In which part of the sewage treatment process - the decomposer bacteria present in the waste, is recycled into the beginning of the process :
Activated sludge treatment
Activated sludge treatment involves wastewater aeration in the presence of a microbial suspension, solid-liquid separation following aeration, discharge of clarified effluent, wasting of excess biomass, and the return of remaining biomass to the aeration tank. The settled biomass, called Return Activated Sludge (RAS), is then returned to the beginning of the aeration process where it will absorb fresh sewage to start the process again. This enables the processor to operate as a continuous cycle.
Primary treatment consists of temporarily holding the sewage in a quiescent basin where heavy solids can settle to the bottom while oil, grease and lighter solids float to the surface. The settled and floating materials are removed and the remaining liquid may be discharged or subjected to secondary treatment.
Tertiary treatment is the final cleaning process that improves wastewater quality before it is reused, recycled or discharged to the environment. The treatment removes remaining inorganic compounds, and substances, such as the nitrogen and phosphorus.