Degradation of 3-methylindole by ionizing radiation: Performance and pathway

Nitrogenous heterocyclic compounds (such as 3-methylindole) are common refractory organic pollutants in coal chemical wastewater, which cannot be effectively removed by conventional wastewater treatment processes. Therefore, advanced treatment process is required to eliminate them. In this study, ionizing radiation technology was used to degrade 3-methylindole. The influencing factors, including absorbed doses (1, 2, 3 and 5 kGy), initial concentration of 3-methylindole (5, 10, 20 and 50 mg/L), and pH (3, 5, 7 and 9) on the degradation of 3-methylindole were investigated. The results showed that the removal efficiency of 3-methylindole was 96.2% when initial concentration was 20 mg/L, absorbed dose was 3 kGy, and pH was 3. The quenching experiments indicated that hydroxyl radicals, hydrated electrons and hydrogen radicals contributed to 3-methylindole degradation. The intermediate products during the process of 3-methylindole degradation were identified by LC-MS analysis, including anthranilic acid (2-aminobenzoic acid), gentisic acid (2-hydroxybenzoic acid) and 1,2,4-trihydroxybenzene (benzene-1,2,4-triol). The possible degradation pathway was proposed based on the identified products. The toxicity of 3-methylindole and its intermediates were predicted by using ECOSAR, suggesting that the intermediate products of 3-methylindole degradation had lower toxicity than 3-methylindole. This study provided an insight into 3-methylindole degradation by ionizing radiation.