rate of NO2--N is71.89%. NH3-N load and organic load also plays a big role to affect the result of the experiment. In the condition of high organic load and low NH3-N load, the accumulation rate of NO2--N is reduced, which demonstrates that the nitrification and denitrification via nitrite fits the sewage in low C/N.Finally, based on the Monod substrate biodegradation model, the paper establi-shes the dynamics equations of NH3-N’s utilization rate, and the equations of AOB’s growth kinetics. Besides, the dynamics parameters are got by using a differential method.