Biofilm process is an aerobic biological treatment technology of wastewater in parallel with activated sludge process. It is a fixed membrane method, which is artificially strengthened in the process of self-purification of sewage soil, mainly to remove soluble and colloidal organic pollutants in wastewater. Simply put, sewage flows on the surface of the filler, and after a certain period of time, microorganisms will attach to the surface of the filler to grow and reproduce, forming a thin biofilm, thus promoting the purification of water.

Biofilm method has an important carrier-filler. Does it look like lotus root in cold noodles? Nutrients and inoculated microorganisms in sewage attach to the surface of these "surface lotus root" fillers, and adsorb and remove pollutants in water to achieve the purpose of purifying water quality, similar to the purification effect of aquatic plants in rivers and lakes.

Compared with other sewage treatment technologies, biofilm process has strong adaptability to the change of sewage quality and quantity, produces less excess sludge, and can also treat high-concentration sewage. Of course, there are some shortcomings. The first is the investment cost. In fact, the microorganisms attached to the filler are difficult to control and the operation flexibility is poor. Especially in urban sewage treatment, its efficiency is slightly lower than that of activated sludge method.