Central composite design optimization of pilot plant fluidized-bed heterogeneous Fenton process for degradation of an azo dye

Optimization of Acid Yellow 36 (AY36) degradation by heterogeneous Fenton process in a recirculated fluidized-bed reactor was studied using central composite design (CCD). Natural pyrite was applied as the catalyst characterized by X-ray diffraction and scanning electron microscopy. The CCD model was developed for the estimation of degradation efficiency as a function of independent operational parameters including hydrogen peroxide concentration (0.5–2.5 mmol/L), initial AY36 concentration (5–25 mg/L), pH (3–9) and catalyst dosage (0.4–1.2 mg/L). The obtained data from the model are in good agreement with the experimental data (R2 = 0.964). Moreover, this model is applicable not only to determine the optimized experimental conditions for maximum AY36 degradation, but also to find individual and interactive effects of the mentioned parameters. Finally, gas chromatography–mass spectroscopy (GC–MS) was utilized for the identification of some degradation intermediates and a plausible degradation pathway was proposed.