Abstract: A “fluidized bed reactor” (FBR) is a kind of reactor system that may be utilized to conduct a number of chemical processes with multiple phases. A fluid is pumped thru a solid concentrated material in the reactor (generally a catalyst probably formed as small spheres) at sufficiently high speeds to suspend substance and allow it to function as a fluid. The paper discusses aboutfluidized bed in waste water treatment.Application of fluidized bed reactor in treatment of waste such as municipal waste water in order to treat sewage, landfill leachate in order to remove COD, ammonia which affects environments and rendering waste along with proper analysis and results is also discussed. Importance of primary clarifiers and secondary clarifiers are presented in the paper.