WASTEWATER TREATING APPARATUS AND WASTEWATER TREATING METHOD

PROBLEM TO BE SOLVED: To provide a wastewater treating apparatus and a wastewater treating method by which production amount of excess sludge can be further reduced. SOLUTION: The wastewater treating apparatus 10 is provided with a first sedimentation basin 50 for carrying out solid-liquid separation of water to be treated, an activated sludge treatment tank 12 for carrying out activated sludge treatment of the water to be treated subjected to solid-liquid separation, a final sedimentation basin 24 for carrying out solid-liquid separation of treated matter containing sludge, a first sludge returning line L5 for returning a part of the treated matter containing sludge of the activated sludge treatment tank 12 to the activated sludge treatment tank 12, a preliminary thickener tank 56 for thickening further a part of the treated matter containing sludge of the activated sludge treatment tank 12, a sludge modification tank 34 for carrying out aeration of the thickened sludge and a second sludge returning line L7 for returning the sludge aerated by the sludge modification tank 34 to a runoff channel 54 of the first sedimentation basin 50. By this constitution, the sludge in the sludge modification tank 34 is made to a starvation state, amount of SS held in whole arrangement can be increased and production amount of excess sludge can be further reduced. COPYRIGHT: (C)2008,JPO&INPIT