Recycling wasted scallop shell as an adsorbent for the removal of phosphate

Lots of scallop shells were discharged from local restaurants and marine product manufacturers around the city of Gangneung and most of them are dumped into landfill. The scallop shell was recycled as an adsorbent for the removal of phosphate. The shell size greatly affected phosphate removal. One gram of shell having diameter of around 45 μm removed 100 mg/L of phosphate in 3 h while that of 3 mm hardly removed in 80 h. Phosphate removal was not much affected by the pH in the range of 2.0–7.5 but it was scarcely removed beyond pH 8.0. Higher temperature was preferred for phosphate removal but the removal efficiency was almost constant over 35 °C. The maximum phosphate removal capacity was obtained through Langmuir isotherm plotting and it was as high as 23.0 mg-phosphate/g-shell. On the purpose of enhancing the adsorption capacity of scallop shell, it was treated with chemical reagents such as HCl, NaOH, NH₄HCO₃ and EDTA. HCl-treatment increased the adsorption capacity of the shell having diameter of 45 μm by 39.8% than raw scallop shell, but the treatment showed negligible effect on the shell of 1000 μm in diameter. Packed-bed containing HCl-treated scallop shell with 500 μm in diameter removed 20 mg/L of phosphate stably for 15 days and the removal efficiency was over 85% throughout operation.