(225g) Heterogeneous Fenton Oxidation of Synthetic Dye in Water With Surface-Modified Iron-Amended Activated Carbon

The present study aims to develop effective adsorption and oxidation of synthetic dye in wastewater by using newly synthesized nano iron catalyst-deposited activated carbon. Recently synthetic dye-containing wastewater has gained more attention due to its mass discharge, high toxicity and low biodegradation. For enhancing adsorption of dye and oxidative regeneration of dye-exhausted activated carbon, the novel synthesis of nano iron-deposited granular activated carbon (GAC) was developed. It was to amend ferrous iron onto the acid-pretreated GAC followed by Fe amendment onto the acid-pretreated GAC when pH of iron solution was higher than the pH at point of zero charge (pH, _pzc) of the GAC. Methylene blue (MB) in water was adsorbed onto the iron-amended GAC (Fe-GAC) followed by single or multiple applications of H₂O₂. Batch experiments were carried out to study the adsorption isotherm and kinetics at at 20°C and pH 6 with the initial concentration of 20-200 mg/L and the solution pH of 6.0. It showed that the adsorption isotherm for MB onto Fe-GAC followed Langmuir isotherm, yielding maximum monolayer adsorption capacity (q_m) of 238.1 ± 0.78 mg/g which is higher than the virgin GAC with q_m of 175.4 ± 13.6 mg/g at 20°C and pH 6. The kinetics of adsorption results indicated that pseudo-second order kinetics represented adsorption of MB. The heterogeneous Fenton oxidation of MB in the Fe-GAC showed increasing the H₂O₂ concentration from 7 to 140 mmol H₂O₂/mmol MB led to enhancing  the oxidation efficiency of MB in the GAC from 62.6% to 100%, respectively. The half-life of the H₂O₂ showed the range between 1.4 to 39.4 h depending on the H₂O₂ concentrations at a fixed iron loading of 6 mg Fe/g GAC. The oxidation of MB in the GAC increased at the higher initial concentration of H₂O₂ and Fe²⁺ because of the increased generation of hydroxyl radicals. Further enhancement of oxidation of MB in the Fe-GAC was made by the multiple injection of H₂O₂ whileminimizing OH radical scavenging often occurring at high concentration of H₂O₂. The re-adsorptive capacity of the Fe-GAC showed 87-92% over the repeated multiple cycle of adsorption and oxidation of MB indicating effective treatment of MB in wastewater. Further works will include development of diffusion-reaction model and the optimization of the operating conditions over the repeated cycles of adsorption and oxidation.