**3. Results and Discussion**

## *3.1. E*ff*ect of Eggshell Dosage*

Different amounts of eggshell (0.25, 0.5, 1.0, 1.5, and 2.0 g) were added into DB78 solutions to analyze the effect of adsorbent dosage on adsorption. The effect was investigated at an initial concentration of 25 mg/L, pH 5, 120 min of contact time, constant stir (500 rpm), and room temperature (25 ◦C). The results obtained from this study are shown in the plot of dye removal (%) versus adsorbent dosage (g), as can be seen from Figure 1.

**Figure 1.** Effect of eggshell amount on the adsorption of Direct Blue 78 (DB78).

The increase of the adsorbent led to a slight increase for dye removed until a maximum adsorption. This reveals that the removal efficiency of dye increased with increasing amounts of eggshell. At a dosage of 0.5 g, the removal of dye was similar to higher doses (1–2 g), therefore, in order to optimize the adsorption process, and so to use the minimum amount of adsorbent, 0.5 g of eggshell was used in order to study the kinetic and equilibrium experiments.
