Efficient simultaneous degradation and dechlorination of Chlorophenylacetonitrile by vacuum ultraviolet-sulfite advanced reduction system

Disinfection by-products (DBPs) in chlor(am)inated drinking water and wastewater pose risks to human health and ecological safety. Studies on the degradation of the formed DBPs, especially aromatic DBPs, are quite limited. Recently, advanced reduction processes (ARPs), generating highly reactive reductive radicals to break the carbon-halogen bonds, as an emerging technology for refractory organic compound degradation has attracted attention. This study, for the first time, explored the degradation of a representative nitrogenous and aromatic DBP, 2-chlorophenylacetonitrile (2-CPAN), by VUV/UV/sulfite-based ARP system, and investigated the underlying mechanisms and influencing factors. The results demonstrated that VUV/UV/sulfite process achieved over 98.6% and 86.8% degradation of 2-CPAN from tap water and wastewater within 60 minutes although inorganic ions existing in real waters slightly inhibited its degradation, highlighting its potential for practical application in real waters. Due to VUV direct photolysis and the generation of more reactive species, VUV/UV/sulfite exhibited superior performance in 2-CPAN degradation (98%) than UV/sulfite (81%). Furthermore, VUV/UV/sulfite process maintained a stable degradation efficiency across a wide range of pH (5-11) and sulfite dosages (0.25-5.0 mM), and achieved 90% degradation even under oxic conditions. Mechanism studies confirmed the presence of hydrated electrons (e⁻_aq), hydroxyl radicals, and hydrogen radicals in VUV/UV/sulfite system, with e⁻_aq identified as the primary contributor to 2-CPAN degradation. Chlorine in 2-CPAN was primarily released as chloride ions, achieving 94% dehalogenation within 15 minutes. The above findings revealed that VUV/UV/sulfite could be a promising technology for aromatic DBP degradation in real waters.