| With the development of the study of sewage treatment, more and more new reactors are used. External loop three phase fluidized bed reactor as one of the potential reactors has been used recently. Owing to its strong microbial activity, the competence of nick burthen is very power, smaller space, lower energy consumption, very phases in the reactor are symmetrical,the effect of transfermentis good, it is concerned by more and more people. Treatment of landfill leachate has been concerned because of its complex composition, high concentration of pollutants and the difficulties to deal with.This paper outlined the research achievements about fluidized bed reactor at home and abroad, introduced the study progress, summarized the current research problems, and put forward a direction for the further research.At first, the experiment on biofilm formation in an external loop three phase fluidized bed reactor was presented in this paper. The effect of the value of sludge addition and C/N ratio were studied. The experiment result showed that at the temperature of 20-30℃, when the diameter of granular activated carbon was 0.125-0.5mm, the value of sludge addition at 2g·L-1 was more propitious to the formation of biofilm than 5g·L-1. Formation of biofilm in fluidized bed was the rapidest when C/N ratio was between 8and12. It was difficult and leaned to form filamentous bulking sludge when C/N≥14. On the basis of the success of attached film, the influence of hydraulic residence time (HRT) on the value of suspended sludge and the value of biofilm was studied. The result showed that while HRT expended and the value of suspended sludge increased, the value of biofilm also increased, when HRT was between 1-3h. But when HRT exceeded 5h, HRT expended and the value of biofilm decreased. When HRT was between 4-5h, the value of suspended sludge and the value of biofilm were steady.The optimum condition of external loop three phase fluidized bed reactor with synthetic wastewater were investigated and the factors which affect the biological nitrogen removal process under the condition were also studied. Results showed that the main factors included C/N ratios, pH values and aeration flow rates. When the C/N ratio was 7, there were much water in effluent because of the lack of carbon source, the simultaneous nitrification and denitrification (SND) couldn't carry out fully. When it was 19, the concentration of ammonia in effluent was very low, but COD with a higher level. When the C/N ratio was 12, the concentration of ammonia was also low and COD had a significant drop. So the appropriate C/N ratio was 12. PH is a very important factor in the membrane reactor, impacting the efficiency and the operation of the membrane reactor, because pH directly affects the growth of the membrane microbiology. The study found that the most appropriate pH was from 7.5 to 8.0, while at this time SND had the best effect. When pH was lower than 7.5, the concentration of NO2--N and NO3--N in effluent were high. When pH was higher than 8.0, the effect of SND is far behind the former. When pH was higher than 9.5, the biofilm started to fall from the carriers. There is a positive correlation between taeration flow rates and DO, as the fluid power of the carriers is provided by aeration, aeration flow rates affect the fluid power and DO at the same time. If the aeration flow rate is too low, the power wasn't enough so that the carriers couldn't be fluided fully. The lack of DO would limit nitration. While when aeration rate is too high, the biofilm will be washed off, and that also impact the denitrification effect. The aeration rate 0.06m3s-1 treatment seemed to be the best one.At last, we used the system composed with the external loop three phase fluidized bed reactor and constructed wetland treated the landfill leachate. We studied the changed of the water quality behind the lanfill leachate treated by this system. The experimental results indicated that the COD and NH4+-N of the influent reduced from 4000 mgL-1 and 300 mgL-1 to 1500 mgL-1 and 150 mgL-1 after the external loop three phase fluidized bed reactor and steady at 200 mgL-1 and 10 mgL-1behind treated by the constructed wetland.the heavy metal of Cd,Zn,Pb were also reduced for treatment by external loop three phase fluidized bed reactor. They were steady at 0.01 mgL-1,0.5 mgL-1,0.1 mgL-1 from0.12 mgL-1,3.0 mgL-1,1.4 mgL-1 because of the constructed wetland. We also compared the different plants for the efficiency, the results showed that whatever plants, there was small effect of the efficiency of the COD and NH4+-N, but the effect of heavy metal was markedness. All in all, in theory the ststem what used treated the landfill leachate is feasible.
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