NOVELTY - A wastewater treatment system comprises anaerobic region (2b), anoxia region (2c), aerobic region (2d), activated sludge which has 2nd concentration of 2600-5000 mg/L and contains Bacillus bacteria with 1st concentration of 108-1010 pieces/mL, reaction tank (2) which performs removal of nitrogen and phosphorus from wastewater and decomposition of raw sludge in wastewater, and sedimentation basin (3) where activated sludge contained in wastewater and discharged from reaction tank is precipitated and isolated.    USE - A wastewater treatment system (claimed).    ADVANTAGE - Service life of wastewater treatment system is prolonged, running and maintenance costs are reduced, the need to implement countermeasures against offensive odor of hydrogen sulfide generated during wastewater treatment is eliminated, and labor is improved.    DETAILED DESCRIPTION - A wastewater treatment system comprises anaerobic region (2b), anoxia region (2c), aerobic region (2d), activated sludge which has 2nd concentration of 2600-5000 mg/L and contains Bacillus bacteria with 1st concentration of 108-1010 pieces/mL, reaction tank (2) which performs removal of nitrogen and phosphorus from wastewater and decomposition of raw sludge in wastewater, sedimentation basin (3) where activated sludge contained in wastewater and discharged from reaction tank is precipitated and isolated, sludge return unit which returns return sludge (42) from activated sludge isolated in sedimentation basin to reaction tank in order to maintain activated sludge in reaction tank at 2nd concentration, spin-drying unit (7) which carries out dehydration by using residue of activated sludge isolated in sedimentation basin as surplus sludge (43), and mineral powder addition unit (8) which adds mineral powder with silicic acid to reaction tank based on concentration of wastewater supplied to reaction tank in order to maintain bacteria in activated sludge returned from sedimentation basin at 1st concentration. An INDEPENDENT CLAIM is included for wastewater treatment method.    DESCRIPTION OF DRAWING(S) - The drawings show a block diagram and sectional views of the wastewater treatment system. (Drawing includes non-English language text).    Reaction tank (2)    Anaerobic region (2b)    Anoxia region (2c)    Aerobic region (2d)    Sedimentation basin (3)    Spin-drying unit (7)    Mineral powder addition unit (8)    Return sludge (42)    Surplus sludge (43)