| The Biological Aerated Filter (BAF) is a simple, high-efficient; low-consumptive for municipal sewage treatment corresponds to the situation of china developed rapidly in last ten years will be one of the important technical approaches to solve the water pollution and shortage problem faced china. However, there still some problems that need further study in BAF with respect to media function, aeration mode, treatment mechanisms, operational factors, backwashing and influent control, factors,backwashing and influent control. A bench scale experimental study was carried out with synthetic domestic wastewater as the model water, focusing on the start-up of reactor, treating efficiency and biofilm characteristic. The optimization operational parameters are determined by studying the environmental condition to influence the removal efficiency of pollutants; but also a depth studying was carried out by focusing on the treating efficiency and treatment mechanisms of the rice hull which was using in the BAF as filter material. It can be drawn the following conclusion derived from the experiment results.(1) It take about 9 days to succeed in cultivating biofilm using of the method of continuous flow following with soaking rice hull and intermission cultivating, when the removal rates of CODcr and NH3-N gets to 85% and 75% and the reactor run stable.(2) The experimental results showed that the removal rate of CODcr, NH3-N and TP in BAF system comes up to 88.4%, 63.9% and 45.7% respectively.(3) Under different conditions of three hydraulic loading, the backwash interval of BAF was 30h, 28h and 22h respectively. The backwash regimes of gas combined with water has a good backwash effect. The backwash intensity of gas and water was 6.5～7.5L/(m2·S) and 1～2L/(m2·S) respectively.(4) The microscopy results show that as microbe species in BAF distributed spatiotemporally, dominant bacteria for different height of filter material was distinctive. Along the fluent direction the superiority protozoa in biomembrane are the flagellates, the free swimming ciliate, and the sessile ciliate in turn, demonstrating the obvious plug flow characteristic.(5) Through testing the factors on BAF performance, it is found that the removal efficiency of CODcr changed little with enhancement of hydraulic loading, which whereas had the negative effect on removal efficiency of NH3-N and TP. When the ratio of air to water was 10:1, the removal efficiency of organic pollutants, NH3-N and TP could both be improved. The operating mode of aeration has evident influence to the removal rate in BAF system. The reactor could maintain better removal efficiency of CODcr, NH3-N and TP, if the operating mode keeping with aeration lasts 1 hour and anoxic lasts 1 hour. With the CODcr volume loading higher, the removal of NH3-N has a gradual lower. When NH3-N volume loading from 0.06 kg/ (m3·d) to 0.45kg / (m3·d), the nitration ability of reactor will be weakened gradually with the increase of NH3-N volume loading. To the BAF in which 75cm height filter bed is used the optimal region of CODcr removal is 0～45cm, the optimal region of NH3-N removal is 0～30cm, at 45cm height, the TP will be removed mostly.(6) According to the results of influencing factor experiment, the optimization operational parameters as follows: operation flow is 2.7 L/h, hydraulic loading is 0.28m3/m2·h, gas-water ratio is 20:1, the operating mode is aeration lasts 1 hour and anoxic lasts 1 hour, the CODcr volume loading is above 1.82 kg/(m3·d), the NH3-N volume loading is above 0.15 kg/(m3·d), the concentration of TP is above 1.7 mg/L. On these conditions, the reactor had a better removal effect to CODcr, NH3-N and TP.(7) The removal mechanisms of CODcr, NH3-N and TP were discussed. Through the results of feasibility analysis and proving experiment with rice hull BAF, we can conclude that the rice hull BAF was a feasible reactor on treating domestic wastewater.
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