Enhanced Biological Phosphorus And Nitrogen Removal With Five-Tank Integrated Activated Sludge System

Five-tank integrated activated sludge system, a new wastewater treatment process with the function of phosphorus and nitrogen removal was developed on the basis of such process as UNITANK and triple oxidation ditch. This process is composed of five hydraulicly connected rectangle tanks. The alternation of anaerobic, anoxic, aerobic and settling state was realized by timely and spatial control change to these five tanks. Mixed liquid and sludge are recirculated automatically by location transition of inlet and outlet without additional sludge or mixed liquid recirculation. This process runs with constant water level and high phosphorus and nitrogen removal rate.Every tank in this process is a CSTR(completely stirred tank reactor). All the five tanks constitute a group of CSTR cascade. On the whole, this process has the characteristic of puff flow reacter. So this process has high removal efficiency and can endure some shock load. Compared with UNITANK, the alternation of anaerobic, anoxic and aerobic state is more incident with timely and spatial change.Thereby, this process creates more suitable growth environment for polyphosphate accumulating organisms(PAOs) and enhances phosphorus and nitrogen removal.These five rectangular tanks have wall and motherboard in common with close collocation and stable structure. The construction investment and location space are spared. There are two side tanks for alternating outlet. Additional settling tank, sludge and mixed liquor recirculation equipment are omitted. This process runs at constant water level with small water head loss. Power consumption is greatly saved because of low power load. This system is automatically operated under the control of PLC (Programmable Logic Controller). Running mode and controlling state can be adjusted conveniently.A pilot scale test was applied in Nanjing Jiangning Development Zone Wastewater Treatment Plant. The preferable parameters of this system and its adaptability to different wastewater quality were studied. The process and mechanism of phosphorus and nitrogen removal were explored by tracking test. The relation of the characteristic points of ORP and pH with denitrification, phosphorus release and nitrification under continuous flow operation was analyzed. The feasilility to use these characteristic points as feedback for phosphorus and nitrogen removal was also discussed. The phenomenon of denitrifying phosphorus removal in this system was studied. The denitrifying phosphorus removal ability and polyphosphate accumulating organisms composition of the sludge in this reactor was detailedly investigated. The relativity of the biofacies to phosphorus and nitrogen removal in this reactor was also analyzed. The plug flow model of sludge in this system was founded to theoretically predict sludge distribution during operation, which was also contrasted to that in three-tank alternating activated sludge system such as UNITANK.Anaerobic, anoxic and aerobic state appeared alternately in one tank on different phases and on one phase in different tanks. Accordingly, phosphorus uptake, nitrification and denitrification arose. Diverse microorganism and electron acceptors were utilized for phosphorus and nitrogen removal resulting with...