Activated sludge method is a kind of aerobic biological treatment method of sewage, invented in 1912 by Clark and Gage of the United Kingdom. Nowadays, the activated sludge method and its derivative improved process are the most widely used methods for treating municipal wastewater.

The biofilm method is to make microorganisms adhere to the surface of the carrier. When the sewage flows through the surface of the carrier, it affects the pollutants through the adsorption of organic nutrients, the diffusion of oxygen into the biofilm, and the biological oxidation that occurs in the film. Progressive decomposition.