APPARATUS FOR TREATING ORGANIC SEWAGE

摘要

PURPOSE:To reduce operation cost and installation cost by providing a biological treatment tank in succession to a biological nitrification/denitrification tank and further providing a recirculation tank in which an activated sludge slurry is allowed to flow. CONSTITUTION:The activated sludge slurry 9 flowing out of a biological treatment tank 18 is guided to a recirculation tank 10, and an inorg. flocculant 11 and an alkali agent 12 are added to said tank 10 to perform flocculation treatment in an acidic region. The flocculated slurry 13 is supplied to the module of an ultrafiltration membrane separator 14 at high flow velocity by a pump to be separated into a UF membrane transmitted water 15 and a flocculated conc. slurry 16. The greater part of the flocculated conc. slurry 16 is recirculated to the recirculation tank 10 and a part 17 thereof is returned to a biological nitrification/ denitrification tank 2 in order to hold the concn. of the activated sludge in said tank 2 to a predetermined value. By this method, the lowering of nitrification/denitrification reaction is prevented without bringing about a lowering of pH.