A bioreactor for treating sewage comprising: an aerobic tank including a mixing cell for receiving sewage and mixing the sewage with activated sludge; an aerobic reactor tank for allowing the activated sludge to adsorb organic substance existing in the sewage therein; a backwashing cartridge filter for removing floc resulting from growth of the activated sludge adsorbing the organic substance; and an anaerobic tank for carrying out a denitrification process, using anaerobic ammonium oxidation bacteria, for denitrifying treated water flowed through the backwashing cartridge filter; wherein the backwashing cartridge filter comprises: a cartridge filter housing; a cartridge filter member fixedly installed inside the cartridge filter housing for separating the floe and the treated water, wherein the cartridge filter member includes pores for separating the floe and the treated water using a difference in size between the floc contained in the sewage discharged from the aerobic reactor tank and the pores such that the separated floc remains outside the cartridge filter member while the treated water flows through the cartridge filter member towards the anaerobic tank; a transfer port arranged at an upper or lower end of the cartridge filter member for discharging the treated water flowed through the cartridge filter member; and an inlet for introducing washing water into the backwashing cartridge filter such that the washing water injected through the inlet is forced to pass through the cartridge filter member from an inside of the cartridge filter member to the outside of the cartridge filter member for removing the floe adsorbed to the cartridge filter member into the cartridge filter housing. an aerobic tank including a mixing cell for receiving sewage and mixing the sewage with activated sludge; an aerobic reactor tank for allowing the activated sludge to adsorb organic substance existing in the sewage therein; a backwashing cartridge filter for removing floc resulting from growth of the activated sludge adsorbing the organic substance; and an anaerobic tank for carrying out a denitrification process, using anaerobic ammonium oxidation bacteria, for denitrifying treated water flowed through the backwashing cartridge filter; wherein the backwashing cartridge filter comprises: a cartridge filter housing; a cartridge filter member fixedly installed inside the cartridge filter housing for separating the floe and the treated water, wherein the cartridge filter member includes pores for separating the floe and the treated water using a difference in size between the floc contained in the sewage discharged from the aerobic reactor tank and the pores such that the separated floc remains outside the cartridge filter member while the treated water flows through the cartridge filter member towards the anaerobic tank; a transfer port arranged at an upper or lower end of the cartridge filter member for discharging the treated water flowed through the cartridge filter member; and an inlet for introducing washing water into the backwashing cartridge filter such that the washing water injected through the inlet is forced to pass through the cartridge filter member from an inside of the cartridge filter member to the outside of the cartridge filter member for removing the floe adsorbed to the cartridge filter member into the cartridge filter housing. a cartridge filter housing; a cartridge filter member fixedly installed inside the cartridge filter housing for separating the floe and the treated water, wherein the cartridge filter member includes pores for separating the floe and the treated water using a difference in size between the floc contained in the sewage discharged from the aerobic reactor tank and the pores such that the separated floc remains outside the cartridge filter member while the treated water flows through the cartridge filter member towards the anaerobic tank; a transfer port arranged at an upper or lower end of the cartridge filter member for discharging the treated water flowed through the cartridge filter member; and an inlet for introducing washing water into the backwashing cartridge filter such that the washing water injected through the inlet is forced to pass through the cartridge filter member from an inside of the cartridge filter member to the outside of the cartridge filter member for removing the floe adsorbed to the cartridge filter member into the cartridge filter housing.