Enhanced dichloroacetonitrile degradation via VUV/PS: radical contributions, matrix interference, and energy considerations

Abstract Dichloroacetonitrile (DCAN), a nitrogenous disinfection byproduct, is the most frequently detected haloacetonitrile species in drinking water. This study evaluates the degradation of DCAN using vacuum ultraviolet (VUV)-based advanced oxidation processes (AOPs), compared with VUV alone. VUV-based AOPs were combined with common oxidizing agents—H 2 O 2 , Cl 2 , and persulfate (PS)—to generate reactive radical species such as HO • , Cl • , and SO 4 •– for enhancing DCAN removal. The effects of oxidant dosage, humic acid, and inorganic constituents in water were systematically examined. Results showed that first-order rate constants for DCAN degradation using VUV/PS (20–100 mg PS L –1 ) were higher than those observed with VUV/Cl 2 (2 mg Cl 2 L –1 ), VUV, and VUV/H 2 O 2 . Increasing PS doses enhanced DCAN removal rates, while increasing Cl 2 and H 2 O 2 doses (10–100 mg L –1 ) either reduced or had minimal effect on degradation efficiency. The highest removal rate constant (0.37 min –1 ) and efficiency (100% in 6 min) were achieved with VUV/PS at 100 mg PS L –1 in phosphate buffered. The predominant degradation mechanism in VUV, VUV/Cl 2 , and VUV/PS systems was indirect photolysis via HO • radicals, contributing 58, 53, and 88%, respectively. Hydroxyl radicals played the dominant role in DCAN degradation due to higher second-order rate constant of DCAN with HO • (3.3 × 10 9 M –1 s –1 ) compared to SO 4 •– (6.4 × 10 8 M –1 s –1 ). Among the water matrix constituents tested, bicarbonate significantly inhibited DCAN degradation. The VUV/PS system (100 mg PS L –1 ) demonstrated the lowest energy consumption (4.0 kWh m –3 ) and cost (USD 0.41 m –3 ). These findings provide valuable insights mechanism and for selecting optimal oxidants of VUV-based AOPs for efficient DCAN removal.