Removal of selected hazardous organic compounds by electro-Fenton oxidation process.

摘要

Electro-Fenton oxidation process is used to remove selected hazardous organic compounds from aqueous solutions. Hydrogen peroxide (H₂O ₂) is electro-generated by the reduction of dissolved oxygen in acidic solutions.{09}The optimal conditions are cathodic potential of −0.5V vs. saturated calomel electrode (SCE), oxygen mass flow rate of 8.2 × 10 −2 mol/min, and pH 2. The average current density and current efficiency are 6.4 A/m2 and 81%, respectively. Fe2+ is electro-regenerated from ferric salt or Fenton's iron sludge. The optimal cathodic potential is −0.1 V vs. SCE. At this potential, the average current density is in linear proportion to [Fe3+] ₀, showing a slope of 8.48 × 10−3 (A/m 2)(mg/L)−1. The average current efficiency varies with [Fe3+]₀, i.e., 75% at [Fe3+] ₀ = 100 mg/L and 96∼98% at [Fe3+]₀ ≥ 500 mg/L. Fe2+ can also be effectively regenerated from Fenton's iron sludge. The Fenton oxidation process can effectively degrade all selected polycyclic aromatic hydrocarbons (PAHs), namely, naphthalene, fluorene, phenanthrene, fluoranthene, pyrene, and anthracene. A “time-squared” kinetic model, C = C₀ exp(− k_obst2), is developed to describe the reaction kinetics in the continuous dosing mode. Methanol and ethanol inhibit the PAHs degradation by competing for hydroxyl radicals. The Fenton oxidation process is also used to degrade selected chlorinated aliphatic hydrocarbons (CAHs), namely, tetrachloroethylene (PCE), trichloroethylene (TCE), 1,1-dichloroethylene (DCE), and chloroform. PCE, TCE and DCE can be effectively degraded, while chloroform is difficult to degrade due to their structure difference. The dosing mode of H₂O₂ and Fe2+ significantly affects the reaction efficiency. Trichloroacetic and dichloroacetic acids are the major byproducts in the oxidation of PCE and TCE, respectively. Based on the byproducts identified, possible reaction pathways are established and kinetically modeled. Electro-Fenton oxidation process is more efficient than conventional Fenton oxidation process due to the continuous regeneration of Fe2+ at the cathode. This demonstrates that the electro-Fenton oxidation process is an effective technology for the removal of hazardous organic contaminants from aqueous solutions.