Recovery of high purity phosphorus from municipal wastewater secondary effluent by a high-speed adsorbent

High purity phosphorus was recovered from municipal wastewater secondary effluent as phosphate, using a newly developed phosphorus adsorption and recovery system. A high-speed adsorbent having a unique porous structure was used in this system. The secondary effluent, showing total phosphorus (TP) of 0.1–2.1 mg P/L, was passed through an adsorbent packed column at high space velocity (SV) of 15 h⁻¹. The TP of the treated water was as low as 0.02–0.04 mg P/L, indicating that 97% of phosphorus in the secondary effluent was removed. The removed phosphorus was desorbed from the adsorbent by passing a sodium hydroxide aqueous solution through the column. Calcium hydroxide was added to this solution to precipitate the phosphorus as calcium phosphate. This precipitate was neutralized with hydrochloric acid aqueous solution, washed with water, and then solid–liquid separation was performed for the phosphorus recovery. The main constituent of the recovered phosphorus was apatite-type calcium phosphate, with 16% phosphorus content, which matched that of high-grade phosphorus ore. The hazardous elements content of the recovered phosphorus was exceedingly low. Therefore the recovered phosphorus can be applied to an alternative for phosphorus ore, or to a phosphate fertilizer.