With the development of industry, the composition of sewage is becoming more and more complex. Some refractory organic substances and toxic substances need to be treated by microbial technology. Sewage has the conditions for the growth and reproduction of microorganisms which can get nutrients from the sewage to degrade and utilize the harmful substances and purify the sewage. Biological treatment of wastewater is a treatment method that uses the life activities of microorganisms to degrade organic pollutants in the wastewater in dissolved or colloidal state to purify the wastewater. The biological wastewater treatment technology is favored by people for its obvious advantages, such as low consumption, high efficiency, low cost, convenient and reliable operation and management, and no secondary pollution etc.