Airlift Loop Bioreactor And The Design Of Automatic Control System For The Reacror

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 extemal organic carbon and alkalinity. The investment and operation cost is high, and the land occupied is large.In order to solve these problems, an airlift loop reactor is designed. The reactor is fixed growth biomembrane reactor and is divided into several zones and different bacteria grew dominantly in different zones. Wastewater, driven by aeration, flow through different zones of the reactor at different stages to be treated. As a results, organic pollutants and nitrogen are removed.Simulated and practical domestic wastewater is used to investigate the carbon and nitrogen removal capacity of the reactor under various aeration and hydraulic residence time conditions. Experimental results demonstrated that the reactor reaches the top effluent water quality and removal capacity when aeration rate is 900L/h and hydraulic residence time is 24 hour. Keep DO (dissolved oxygen) levels of the aerobic zone at 4.50～5.00mg/L by experiments. In this paper, the automatic control system contains Bang-Bang control, and chooses DO for the control parameter. The system uses a closed-cycle discrete feedback to monitor DO in the aerobic zone of the reactor. The sensor measures DO continuously, then transmits the signal of DO into controller for comparing the measured signal with control range, and finally the controller changes the state of the control valve. The experiment under continuous flow mode during 24 hours demonstrated that effluent COD and TN is below 20rag/L, COD removal efficiency is beyond 90%, and TN removal efficiency is beyond 80%. The experiment indicates that the control system can be in good operation, and it can control the working of the airlift loop reactor in effect.