PURPOSE: To perform high degree treatment of treated water and effective utilization of phosphorus components in combination by removing and recovering the phosphate ions left in the treated water by activated sludge, and reusing these as nourishing sources for the activated sludge treatment.
CONSTITUTION: The mixed liquids subjected to a sludge treatment in an aeration tank 2 are shifted into a settling tank 3, and the treated liquid separated from activated sludge is supplied to a mixing tank 4. Here, a Ca ion-contg. neutral salt soln. 5 is added thereto, and the liquid is supplied to a packed tower 6 packed with fine granular MgO or Mg(OH)2. Thereby, the phosphate ions left in the treated liquid are removed by about ≥90%, and are discharged to the outside of the system. At a proper point of time, the operation is suspended temporarily, and a dilute aq. inorg. acid soln. is flowed down in the tower 6 from an acid storage tank 7, whereby the insoluble phosphates in the packed beds are dissolved away and are stored in a storage tank 8. The dissolved liquid is controlled to 6W8 pH, after which it is added to the waste water in a control tank 1 so as to be reused as nourishing sources for activated sludge.
ASANO TADAHIKO
OOKUMA MASATSUNE
KATAYAMA SAKAE
