Patent ID: 7166220

Claim:
A system for treating organic wastewater, said system comprising: a multistage treatment tank having at least two stages in series, each stage comprising a denitrification tank and a nitrification tank connected in this order; a pipe for distributing feed water to the denitrification tank in each stage; a means for filtering and separating at least a part of an activated sludge mixed liquor in at least one nitrification tank, wherein the filtration and separation means is a dynamic filter comprising a water-permeable filtration layer support material for forming a dynamic filtration layer thereon, and wherein the filtration and separation means is placed in the nitrification tank; a pipe for supplying at least a part of the concentrated sludge mixed liquor obtained by the filtration and separation treatment to the denitrification tank in the same stage; a pipe for taking out of a filtered water obtained by the filtration and separation treatment from the filtration and separation means; a sedimentation tank to be used for solid-liquid separation of at least a part of the activated sludge mixed liquor introduced from the nitrification tank in the final stage of the multi stage treatment tank; and a pipe for returning the deposited sludge collected from the sedimentation tank to the denitrification tank in the first stage.