Solar light irradiation activated dichloramine for efficient abatement of micropollutants

Dichloramine (NHCl₂), typically formed during wastewater treatment processes involving chloramine and chlorine, has recently emerged as a potential oxidant for contaminants degradation. This study systematic explores the utilization of solar-activated NHCl₂ for efficient degradation of micropollutants. The results indicate that solar/NHCl₂ process effectively removed 53.5-100% of micropollutants within 10 min, with corresponding pseudo-first-order rate constants (k_obs) of 0.0519 - 0.7044 min^-1, under the conditions of pH 5.0 and 100 μM NHCl₂. In addition, the quantum yield of NHCl₂ is relatively stable, approximately 0.085 mol/Einstein, within the pH range of 3.0-7.0. HO^• and Cl^• were identified as the primary reactive species for the degradation of ibuprofen (IBF) and carbamazepine (CBZ) in this process through kinetic modeling and quenching experiments. The contribution of HO^• to IBF and CBZ reached 55.27% and 58.02% respectively, followed by Cl^• with contribution rates of 35.97% and 39.99% respectively at the conditions of 100 μM NHCl₂ and pH 5.0. Additionally, the degradation efficiencies of IBF and CBZ gradually increased with the concentration of NHCl₂ increasing from 25 μM to 100 μM. Modeling and experimental results show that Cl^- and SO₄^2- had hardly effect on the degradation of IBF and CBZ. HCO₃^- inhibits the degradation of IBF and CBZ by scavenging HO^• and Cl^•. Humic acid (HA) inhibits not only by scavenging HO^• and Cl^• but also by light filtering. Furthermore, the degradation pathways of IBF and CBZ were investigated, with primary degradation mechanisms including hydroxylation, chlorination, and bond cleavage. Then, the formation of seven chlorinated disinfection byproducts (DBPs) from IBF and CBZ was investigated. In summary, this study demonstrates the potential of the solar/NHCl₂ process.