Assessment of Field Applicability of Waste Egg Shell for Removing Phosphorus from Agricultural Discharge.

 Phosphorous is known as the primary limiting factor for eutrophication. Agricultural discharge contains phosphorus loaded on the soil through the agricultural activity and transfers phosphorus to water bodies. Materials containing calcite (CaCO₃) can absorb phosphorus to the surface. Recycling the waste egg shell, which is consisted of mainly CaCO₃, is beneficial economically as well as environmentally. The objectives of this study were following: i) to evaluate the characteristics of the waste egg shell for removing phosphorus through the batch experiment. ii) to assess the field applicability of the waste egg shell for removing phosphorus through the column experiment. We conducted the batch experiment for the removal efficiency on the effect of reaction time, solid/solution ratio, and sorbent particle size. After about 48 hr, phosphorus concentration of the solution reached the plateau. When the sorbent dosage was more than 20 mg L^-1 (solid/solution ratio was 1:50), the phosphorus removal efficiency was more than 90 %. When the particle size of sorbent was < 0.5 mm, the phosphorus removal rate was about 57%. In the other particle size, the phosphorus removal rates were 85% ~ 95%. Based on these results, we conducted sorption experiment. For the sorption experiment, 0.5 g sorbent (< 1 mm) was mixed with 25 mL phosphorus solution (initial phosphorus concentration (C_i) was 0.25, 0.5, 0.75, 1, 2, 4, 6, and 8 mg L^-1 in 10 mM KCl solution) at a room temperature for 48 hr. Initial pH was adjusted 3, 5, 7, and 9 with 0.1 M HCl and 0.1 M NaOH solution. The Temkin sorption isotherm model was the best fitted to the sorption experiment data. We assessed the field applicability of the waste egg shell for removing phosphorus from the agricultural discharge through the moment analysis of the breakthrough curve (BTC) for the column test.