Degradation of chloroaniline in chemical wastewater by ionizing radiation technology: Degradation mechanism and toxicity evaluation

Chloroaniline is a typical organic pollutant in chemical wastewater, which cannot be effectively removed in conventional wastewater treatment processes. In this study, ionizing radiation was used as advanced treatment process to degrade 2-chloroaniline (2-CA). The results showed that 10 mg/l of 2-CA could be completely degraded at 1 kGy. The required dose for completely degrading 2-CA by radiation increased when its initial concentration increased. Solution pH affected 2-CA degradation by changing the radiation-chemical yield of reactive species. Chloride ions (10 and 100 mM) had not obvious influence on 2-CA degradation. Hydrogen radicals, hydrated electrons and hydroxyl radicals, all contributed to the degradation of 2-CA, but with different degradation mechanisms. Hydrogen radicals and hydrated electrons could initiate reductive dechlorination of 2 CA, while hydroxyl radicals can degrade 2-CA by hydroxylation. 6-amino-1,4-cyclohexadiene and chlorobenzene were the main intermediate products of 2-CA degradation in the hydrogen radicals or hydrated electrons dominant process; while o-hydroxyaniline and nitroso-chlorobenzene were the main intermediate products in the hydroxyl radicals dominant process. The solution toxicity after radiation treatment varied with the initial concentration of 2-CA and the absorbed dose. In the actual chemical wastewater, 2-CA can be effectively removed by radiation, even in the presence of high concentration of chloride ions (about 2800 mg/l). The solution toxicity of actual wastewater decreased with the increase of adsorbed dose. This study provided an insight into the 2-CA degradation by radiation, and demonstrated that radiation could be an alternative option for the treatment of chloroaniline-containing chemical wastewater.

Automated summary

This study found that ionizing radiation can effectively degrade chloroaniline in chemical wastewater, even in the presence of high chloride ion concentrations. The solution toxicity of actual wastewater decreased with the increase of absorbed dose.