A sewage treatment system includes dehydration means to dehydrate the received surplus sludge and/or the received return sludge; a microbial material production device configured to supply oxygen to the dehydrated sludge received from the dehydration means while maintaining the temperature of the dehydrated sludge to subject the dehydrated sludge to aerobic fermentation, thereby producing a microbial material; water feeding means configured to feed water from any part of the sewage treatment system to the after-mentioned microbe activation device; a microbe activation device configured to receive the microbial material from the microbial material production device, and supply the water from the water feeding means to the received microbial material; and oxygen supply means configured to supply oxygen to the sewage at any position of the relay pump station; wherein the sewage is sent from the relay pump station to the sewage treatment facility.