<p>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—H₂O₂, Cl₂, and persulfate (PS)—to generate reactive radical species such as HO^•, Cl^•, and SO₄^•– 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&#xa0;mg PS L^–1) were higher than those observed with VUV/Cl₂ (2&#xa0;mg Cl₂ L^–1), VUV, and VUV/H₂O₂. Increasing PS doses enhanced DCAN removal rates, while increasing Cl₂ and H₂O₂ doses (10–100 mg L^–1) either reduced or had minimal effect on degradation efficiency. The highest removal rate constant (0.37&#xa0;min^–1) and efficiency (100% in 6&#xa0;min) were achieved with VUV/PS at 100&#xa0;mg PS L^–1 in phosphate buffered. The predominant degradation mechanism in VUV, VUV/Cl₂, 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 × 10⁹ M^–1 s^–1) compared to SO₄^•– (6.4 × 10⁸ M^–1 s^–1). Among the water matrix constituents tested, bicarbonate significantly inhibited DCAN degradation. The VUV/PS system (100&#xa0;mg PS L^–1) demonstrated the lowest energy consumption (4.0 kWh m^–3) and cost (USD 0.41&#xa0;m^–3). These findings provide valuable insights mechanism and for selecting optimal oxidants of VUV-based AOPs for efficient DCAN removal.</p>