• UV/H2O2 achieved 90% degradation of kathon (CMI-MI) within 20 min at 0.3 mmol·L–1 H2O2, with 35% mineralization after 40 min.
• The process is robust across pH 4–10 and unaffected by common anions (SO4^2-, Cl-, NO3-, NH4+), except carbonate which inhibits removal.
• UV/H2O2 is more energy-efficient and cost-effective than UV/PS, as indicated by lower EEO values.
• Post-treatment biodegradability is significantly enhanced, supporting integration with biological processes for eco-friendly wastewater treatment.