Degradation of Toluene from Gas Streams by Heterogeneous Fenton Oxidation in a Slurry Bubble Reactor with Activated Carbon-Based Catalysts.

A novel approach for the treatment of volatile organic compounds from gaseous streams was developed. In order to accomplish this, a semi-batch bubble reactor was used, aiming to assess the toluene (selected as model compound) degradation from gaseous streams via heterogeneous Fenton oxidation. Activated carbon-based catalysts-metal-free or iron-impregnated-with different textural and chemical surface properties were used for the first time as catalysts, in order to degrade gaseous toluene using such technology. Complementary characterization techniques, such as nitrogen adsorption at -196 °C, elemental analysis, pH at the point of zero charge (pHPZC), inductively coupled plasma optical emission spectrometry (ICP-OES) and transmission electron microscopy (TEM), were used. The materials' chemical surface properties, particularly the presence of N-surface groups, were herein found to play an important role in toluene adsorption and catalytic performance. The maximum amount of toluene transferred, 6.39 × 10-3 mol, was achieved using melamine-doped activated carbon (N-doped material) that was impregnated with iron (sample herein called ACM-Fe). This iron-based catalyst was found to be quite stable during three reutilization cycles.

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, Qair = 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.

Insights into real industrial wastewater treatment by Fenton's oxidation in gas bubbling reactors.

In the present study, bubbling reactors (BRs) were chosen to design a new procedure for real industrial wastewater (WW) treatment by Fenton's oxidation. The process was carried out in BRs under batch mode for the treatment of a WW with a high organic load (chemical oxygen demand (COD) above 7000 mgO2/L), being the efficient mixing of the liquid phase ensured by the gas bubbling. The parameters that influenced the WW treatment (i.e., H2O2 and Fe2+ concentration, and initial pH) were optimized in a smaller BR (0.5 L volumetric capacity); the maximum oxidation efficiency (dissolved organic carbon (DOC) removal = 52% and COD removal = 83% after 60 min) was reached under the following conditions: Qair = 1.0 L/min (measured at room temperature and atmospheric pressure), [H2O2] = 22.5 g/L, [Fe2+] = 0.75 g/L, and pH = 4.6 - original WW pH. It was not detected any significant effect in the process efficiency of the air flow rate and gas phase composition (i.e., N2, and air), but when the process was performed with continuous O2 bubbling an increase in the DOC removal (from 43% to 53%) was observed after 5 min of oxidation. Even so, the high costs discourage the use of pure oxygen streams in real WWTPs. To understand the dynamics of the process, the continuous air bubbling was compared to another mixing mode (mechanical stirring), and similar mineralization was achieved, proving the feasibility of Fenton's process in a BR. In addition, the gas bubbling proved to be more efficient in terms of heat dissipation during the treatment, decreasing temperature profiles along the oxidation of heavily charged real effluents. An effective scale-up with a bubble column reactor with a higher volumetric capacity by a factor of almost one order of magnitude was also proved, providing similar mineralization. The final effluent was non-toxic and more biodegradable.