It is the process of removing organic based solid substances in wastewater from wastewater by disintegration by microorganisms. At the end of the shredding process, the cleaned wastewater remains on top while the microorganisms settle on the bottom. This system is also called activated sludge system. The most common aerobic biological treatment application is the activated sludge process. Activated sludge processes consist of pre-precipitation pools, aeration pools, final precipitation pools and a disinfection unit. Disinfection is the process of removing bacteria and viruses in the wastewater treatment plant before the effluent is discharged.