The invention discloses a graded purification treatment technology for mixed 
wastewater and belongs to the field of 
wastewater purification technologies. The graded purification treatment technology for the mixed 
wastewater comprises the following steps: step 1, carrying out primary filtering through a grid; step 2, treating through a grit catcher; step 3, treating through a primary sedimentationtank; step 4, carrying out biological treatment; step 5, carrying out secondary 
sedimentation; step 6, carrying out coagulation 
sedimentation; and step 7, filtering and disinfecting. A biological 
treatment procedure in step 4 is used for treating 
sewage through a biological contact oxidization method, and a 
biological membrane-forming bracket used in the biological contact oxidization method is aspecial membrane-forming bracket; the special membrane-forming bracket is provided with a micro-pore, an outer round 
pipe, an inner round 
pipe, a second connection 
pipe, a first connection pipe, a secondary connection pipe, a main connection pipe and a second ventilation hole, so that microorganisms including 
aerobic bacteria and the like in the water keep breathable; and sufficient 
oxygen gas inthe water is kept, the activity of the 
aerobic bacteria is promoted and the membrane-forming quality is enhanced, so that the 
sewage purification degree is improved.