Abstract
In this study, hydrochar-based-eggshell was prepared via the subcritical water medium (SCWM) and used as a catalyst in the thermally activated peroxide oxidation (TAPO) approach for crystal violet and dye bathing wastewater degradation. The catalytic activities for the raw eggshell (RES) and hydrochar-based-eggshell (HES) were compared. RES and HES were characterized using a scanning electron microscope (SEM),energy-dispersive X-ray spectroscopy (SEM-EDX), and Fourier transforms infrared spectroscopy (FT-IR). The affecting parameters on the degradation process were optimized using response surface methodology (RSM). The effects of temperature (293–333 K), amount of catalyst (5–25 mg/50 mL), the concentration of H2O2 (0–8 mM), and treatment time (10–70 min) on the TAPO method were investigated using central composite design (CCD). For the crystal violet removal, two models were developed. Both models were significant and can be used to describe the design space. Also, the dye bathing wastewater degradation was described by another developed model, which had a high correlation coefficient (R2 = 0.97). In general, catalytic activity for HES was higher than RES. The degradation of crystal violet reached 98.10% when a 20 mg HES catalyst and 6 mM H2O2 at 323 K for 55 min were used. While 97% of the color of dye bathing wastewater was removed in 55 min at 323 K using 25 mg of HES and 4 mM H2O2. This study showed that the hydrolyzed eggshells could be used in the oxidation of crystal violet and dye bathing wastewater by the thermally activated peroxide oxidation method.
•The catalytic efficiency of raw and hydrolysed eggshell in TAPO was evaluated.•Hydrolysed eggshell provided high removal yield in crystal violet and dye bathing wastewater.•Crystal violet and dye bathing wastewater were removed by 98.10% and 97%, respectively.•The effects of the experimental variables were evaluated and optimised using RSM.