Contribution of Reactive Species to Nitrogen Transformation during Radiolytic Degradation of Aniline

The ionizing radiation technique has been powerful to treat nitrogen-containing organic pollutants, but the nitrogen transformation mechanism, which is directly linked to remediation efficiency and system toxicity, is poorly understood. Herein we show that by 60-Co-γ rays’ irradiation, nitrogen in aqueous aniline was transformed to nitrate (NO3–), nitrite (NO2–), nitrogen-containing intermediate products, ammonium (NH4+), and gaseous nitrogen compounds. Specifically, hydrogen radicals (H·) played a major role in the formation of NO3–, while hydroxyl radicals (HO·) played an important role in the formation of nitrogen-containing degradation products. The introduction of hydrogen peroxide promoted the formation of nitrogen-containing degradation products while reducing the production of NO3–. Pulse radiolysis experiments demonstrated that the coexistence of HO· and O2 accelerated the decomposition of transient intermediate products compared to pure HO·, which boosted the aniline decomposition and the nitrogen conversion. The presence of inorganic ions had a concentration-dependent impact on the nitrogen conversion. Additionally, nitrogen-containing degradation products presented acute and chronic toxicity. While ionizing radiation can effectively remove aniline from actual wastewater, the toxicity of actual wastewater after treatment at 10 kGy increased. This study provides valuable insights into the nitrogen transformation within aniline and the associated toxicity changes during the ionizing radiation treatment process.