The process of microbial sludge with metabolic activity growing on the filler in biological treatment system is called biofilm formation, and it is also the process of cultivation and domestication of membranous sludge in biofilm treatment system. Therefore, the biofilm process has just been put into operation. On the one hand, microorganisms grow and multiply until the surface of the filler is covered with biofilm, and the number of microorganisms meets the requirements of sewage treatment.