Disclosed herein is a particle separation apparatus. The particle separation apparatus includes: a bioreactor; a first flow path through which the sludge is discharged from the bioreactor; a first filter including a first mesh separating the granular microorganisms contained in the sludge according to size; a second flow path into which an effluent having passed through the first filter flows; a third flow path connected to the second flow path to discharge the effluent outside; a fourth flow path connected to one side of the second flow path and mounted on a surface of the first filter connected to a surface of the first filter with the second flow path mounted thereon; a fifth flow path through which the effluent having been discharged from the fourth flow path and passed through the first filter flows into the bioreactor; and a first pump creating a flow of the effluent.