If we want to explain it in the simple way, we can say PGA biofilter contains a main tank that is full of a bed containing microorganisms. this bed has a porous texture and the capacity of fixing more than 1 billion microorganisms per 0.5 cm^3. The stabilization process has been completely assured without the possibility of releasing or reducing amount of the microorganisms. Based on the type of pollutant present in the sewage, one or more specific microorganisms will be used in the system. Also, the volume of biofilter used in the system depends on the volume of water or wastewater that needs to be purified. It should be mentioned that in PGA biofiltraion system the physical and chemical pre-treatments also have been used such as pH adjustment and ozonation if needed.