Method of removing phosphorus from wastewater

A method of biologically treating wastewater and producing a treated effluent, and after biologically treating the wastewater, removing phosphorous from the treated effluent, the method comprising:

• biologically treating wastewater and producing the treated effluent;
• and
• removing phosphorous from the treated effluent by:
• i. directing the treated effluent to a mixing tank;
• ii. mixing an iron or aluminum salt with the treated effluent in the mixing tank;
• iii. co-precipitating from the treated effluent iron or aluminum hydroxyphosphate and iron or aluminum phosphorous adsorption species having phosphorous adsorption sites;
• iv. mixing a flocculent with the treated effluent;
• v. mixing insoluble granular material with the treated effluent that results in the formation of ballasted flocs;
• vi. directing the treated effluent and the ballasted flocs to a settling tank and separating clarified effluent from sludge which includes the insoluble granular material and the iron or aluminum phosphorous adsorption species;
• vii. after separating the clarified effluent from the sludge, directing the sludge to a separator, and separating the insoluble granular material from the sludge to yield separated sludge;
• viii. concentrating the iron or aluminum phosphorous adsorption species in the wastewater by recycling a substantial portion of the separated sludge and mixing the separated sludge with the treated effluent causing the treated effluent to be concentrated with the iron or aluminum phosphorous adsorption species;
• ix. wasting a portion of the separated sludge;
• x. monitoring a phosphorus concentration in the clarified effluent;
• and
• xi. adjusting a sludge recycle rate to concentrate the iron or aluminum phosphorous adsorption species in the treated effluent such that the phosphorous concentration in the clarified effluent is 0.05 mg/L or less.