Phosphorus Removal from Lake Water Using Basic Oxygen Furnace Slag: System Performance and Characterization of Reaction Products

Effectiveness of basic oxygen furnace slag (BOFS) for removing dissolved phosphorus (P) was evaluated in a hypolimnetic withdrawal system. Lake water collected from the hypolimnion, with phosphate (PO4-P) concentrations of 0.25 to 0.49 mg/L, was passed through a pilot-scale (pore volume, ∼0.87 m3) treatment system over two successive summers. In year 1, the hydraulic retention time (HRT) varied from 0.58 to 1.64 days and 96.1–98.1% PO4-P was removed. The HRT in year 2 was 0.31 to 0.48 days and PO4-P removal was 97.4–99.9%. Effluent pH was 11.37±0.17 and 11.96±0.17 in years 1 and 2, respectively, with the increase attributed to dissolution of CaO and Ca(OH)2 from the BOFS. The effluent was neutralized by addition of CO2(g) before the water was discharged. Vanadium and aluminum were released from the BOFS, and were subsequently removed through addition of a filter containing 5 wt.% granular zero valent iron with a balance of silica sand and by neutralizing pH. Solid phase analyses conducted on the spent media, including FESEM-EDX, XPS, FTIR, and XANES spectroscopy, confirmed the presence of calcium carbonate and calcium phosphate minerals. Diminished hydraulic performance was observed in year 1, which was attributed to CaCO3 accumulation on the spent BOFS media. Restricting ingress of atmospheric CO2 into the system in year 2 minimized the extent of CaCO3 accumulation on the treatment media and led to improved hydraulic characteristics. Results show potential for long-term removal of phosphorus.