Phosphorous Removal From Agricultural Discharge Using Calcined Lime-Based Wastes.

Phosphorous loaded on the soil by using phosphorous fertilizer can impact on water quality.   Many studies have reported that shell which contains calcium (as a form of CaCO₃, calcite) can absorb phosphorous to the shell surface.  The calcination of the shell transforms calcite as quicklime (CaO, calcium oxide) and the calcined shells can be used good sorbing agents.  The objective of this study was to evaluate the effectiveness of shell waste for the phosphorous sorbing agents. Three calcined shells, CESP (Calcined Egg Shell Powder), CMSP (Calcined Mussel Shell Powder), and COSP (Calcined Oyster Shell Powder), were selected for the model sorbents.  CaO was for the control.  For sorption equilibrium, 0.1 g shell powders were mixed with 10 mL potassium dihydrogen phosphate solution (C_i = 10, 20, 50, 75, and 100 mg P L^-1, 5 mM CaCl₂ solution) for 24 hr at a room temperature (25±5 ^oC).  After equilibrium, pH and C_eq (dissolved phosphorous concentrations) was measured.  C_s (adsorbed phosphorous concentrations) was calculated by difference between C_i and C_eq.  The effectiveness of three calcined shells for phosphorous removal was higher than that of CaO.  Especially, COSP exhibited the best efficiency for phosphorous removal.  The sorption data were found to follow the Langmuir sorption isotherm model (r² > 0.95).  At low C_eq, phosphorous sorption to shell powder was stronger.  However, above of certain concentration, the amount of phosphorous sorbed to shell powder became reduced.  In this study, the pH of equilibrium solution was very basic (pH 12.85).  At this pH range, phosphorous sorption can be greatly affected by the presence of calcium, which is a major component of calcined shells used in this study.  The experiment of calcined shell for phosphorous removal at the different pH range is on the way.