Waste water treating process

In a waste water treatment process employing activated sludge or biofilters in aerobic conditions, and then, anaerobic conditions to treat waste water containing phosphate ions, the improvement which comprises:

• a. adding activated sludge and sulfate reducing bacteria to the waste water, and immersing an iron contactor in waste water containing phosphate ions flowing into a waste water treatment tank;
• b. causing an agitating stream of the waste water to flow over the surface of the iron contactor or contactors at a velocity of 10 to 20 cm/sec.;
• c. under aerobic conditions, providing a dissolved oxygen concentration of 1 to 3.2 mg/l and a redox potential within the range from 31 200 to -400 mV to effect corrosion on the surface of said iron contactor, and cause iron ions to elute from said iron contactor;
• d. then under anaerobic conditions, holding the dissolved oxygen concentration at 0 mg/l in the treatment tank, the sulfate reducing bacteria acting on the surface of the iron contactor to cause corrosion on the surface of the iron contactor, and eluting iron ions from the iron contactor;
• and
• e. said iron ions eluted from the surface of the iron contactor under said aerobic and said anaerobic conditions, reacting with phosphoric acid ions in the waste water to produce insoluble compounds formed of iron and phosphate ions, and removing said compounds of iron and phosphate ions from the waste water.