Removal of azo dye acid red 88 by Fenton based processes optimized by response surface methodology Box-Behnken design

The acid red 88 (AR88) is a dye used by manufacturing sector like leather, cosmetic, textile, rubber, pharmaceutical, paper industry, printing etc. When disposed without proper treatment in water streams, dyes are not easily degradable since they are stable to light and resistant to oxidizing agents. Advanced oxidation processes (AOPs) have been recognized as successful and feasible technologies for recalcitrant and/or toxic contaminant removal. These processes are based in the production of hydroxyl radicals (HO^•) which are non-selective and highly reactive with an oxidation potential of 2.80 V.

The aim of this work was to create a statistical model using a Response Surface Methodology – Box-Behnken design, to better predict and understand the influence of different operational conditions. Three variables were studied: H₂O₂ concentration (0 – 8 mM), Fe²⁺ concentration (0 – 0.30 mM) and UV-A radiation intensity (0 – 32.7 W m^-2). For the best operational conditions obtained by the RSM model (pH = 3.0, [H₂O₂] = 7.9 mM, [Fe²⁺] = 0.22 mM, time = 30 min), different radiation sources were applied (UV-C, UV-A, ultrasound (US) and solar), with US and solar achieving the highest kinetic rates (k_US = 0.083 and k_solar = 0.179 min^-1) regarding UV-C and UV-A (k_UV-C = 0.064 and k_UV-A = 0.071 min^-1). In addition, it was observed that solar reactor had the lowest operational cost, regarding energy consumption. Based in the results it can be concluded that application of RSM models is a useful tool that allows to improve the optimization of AOPs in textile dye degradation.