Degradation of 1,4-dioxane by the ferrioxalate-mediated photo-Fenton process using UV or white LED irradiation

The treatment of 1,4-dioxane in wastewater is presently an issue in Japan because the pollutant is non-biodegradable and has a high solubility in water. The Fenton process, carried out in darkness, was effective in treating 1,4-dioxane in low concentrations. However, the process cannot be applied in cases of high 1,4-dioxane concentrations because the Fenton reaction is completed within 15 min. Therefore, the photo-Fenton process was evaluated for treating 1,4-dioxane present in high concentrations. The ferrioxalate-mediated photo-Fenton process, which utilizes the reduction of Fe(III) ions through ligand-metal charge transfer, uses UVA- or white-LED-irradiation to reduce energy consumption. Fe(III) ions can be reduced to Fe(II) ions even under white LED irradiation, indicating that the Fenton reaction can occur continuously. In this case 1,4-dioxane at a concentration of 100 mg/L could be degraded to less than 0.5 mg/L, which is the discharge limit for wastewater. The amount of 1,4-dioxane degraded is linearly dependent on the amount of Fe(III) reduced. The use of white LED irradiation could reduce energy consumption by 40% compared with UVA irradiation. Considering that ambient room light can also be used for degradation, the utilization of white LED light for the degradation process has promise for achieving a further reduction in energy consumption.