Industrial wastewater treatment using a bubble photo-Fenton reactor with continuous gas supply

The present study assesses the treatability of a real industrial wastewater (WW) with a high organic load (chemical oxygen demand (COD) above 5800 mgO₂ L^-1) by photo-Fenton's oxidation with the goal of improving the organic matter degradation reached previously, in another work, where the Fenton process was applied in a bubbling reactor. Thus, the process was carried out in a bubble photo reactor (BPR) wherein continuous air supply ensures an efficient mixing of the liquid phase. The effect of the main operatory parameters that influence the WW treatment (i.e., H₂O₂ and Fe²⁺ concentrations, initial pH, and UV-Vis radiation intensity) were evaluated, being found that in the best conditions tested (pH₀ = 4.6, [Fe²⁺] = 0.1 g L^-1, [H₂O₂] = 18 g L^-1, Q_air = 1.0 L min^-1-measured at room temperature and atmospheric pressure-and irradiance of 500 W m^-2), removals of 95% and 97% for total organic carbon (TOC) and COD, respectively, were achieved. Still, a high reduction of the concentration of the main constituents of this WW was reached, being total for aniline and 86% for sulfanilic acid. The continuous air supply reactor configuration was compared with magnetic stirring; similar mineralization was achieved. However, the air bubbling promotes a good heat transfer within the reactor, minimizing temperature gradients, which is quite advantageous due to the strong exothermicity of the oxidation process during the treatment of such highly loaded real effluents.