Method for treating waste water from a catalytic cracking unit

Abstract

A method for treating waste water from a catalytic petroleum cracking unit is disclosed. The method includes receiving step, aeration step, settling step, and a discharging step. In the receiving step waste water from which hydrogen sulfide and ammonium have been stripped out is introduced into a biological treatment tank. In the aeration step, the waste water in the tank is subjected to aeration for a predetermined period of time. In the settling step, activated sludge within the biological treatment tank is settled for a predetermined period of time. And in the discharging step, the supernatant is discharged from the tank subsequent to the settling step. The total duration of the aeration step performed daily is set to no longer than 12 hours and the aeration step is performed intermittently. If these conditions are met, yeasts which form pseudohyphae will grow actively enough to facilitate settling and separation of activated sludge. In addition, treatment of an undiluted waste water, which has been impossible with the conventional process of continuous activated sludge treatment, cna be realized by the method of the present invention and not only does this allow the waste water to be treated consistently without deteriorating the quality of effluent but also the amount of excess sludge occurring is sufficiently reduced to lower the load of sludge treatment.