Study On An Integrated Nitrification And Denitrification Biofilm Reactor With Liquid Circulation Driven By Aertion

Based on traditional biological nitrogen removal theory, nitrogen removal involves nitrification of ammonia to nitrate or nitrite followed by denitrification of nitrate or nitrite to nitrogen gas. Nitrification is an aerobic process and carried out by the autotrophic microorganisms, whereas denitrification is restricted to anoxic conditions and realized by the heterotrophic microorganisms. For conventional nitrogen removal processes, nitrification and denitrification are carried out in separated tanks with different dissolved oxygen concentration or in a single reactor where aerobic and anoxic conditions are formed sequentially. Such processes usually need the recirculation of nitrified wastewater or the addition of external organic carbon and alkalinity. The investment and operation cost is high, and the land occupied is large. As to these problems, a novel integrated nitrification and denitrification biofilm reactor with liquid circulation driven by aeration is developed and applied as a single treatment unit for carbon and nitrogen removal of domestic wastewater. Nitrification and denitrification are accomplished respectively in the aerobic zone and anoxic zone of the reactor and the energy needed to ensure a good aeration is utilized for the circulation of nitrified wastewater.Simulated and practical domestic wastewater was used to investigate the carbon and nitrogen removal capacity of the reactor under various operation conditions and the operating parameters were optimized. Two years continuous experiment demonstrated that nitrification and denitrification were accomplished simultaneously in the single reactor and good balance between the two reaction processes could be obtained by adjusting the operating parameters as aeration rate, inlet position and baffle height et al. Nitrification had always been the rate-limiting reaction step of the nitrogen removal process when the influent organic carbon and nitrogen loading was enhanced. Under the condition of certain aeration rate, the increased organic carbon loading could strengthen the competition between the aerobic heterotrophs and authotrophic nitrifiers for oxygen and other nutrients and decrease the nitrification efficiency. Increasing the aeration rate and decreasing the baffle height could improve the DO concentration in the aerobic zone and buffering zone and decrease the impact of organic carbon oxidization on nitrification. When the DO concentration in the aerobic zone and buffering zone was kept at above 2.9mg/L and that in the anoxic zone below 1.5mg/L, COD and TN removal efficiencies of the reactor came up to 93% and 80% respectively with the influent organic loading 0.27~0.53kgCOD/(m~3. d) and nitrogen loading 0.1kgTN/(m~3. d). Removal capacity of the reactor is comparative to the A/O nitrogen removal process.Because nitrification and denitrification were achieved in a single reactor, the influent organic carbon components could be effectively utilized as electron donor for denitrification. Under the...