| Two biological aerated filters with two different operating modes were used to treat domestic wastewater in this experiment. One was traditional biological aerated filters(1# reaction column) ,the other was pre-denitrification BAF( 2# reaction column). The two reaction columns were operated with up-flow modes with the process object of domestic wastewater ,and their filers all were ceramsite. A contrastive study was made on the start-up and biobiofilm formation and major factors which influenced organic matter removal and the denitrification performance of the two BAFs. The factors included media height, air to liquid ratio, hydraulic retention time, reflux ratio and so on. The main conclusions were drawed as below:1.The time needed for the start-up and biofilm formation of the two BAFs were al- most, for two BAFs 20 days were needed.2.The removal of CODcr did not keep in pace with that of NH4+-N in the process of biobiofilm formation. Under the condition of testing inflow of CODcr and NH4+-N, the BAF are two ways to run almost the same as removing CODcr law, pre-denitrification BAF of NH4+-N removal rate is less than BAF in the early of biofilm formation. Pegged to the success of the biofilm starts, two of the BAF operation CODcr, NH4+-N removal rate were to average at 70% and 90%.3.The result of optical bio-microscope observation showed that their aerobic biofilm section of the memory in the same biological phase, pre-denitrification of BAF in the memory hypoxia paragraph denitrification biological floc.4.When temperature was 28.0～40.24℃, this test compared reaction of the two columns at a high degree of filler along the way on the impact of the effectiveness of treatment under the different HRT(HRT=12h,10h,8h), when CODcr concentration in influent was 290.63～305.47mg/L, NH4+-N concentration was 37.21～40.24mg/L, the gas to liquid ratio was 3:1 and reflux ratio1:1. Experiments showed that the 1# reaction column had the best CODcr removal and its remarkable CODcr removal was achieved in the media height of 75～100cm,and 2# reaction column was 25～100cm. TN removal was mainly achieved in the media height of 25cm in 2# reaction column which removal efficiency was more than 70%. The NH4+-N removal efficiency of two columns were similar after media height of 50cm . The optimum media height for the removal of removal efficiency was more than 90%. The TN removal of 1# reaction column were not good its removal efficiency only about 23%. The TN removal of 2# reaction column mianly occurred in hypoxic zone and aerobic zone also had definite TN removal amount to about 60%.5.When temperature was 20.0～30.5℃, this test compared reaction of the two columns in the different (HRT=12h,10h,8h) on the impact of the effectiveness of treatment , when CODcr concentration in influent was 274.50～329.25mg/L, NH4+-N concentration was 34.83～41.86 mg/L, and reflux ratio of 2#reaction column was 1:1. Reaction of the two columns under the conditions of different HRT operated 5d respectively.The results showed that, the optimum effectiveness of treatment when HRT was 10h. The removal efficiency of CODcr,NH4+-N,TN in 1# reaction column were 72.63%,97.83%,21.36% respectively and 2# reaction column were 71.67%,99.45%,61.39% respectively.6.When temperature was 26.5～30.5℃, this test compared reaction of the two columns in the same HRT(HRT=10h) on the impact of the effectiveness of treatment , when CODcr concentration in influent was 274.50～327.23mg/L,NH4+-N concentration was 32.61～41.86 mg/L, and reflux ratio of 2# reaction column was 1:1. Reaction of the two columns under the conditions of different the gas to liquid ratio(3:1,4:1,5:1) operated 5d respectively.The results showed that, the optimum effectiveness of treatment when gas to liquid ratio was3:1.The removal efficiency of CODcr,NH4+-N,TN in 1# reaction column were 69.30%,88.31%,25.76% respectively and 2 # reaction column were 69.11%,98.28%,64.04% respectively.7.When temperature was 25.2～29.8℃, this test compared 2# reaction column in the different reflux ratio(100%,200% ,300%,400%) on the impact of the effectiveness of treatment ,when HRT was10h and gas to liquid ratio was 3:1, CODcr concentration in influent was 295.45～349.54mg/L,NH4+-N concentration was 32.61～44.18mg/L , reaction column under the conditions of different reflux ratio operated 5d respectively.The results showed that, the optimum effectiveness of treatment when reflux ratio was 3:1. The removal efficiency of CODcr,NH4+-N,TN in 2# reaction column were 72.66%,98.10%,80.29% respectively.8.In this test, the TN removal effectiveness of traditional biological aerated filters is not ideal ,only about 25% .And pre-denitrification BAF had better TN removal effectiveness ,amount to 80%.Two technics had ideal removal effects of CODcr, NH4+-N,but the removal mechanism and discipline were different. Because of the reflux, the pre-denitrification process had strong shock resistance ability,the effluent quality was relatively good,but it would increase the power consumption and operation costs.Therefore,if no need for TN removal especially when the CODcr concentration of wastewater is low,the traditional biological aerated filters were suggested.When the TN removal is needed,we should use pre-denitrification BAF. In addition,when the CODcr concentration of wastewater is high,and also had no need for TN removal,pre-denitrification BAF is suggested too.Because of the fast removal of CODcr in hypoxic zone,reducing the loading of aerobic zone,it also can realize TN removal. As to the reflux, the stability of the removal of CODcr and NH4+-N with pre-denitrification BAF was higher than traditional biological aerated filters.
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