Optimization of a textile dye degradation in a recirculating fluidized-bed reactor using magnetite/S₂O₈²⁻ process

Optimization of Acid Orange 7 (AO7) treatment using heterogeneous Fenton-like method in a recirculating fluidized-bed reactor (FBR) was investigated by using central composite design (CCD). Natural magnetite (NM) as Fenton-like catalyst was characterized using scanning electron microscopy. A nonlinear CCD model was obtained for the prediction of dye degradation as a function of experimental variables such as peroxydisulfate concentration (0.1–0.5 mmol/L), initial AO7 concentration (5–25 mg/L), pH (3–9) and NM dosage (0.25–1.25 g/L) after 105 min of treatment. The calculated results by the model were consistent with the experimental results (R² = 0.959). Furthermore, the model is suitable to estimate the optimum operational conditions and determine the effects of the parameters for maximum AO7 degradation. Eventually, gas chromatography–mass spectroscopy was used for the recognition of the dye degradation by-products.