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With the rapid development of our economy and the constantly improvement of people’s living standards,the nitrogen content of municipal sewage has increased in many cities,and the low C/N ratio phenomenon occurs.The "anoxic-aerobic-anoxic" alternating biological aerated filter process was proposed to utilize carbon source in domestic sewage more fully for denitrifycation, and the performance on contaminants was studied.The effect of factors such as gas-water ratio, hydraulic loading and change cycle of influent flow on system’s performance was also analysed. Orthogonal experiment was finished to ascertain the optimum technological parameters, and than the system’s performance on the low C/N ratio urban sewage was studied.The study results showed that:(1) The optimum technological parameters of alternating biological aerated filter process for sewage treatment is:2nd-stage filtration column’s gas-water ratio is7:1, the hydraulic loading is1.0m3/(m2h), the change cycle of influent flow is90min. Under this condition: when the raw water COD,SS,NH4+-N, TN, TP concentration were respectively187mg/L,88.4mg/L,49.7mg/L,57.7mg/L and5.92mg/L,COD/TN5.1, the effluent COD, SS, NH4+-N, TN, TP concentrations were respectively15.19mg/L,8.15mg/L,5.73mg/L,14.15mg/L and3.06mg/L, the removal rates respectively reached91.89%,90.78%,88.47%,75.48%,48.29%. Besides the TP concentration of effluent,all of the water quality index could meet the A standard "Discharge standard of pollutants for municipal wastewater treatmentplant (GB18918-2002)", but the TP removal rate increased about15%～25%compared to traditional BAF process.(2)The combined water and air backwash was finished respecttively on the3filtration columns, the system performed well after backwash, and the effluent quality could quickly returned to normal level.The backwash duration was10min, and the backwash water flow of1st and2nd filtration columns were15L/h,while the2nd filtration column’s was25L/h, and three filtration columns’ backwash gas-water ratio were all1:1,1st and2nd filtration columns’ backwash cycle was2d, while the2nd filtration column’s was3d.
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